Has natural selection really been tested and verified?
Yes, in fact it has been tested and verified so many times that it has been validated to a very high degree.
There are so many observations and studies of natural selection causing a shift in the frequency of genetic traits from one generation to the next, that it is difficult not to find cases where it occurs.
I am not so sure that this is true. Can people point to tests that have verified that natural selection causes evolutionary change? What tests have they conducted? Do these tests accurately mimic the real world?
First you need to define what you mean by "evolutionary change" - so we can see if your meaning is similar to what is used in the science of biology in general and evolution in particular.
In science "evolutionary change" means that the frequency distribution of hereditary traits is different from one generation to the next. I expect you are thinking of something more dramatic than variations on a theme changes.
Second, you need to distinguish between the observable phenomenon of natural selection as a process of life, and the theory of Natural Selection as part of an explanation for the diversity of life as we know it.
I would like to stipulate that talking about bacteria (in any form) does not qualify as any type of test, because ultimately we must be taking sexual reproduction, where choices are being made into account-so bacteria is out.
Curiously, natural selection involves survival and reproduction, such that those individuals which are more successful at surviving and reproducing will pass on more genes to the next generation than those that are less successful. It doesn't matter if reproduction is sexual or asexual.
Ok, so what are these tests which prove (or even provide solid evidence for) ...
In science - all science - nothing is proven. The best we have are highly validated theories with mountains of evidence supporting the theory and no contradictory or anomalous evidence. The best we can say is that this means that the theory is a good approximation of the truth.
Gravity fits this level of validation. Natural selection fits this level of validation.
Thus the solid evidence available provides a sound basis for concluding that the theory is a good approximation of the truth.
... provide solid evidence for) natural selection is the driver of evolutionary change?
Natural selection is only part of the process of evolution, the change in hereditary traits in populations from generation to generation - other major contributors are mutation and genetic drift. Mutation provides new variations to the mix of hereditary traits that are then susceptible to the action of natural selection, and genetic drift is where stochastic effects (natural disasters etc) change the population that is then left for evolution by mutation and natural selection.
So, what you mean by "evolutionary change"? What do you expect to see?
Enjoy.
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The supposition made by the magazine editor (not by me)was that Darwin's idea of natural selection has been tested to be the driving force of evolutionary change (including of course changes in body structures, and living systems, etc).
Now we have a little more description of what you are meaning by "evolutionary change" and I have to note that changes in "body structure and living systems" are actually the accumulation of many smaller changes, taking place over multiple generations, so no, you are not going to see this kind of change in one study. This is similar to asking to see mountains rise and erode in the course of one or two years.
What the author of the article in Discover meant is not shown here - we have no quotes from the article itself, and unfortunatey you did not provide a link, the title of the article, or even the date when your article was published. This makes it difficult to reply to what "supposition made by the magazine editor" involves.
Going to the Discover Magazine website and doing a search for "Natural Selection Darwin" gives me this link:
and this one:
But the content of these articles is nothing like what you are saying: can you provide a citation for the article in question?
Note further, that Discover Magazine is a "popular science" magazine, the articles are written by journalists not scientists, the articles are edited for popular appeal, and it not a peer reviewed journal, so it is not a reliable source for actual science. It can be a fun read, and if you are truly interested in a topic covered by the magazine, then you should follow the references
So far it seems the "tests" you and others have mentioned as evidence, provide nothing in the way of showing that it was " Darwin's natural selection" that caused this evolutionary changes._In fact what they all demonstrate is that a change was "needed" in a population and the change occurred.
Curiously, these are sufficient within the science of biological evolution, as the science is understood and used by the scientists. If you disagree, then you have a problem with learning the proper terminology to discuss this.
Evolution in general, and natural selection in particular, does not manufacture what is "needed" -- this is false thinking, and nobody in any of the biological sciences suggest this, nor did Darwin.
Evolution is a response mechanisms: the ecology changes, and
if the change is sever enough the species will go extinct,
if some small percentage of the population survives due to having certain traits in the surviving individuals that the majority did not have, then the traits, and only the traits, of the surviving individuals will be passed on to the next generation,
if the change is moderate such that most individuals survive, then there will be more of a mixture of surviving traits to be passed on to the next generation
What the process of survival and reproduction accomplishes is surviving and breeding individuals that are better at surviving and breeding than other individuals within a breeding population, and thus the hereditary traits they have become shared to a greater extent within the population.
Natural selection operates on the existing traits within the existing population to select the traits that are best suited to the ecology around the individuals.
That is quite a different thing from showing that random mutations slowly drifted through the populations along with every other kind of random mutation, causing the change.
Mutations don't "drift through the populations" - you are not understanding the process that is involved.
To see what evolutionary biologists say, rather than populist journalists and editors.
This was a random mutation that just so happened to crop up exactly in a population that was experiencing the disease, in exactly the right time(down to the decade) t
You are misreading this article. The beneficial mutation existed before the epidemic occurred:
quote:Scientists from the MRC Prion Unit, a national centre of excellence in prion diseases, assessed over 3000 people from the affected and surrounding Eastern Highland populations, including 709 who had participated in cannibalistic mortuary feasts, 152 of whom subsequently died of kuru. They discovered a novel and unique variation in the prion protein gene called G127V in people from the Purosa valley region where kuru was most rife.
Those who participated in the cannibalistic mortuary feasts and did not die, 709 - 152 = 557 people, already had the mutation, or they would have died as well:
This gene mutation, which is found nowhere else in the world, seems to offer high or even complete protection against the development of kuru and has become frequent in this area through natural selection over recent history, in direct response to the epidemic. This is thought be perhaps the strongest example yet of recent natural selection in humans.
The frequency of the hereditary trait increased in the population as a whole because the survivors had the mutation and then passed it on to their descendants while those that perished did not. Notice that a human generation is ~20 years on average, and you need to get from an initial mutation - which is neutral when there is no disease present - to a population of 557 descendants.
I wonder who that 'one" individual is who happened to be around at just the right time to father the entire population of children and pass on the resistance is?
Except (a) it wasn't "at the right time" but well before the epidemic or only the one person would have survived, rather than the evidence of it already being extant in a large number of people (do you have 557 children?) and (b) you didn't read the notes that show only women and young children engaged in the mortuary feast, not men, so the mutation in a man during the epidemic would have had no effect on survival of people.
The other studies mentioned, such as Galapagos finches and Peppered moths, these are all old stories about evolution, but in what way do they test or show the randomness of the mutations and that caused these shifts in populations?
Congratulations, this is a poor debate tactic called "moving the goalposts" -- you originally asked for examples of tests of natural selection: the examples given do that to a "T" as they demonstrate differential survival and the resultant shift in the frequency of hereditary traits in following generations -- and now you are complaining that they are not tests of random mutations.
And also, since in cases like the Galapagos finches, the populations oscillate back to their original forms of shorter beaks, under different environmental conditions, we have to show the same processes happening twice-first a random mutation causes longer beaks to sprout and then those get chosen within the population, and then later wouldn't you know it, another "random" mutation comes along and the exact same slow weeding out process of mates choosing the best beak sizes happens again; and fortuitously the need for a certain beak size remains the single most important consideration for mate selection over the vast spaces of time that natural selection requires. Quite amazing.
Interestingly your opinion, misrepresentation and incredulity are unable affect reality.
(1) the mutation did not occur AFTER the change in ecology, there was existing variation in the population, with a large percentage having large beaks and a small percentage with small beaks. The ones with big beaks can eat the available food easier than the ones with small beaks, with the result that they are healthier and have more time for reproduction.
(2) when the ecology changed the existing individuals with small beaks were favored and the ones with large beaks had trouble surviving: the population shifted to having a large percentage having small beaks and a small percentage with large beaks. The ones with small beaks can eat the available food easier than the ones with big beaks, with the result that they are healthier and have more time for reproduction.
(3) when the ecology returns to what it was in (1) above then once again the existing individuals with big beaks were favored and the ones with small beaks had trouble surviving: the population shifted to having a large percentage having big beaks and a small percentage with small beaks. The ones with big beaks can eat the available food easier than the ones with small beaks, with the result that they are healthier and have more time for reproduction.
No new mutations needed at all.
Similar for the Peppered Moths: both varieties live at the same time, but one is heavily selected against in one ecology, then the other is heavily selected against when the ecology changes, and then this shifts back when the ecology shifts back and the former variety is once again heavily selected against.
This is what I meant by evolution being a response mechanism: some individuals have a better opportunity to survive and reproduce than others, with the response result that they are better represented in the next generation,
but the opportunities change with the changes to the ecology around them (or when they move into new ecologies), with the response result that other individuals are better represented in the next generation, ones that have a better opportunity to survive and reproduce than others.
Or even more amazing still, we have a entire list of traits we are selecting for over many many years of generations, overlapping each other- lung capacity, tail size, genital size, coloration, chirping sound, eyesight, nest building techniques, proper digestive gland sizes, and on and on..and each and every one of these needs is remaining constant long enough after all these random mutations occurred to eventually trickle their way through the selection process. So each time a beak size is being chosen for, all of these other criteria, and about 100,000 = others are also being selected for. It must be a tough choice for a pretty female finch to decide.
I'm sorry, but your impression of how evolution works is extensively incorrect and misinformed. Please read the links provided above - they are used by universities teaching Master's and PhD programs in biological evolution to students learning to become biologist and evolutionist scientists. The information on these two websites is accurate, specific and much more reliable than what you have learned.
You have 2 populations of finches. One has small beaks the other has large beaks.
No, you have one population of breeding individuals with variation in the size of the beaks, from small to large.
During the wet times there are more small beak finches. During the dry times there are more large beak finches.
During climatic changes to the ecological environment that span several years (ie not just seasonal changes involved) the frequency distribution of beak sizes changes in the population, with small beaks being favored in the wetter ecology and large beaks being favored in the dryer ecology.
It only has to do with who has the most food. The one that does produces more offspring with a better survival rate. Thus you have more of one than the other.
Which is how natural selection works as a part of evolution.
That has nothing to do with evolution.
Incorrect, it is fundamental to evolution. Without selection there would be no diversity of life.
They not evolving anywhere. They are simply oscillating back and forth with the one with the most food having more offspring.
Correct, evolution does not have a direction, and thus oscillation back and forth is just as much evolution as any gradual trend in one direction (larger beaks over time) or the other (smaller beaks over time).
Evolution is a response mechanism, and thus when climatic changes oscillate back and forth over long time periods, then selection will take place such that the population oscillates to match the changes in the ecology (or perish).
So what does this test prove.
That natural selection does occur in the field, and it can be documented as the response to specific ecological changes. In wet ecologies selection occurs in one direction, in dry ecologies selection occurs in the other direction.
These are just short term changes, the changes in the frequency of hereditary traits within a breeding population that occur from generation to generation based on (a) the ecology where the species lives, and (2) the available variations within the species population.
For longer term changes you need to consider that evolution is a 2-step dance, an endless do-loop program:
Mutations occur randomly during pre-reproduction in the reproductive cells of an organism, during the reproductive process when DNA is copied with some changes due to copy errors, and during the organism development process as the organism is growing by cell division. The ones that don't result in death of the individual before reproduction can get passed on to the next generation. This includes beneficial mutations, neutral mutations, and mildly deleterious mutations. By the time an individual organism reaches reproductive age the mutation process has stopped for that individual: they are either fit to survive and breed in their ecology or they are not.
Selection occurs on the existing variations and acts on the individuals within a breeding population. Those that survive long enough to breed then passing their hereditary traits on to their descendants in the next generation of the breeding population. Those that are better able to breed more often (healthier, well fed, longer lived, attractive to mates, etc) will produce more offspring, and thus their hereditary traits will have a higher frequency distribution in the next generation then those less able to breed often.
Evolution occurs on the breeding population as a whole, not on the individuals, through population dynamics. As the frequency distribution of hereditary traits within a population changes so too do the breeding opportunities change, with the result that more successful traits spread through the population and less successful traits become less common.
They are simply oscillating back and forth with the one with the most food having more offspring.
Meanwhile, selection neutral hereditary changes in the population - changes that do not affect relative survival in wet/dry selection - can still occur in the population such that there is a difference between the initial wet ecology population and the repeated wet ecology population, changes that either occurred due to secondary selection for the dry ecology, or changes that are of a different trait unrelated to wet or dry ecologies.
Example: tail length could be selected for longer tails by sexual selection, and this process would continue through the dry period and the return to the wet period, but the population in the second wet period would all have longer tails than the population in the first wet period.
If you wish to win an argument based on sheer volume of typing, I will simply defer now.
When you ask a question or make a comment that needs a long explanation to cover all the points you have raised, then you can expect a long response. Typically such questions and comments are due to being wrong or misinformed about certain aspects of the topic, so those erroneous bits need to be corrected: the more erroneous bits in your questions and comments, the longer a full response will be. The alternative is just to say that you are ignorant of the topic, which I agree is no answer.
I won't however defer based on your tired and worn out theme of "well you just don't know biology, so you are wrong" argument (I even suggested when I first proposed this topic that this type of defense be excluded, because its simply not saying a dam thing.., but the admin required me to remove that part of my suggestion-although I knew it wouldn't take long for someone to drag it out).
Which is why I provided sources for you to look at and determine for yourself if you are right or wrong. This is also why I explained at length why your information was false.
Either don't complain about the length or don't complain about being labeled as uninformed.
For the record, these are comments of yours that are either wrong or confused (taken from one paragraph in Message 17):
what they all demonstrate is that a change was "needed" in a population and the change occurred.
random mutations slowly drifted through the populations along with every other kind of random mutation,
and these are comments of yours that are either wrong or confused (taken from another paragraph in Message 17):
funny that one would cite a population of people developing a resistance to disease in a few decades as evidence that Darwin's theorized process of slow gradual change,
a random mutation that just so happened to crop up exactly in a population that was experiencing the disease, in exactly the right time(down to the decade)
That is some serious good fortune.
I wonder who that 'one" individual is who happened to be around at just the right time
to father the entire population of children and pass on the resistance
I guess the entire population can be traced by to one very prolific and possibly still alive reproducer.
That is one very inbred society
The entire population was fathered by one man (or woman), who might even still be alive!
That's 10 erroneous comments in two paragraphs of a relatively short post. The astute reader will note that the second list is just about every comment you made in that paragraph.
I know exactly what the theory suggests, every bit as much as you do.
Obviously not, as you would not make such a plethora of false and confused statements if you did understand the theory of natural selection and the process of evolution, as it is used in biological sciences by biological scientists and as documented in the links I provided.
What you have is an opinion based on erroneous information, either through misunderstanding of the science, or through your being given false information instead of actual information about evolution.
I think you answers are basically fit for a 7 year old. I appreciate your participation, but honestly I wasn't coming here to get a 6th grade lecture from you-I come here seeking depth and insight.
Amusingly, this means that you should be able to understand it then, yes? You should also be able to comprehend when you are wrong, and have the cognitive skills to update your thinking with proper information (ie - go to links to university programs on evolution: you should be able to understand them as well, yes?).
First, I could provide the exact article for this quote, but it is beside the point.
Please do - it is very much the point, as you are using it to claim that some authority made the comment, and that authority has not been established. Please also provide the link where you found the article if that is different from the actual article.
Message 24: The author of the study himself declared that this resistance happened in a matter of a few decades.
Please quote where he says that. Here is the link again:
quote:Lead author Professor John Collinge, Director of the MRC Prion Unit said:
It’s absolutely fascinating to see Darwinian principles at work here. This community of people has developed their own biologically unique response to a truly terrible epidemic. The fact that this genetic evolution has happened in a matter of decades is remarkable. Kuru comes from the same disease family as CJD so the discovery of this powerful resistance factor opens up new areas for research taking us closer to understanding, treating and hopefully preventing a range of prion diseases.
The study A Novel Protective Prion Protein Variant that Colocalizes with Kuru Exposure, which began in 1996, will be published in the New England Journal of Medicine on 19 November 2009.
Where does it state when the mutation occurred? The selection occurs over a period of decades, because the selection is a simple pass\fail survival test, but we don't know when the mutation occurred.
The fact that there were 577 descendants of the "father" (or mother) with the original mutation speaks to it having occurred many many generations before the epidemic. If we assume three offspring per generation reach the age of reproduction to pass on the mutation, and an average generation time of 20 years, this works out to 116 years minimum (assuming the gene was always passed on to children, and that no intermarriage of descendants occurred even though 6 generations is enough to allow intermarriage in most cultures, especially with tribal customs). If we assume that the mutation was only passed to half of the children this grows to 314 years and 16 generations minimumbefore the epidemic. The actual time is likely even longer.
Note that we do not know when Kuru first developed.
Kuru (disease) - Wikipedia
[quote]Kuru was first noted in the Fore tribe of the Eastern Highlands Province of Papua New Guinea as Australian administrators explored the area in 1957—1959. It was in the late 1950s that the full extent of the disease was realized, after it had reached large infection rates in the South Fore of the Okapa Subdistrict, though the agent was unknown.[6][/qs]
So it could have existed before then, and people with the mutation could have been descendants of survivors of previous exposure to the disease.
quote:changes in "body structure and living systems" are actually the accumulation of many smaller changes, taking place over multiple generations, so no, you are not going to see this kind of change in one study.
I think this provides your answer with much more brevity. No this can't be tested.
Nor is this natural selection, rather it is the whole process of evolution - the change in the distribution of hereditary traits in breeding populations from generation to generation - taken over many generations and involving many different hereditary traits being combined.
Furthermore, I take exception with your claim that by asking for evidence of natural selection creating evolutionary change, it is moving the goal posts to require that this takes random mutations into account.
You asked if natural selection was really tested and verified (see topic title), not whether macroevolution - the long term result of evolutionary change in diverging species over many generations - had been tested and verified.
If you don't feel that random mutations must be evidenced in the study of natural selction-then what the heck are we saying exactly?
That mutation\variation and natural selection are two different processes within evolution. A rather simple concept.
That some animals with bad gentics die, and some with good gentics live longer? Ok, I accept that. So what does that tell us about anything?
That natural selection occurs, and that it has been tested and verified.
You mean to suggest that you wanted to just take the literal meaning of natural, and the literal meaning of selection and show that things are natural, and thing are selected?
Curiously, that is exactly what Darwin meant when he formulated the theory of Natural Selection
Another good link to actual information about evolution in general and Darwin's theory in particular, eh?
If people in one region of the world suddenly develop a resistance to a rare disease, a resistance people in other parts of the world never seem to spontaneously develop, we must think long and hard about how and why that happened. Was it really just that one guy happened to get this fortunate mutation. Do people in other parts of the world occassional get a similar random mutation? Do people in other parts of the world occassionally get born with resistance to bubonic plague, to Lou Gehrig's disease, to the anthrax virus, to arsenic? How often does this happen randomly?
Often enough, and sufficiently prior to selection pressure (NOT suddenly) for the surviving species to survive, OR they are not endemic enough to wipe out a surviving species (other populations protected by being geologically separated), OR the species go extinct.
Fascinatingly, extinction is a frequent occurrence in the natural history of life on earth.
If you wish to argue the finer points of evolution, you can't just gloss over all the logical assumptions one must make to have the theory make any sense at all.
We have now established that natural selection is an observed, tested and verified process within evolution. No assumptions required for that.
Next, if you wish, we can discuss whether mutations are an observed, tested and verified process within evolution. Do you want to start a thread on that (so that the two processes can be discussed separately) or do you want to continue on this thread, now that your original question - Has natural selection really been tested and verified? - has been answered, and accepted as true?
How can there be one population if there are 14 different species?
You are confusing the number of different species on the different Galapagos Islands, with the observed changes within one species on one island.
Each species is a breeding population defined (originally by geographic isolation) that is reproductively isolated by behavior or infertility. Some of the species occasionally interbreed and produce hybrids, but this is rare, and the different ecologies on the different islands tend to maintain the overall differences.
... now the finer points? Nope, back to quibbling, while being still dead wrong
Hi Bolder-dash, still having trouble I see,
For the record, these are comments of yours that are either wrong or confused (taken from one paragraph in Message 17):
1. "what they all demonstrate is that a change was "needed" in a population and the change occurred" 2. random mutations slowly drifted through the populations along with every other kind of random mutation,
and these are comments of yours that are either wrong or confused (taken from another paragraph in Message 17):
You are going to need to improve your comprehension skills, before you can so arrogantly accuse others of not understanding.
Point: I NEVER said that the Theory suggests changes based on need, I said that the evidence from those studies only demonstrate change when it was needed! I was saying the exact opposite of what you inferred. Here is the exact quote:
"So far it seems the "tests" you and others have mentioned as evidence, provide nothing in the way of showing that it was " Darwin's natural selection" that caused this evolutionary changes._In fact "what they all demonstrate is that a change was "needed" in a population and the change occurred." (color added for emphasis)
Funny how I read your words to say "what they all demonstrate is that a change was "needed" in a population and the change occurred" (your exact words according to you when you repeated them) and concluded that you said:
1. "what they all demonstrate is that a change was "needed" in a population and the change occurred"
Amusingly, you will now please note that what I quoted was your words verbatim and thus that you are accusing yourself of saying the exact opposite of what you said.
Point: I NEVER said that the Theory suggests changes based on need, I said that the evidence from those studies only demonstrate change when it was needed!
Daylight is needed for life to exist, but that doesn't mean that it occurs in response to that need, or that need is even relevant to the question of evolution.
The point remains that your comment: "what they all demonstrate is that a change was "needed" in a population and the change occurred" (which you will again note is quoting you verbatim) is still wrong, dead wrong, because the same "need" existed for the people who died as for those that lived, however the mutation did not save them, it did not, in fact, occur in their lineage, and it did not in fact occur in time to save them.
I say "the tests you provided don't indicate random mutations and then slow eventual change but rather demonstate changes occurring quickly when needed", ...
And you are still wrong, dead wrong, in regard to those people who died. Need has nothing to do with whether or not mutations occur: mutations are random events.
"So far it seems the "tests" you and others have mentioned as evidence, provide nothing in the way of showing that it was " Darwin's natural selection" that caused this evolutionary changes.
Correct, because now you are talking about evolution and not just natural selection -- you have moved the goalposts from just natural selection to the whole process of evolution. Don't complain that the tests don't show evolution when you asked for tests showing natural selection, when evolution is more than just natural selection.
What you are doing, as has been pointed out several times now by several different people, is confusing natural selection with the whole process of evolution. Natural selection is responsible for selecting the best mix of hereditary traits in a population to fit the ecology they live in, mutations provide random variations, that once are available to the population become susceptible to natural selection. It is a two step process in an endless do-loop:
(1) mutations provide variation within a breeding population,
(2) natural selection acts on existing variations in a population,
... go to step (1)
When you talk about changes in species over time:
Message 17: ... Darwin's idea of natural selection has been tested to be the driving force of evolutionary change (including of course changes in body structures, and living systems, etc).
So far it seems the "tests" you and others have mentioned as evidence, provide nothing in the way of showing that it was " Darwin's natural selection" that caused this evolutionary changes.
You are now talking about evolutionary change and significantly more than the process of just natural selection, you are talking about taking several steps down the evolutionary path. To walk down a path from an existing species to one with "changes in body structures, and living systems" requires that those changes become available to selection during the walk, and thus this necessarily introduces the rest of the evolutionary process -- mutations, genetic drift, population dynamics, behavior, etc etc etc.
Natural selection acts to select the hereditary traits that are better fit to an existing ecology, by the differential reproductive and survival ability of individuals carrying different mixes of existing mutations. If a trait does not exist at the time of selection the individual or the population suffers, as the people that died from kuru died, because for them the mutation did not exist.
From this one example, you should now be able to recognize what a beneficial mutation is: a mutation that arises in a population, and then, when tested by natural selection, proves to provide a benefit in survival or reproduction for the individuals that inherit the mutation compared to the rest of the population.
ie - this mutation is now identified as a beneficial mutation.
It does not matter when the mutation arose, or what the selection test actually was, only that some individuals were carriers and others were not, and that this difference resulted in increased survival and reproduction for the carriers compared to the non-carriers.
Now, I noticed that you did not reply about the other 8 misunderstandings of yours, nor have you provided the article link that you said you could, to the Discover article. My personal opinion is that when you do provide the link (if ever) we will find that it does not begin to show what you have claimed.
I am curious to know how natural selection or genetic drift create EVOLUTIONARY CHANGE? Please elaborate. I challenge you to do so without talking about mutations. Seeing as how natural selection and genetic drift create no new information at all, and on their own say absolutely nothing other than some organisms die before they can reproduce.
Has natural selection really been tested and verified?
Yes, in fact it has been tested and verified so many times that it has been validated to a very high degree.
There are so many observations and studies of natural selection causing a shift in the frequency of genetic traits from one generation to the next, that it is difficult not to find cases where it occurs.
I am not so sure that this is true. Can people point to tests that have verified that natural selection causes evolutionary change? What tests have they conducted? Do these tests accurately mimic the real world?
First you need to define what you mean by "evolutionary change" - so we can see if your meaning is similar to what is used in the science of biology in general and evolution in particular.
In science "evolutionary change" means that the frequency distribution of hereditary traits is different from one generation to the next. I expect you are thinking of something more dramatic than variations on a theme changes.
Second, you need to distinguish between the observable phenomenon of natural selection as a process of life, and the theory of Natural Selection as part of an explanation for the diversity of life as we know it.
I would like to stipulate that talking about bacteria (in any form) does not qualify as any type of test, because ultimately we must be taking sexual reproduction, where choices are being made into account-so bacteria is out.
Curiously, natural selection involves survival and reproduction, such that those individuals which are more successful at surviving and reproducing will pass on more genes to the next generation than those that are less successful. It doesn't matter if reproduction is sexual or asexual.
The change in the frequency distribution of hereditary traits in breeding populations from one generation to the next is evolution, and in these cases it has been caused by natural selection.
In these cases it has been tested.
In these cases it has been verified.
There are many more cases, so many in fact that it is ludicrous to argue the point that natural selection is an observed fact of biological life as we know it.
Seeing as how natural selection and genetic drift create no new information at all, and on their own say absolutely nothing other than some organisms die before they can reproduce.
The point that you are ignoring is that selection results in some surviving and reproducing better than others, and that this alone can result in diversity.
Take two sub-populations of the same species, each living in a different ecology: the traits that lead to improved survival and reproduction in one are necessarily different from the other (by definition of ecology), and thus the selection pressure will be different, and the traits selected in descendant populations will be different in the two different ecologies. Over time the variations in each subpopulation will have different frequency distributions of hereditary traits. They will evolve on different paths. They will necessarily diverge over time.
Evolution - the process - is the change in the frequency distribution of hereditary traits in breeding populations from generation to generation.
This is observed to have occurred in these instances, and thus evolution, by the process of natural selection in response to ecological change, has been observed.
Could you please give me the definition of species again ...
There are many definitions of species, and what is critical to evolutionary science is not what a specific definition involves, but whether the process of speciation is observed.
Speciation is the process where a parent population is divided into reproductively isolated sub-populations, where the daughter populations no longer exchange genetic\hereditary information by interbreeding and become distinct breeding populations now subject to independent evolution within their respective populations. This is what results in the formation of trees of relationships and common ancestry relationships.
No longer joined at the ancestral hip they are free to diverge each within their own ecologies.
Arbitrary speciation can also be recognized when the amount of hereditary change in a lineage adds up to the same degree of difference from an ancestral population that occurs with reproductive isolation, and this is commonly used to assign new species names, although this is subject to subjective interpretation (hence "arbitrary"). This does not lead to the formation of trees of relationships and common ancestry relationships, so it is relatively unimportant to the broad scheme of things.
Hi Bolder-dash, still having that comprehension problem eh?
First, let's say organisms never mutated, and reproduced exactly the same way each time-could natural selection work then?
Yes. The case examples given in Message 5 don't involve mutations during the selection period, and amazingly natural selection still occurred.
Or what if Lamark was right, then natural selection could certainly not apply.
Curiously, this was one of the ways Darwin actually considered new traits to arise, and then be subject to selection. The ability of acquired traits to be inherited has since been falsified, but that doesn't change the fact that selection operates on the phenotype - the acquired development of an organism - and thus acquired traits that are non-hereditary can contribute to selection. They just generally are not passed on to the following generation and thus do not contribute to long term change in the frequency distribution of hereditary traits in breeding populations from generation to generation. Note that behavior can cause acquired traits, so that if behavior is passed from generation to generation it can have an effect. See "memes" for more on this concept.
Message 91 The real problem isn't me bringing mutations into the discussion, anyone who is intellectually honest knows that that is a vital ingredient of natural selection-without it natural selection does not exist, because change in the organism doesn't exist.
Still incorrect. New traits do not occur, but natural selection still occurs, only longer trend evolutionary change involving new traits does not. This difference is the difference between natural selection as part of evolution and evolution as an entire process.
Natural selection is a vital ingredient to evolution, and mutation is also a vital ingredient to evolution, and without both of these ingredients long term evolution of different species would not occur.
If you want to discuss the arrival of new traits in species over time then necessarily you need to discuss a mechanism for new traits to arise. We now know that new traits arise by mutations. This too is an observed fact.
Message 22: Ok, fair enough, I am willing to modify my statement to include what is the modern day accepted form of Darwinian evolution..that is that random mutations are the ingredients for change, and natural selection the filter. If you are in the camp of suggesting that this is not a viable theory, or you believe the modern theory of evolution differs from this, feel free to say so. I hope you can agree to either accept this theory (with caveats of genetic drift, and others if you so choose) or reject it to keep the discussion on topic.
Taking this as an admission that your OP was flawed in presentation, we can indeed move forward. The basic problem remains that evolution encompasses more than just these simple processes when the overall picture is viewed.
However, be that as it may, we have now recognized two processes in the overall evolution of species:
Natural selection - the process that selects among the existing phenotypes of a species those that are best able to survive and breed, by the simple expedient of their survival and breeding within the ecology in question. This results in a descendant population with (a) a different frequency of hereditary traits from the parent population, and (b) a population that is better fit to survive and breed in the ecology in question.
Mutation - adds random variation to the mixture of hereditary traits available in a breeding population, by the simple expedient of causing changes to the genetic make-up of individuals. Whether these new variations are beneficial, deleterious or neutral is unknown until selection has an opportunity to operate on the variation/s.
If the individual organism with a new mutation dies before reproduction, the mutation is considered deleterious, and it has been selected AGAINST being passed to the next generation, and it does not result in any change to the frequency of hereditary traits available in the breeding population.
If the individual organism with a new mutation survives and breeds better than other organisms, the mutation is considered beneficial, and it has been selected FOR being passed to the next generation, and it does result in change to the frequency of hereditary traits available in the breeding population.
If neither occur then the mutation is neutral, and can still spread within the population, and it does result in change to the frequency of hereditary traits available in the breeding population.
To derive change that is more than just an oscillation between different existing traits under different ecological conditions, new traits need to be introduced, resulting in different results than just oscillations. These different results can be unrelated to the selection for ecological change, such as ones due to sexual selection for desired mating traits that are independent of survival traits.
By this process long term change in species occurs, a gradual change that is beyond the capability of mere oscillation between previous hereditary traits to develop.
The dashed lines show the overall trend. The species at the bottom is Pelycodus ralstoni, but at the top we find two species, Notharctus nunienus and Notharctus venticolus. The two species later became even more distinct, and the descendants of nunienus are now labeled as genus Smilodectes instead of genus Notharctus.
As you look from bottom to top, you will see that each group has some overlap with what came before. There are no major breaks or sudden jumps. And the form of the creatures was changing steadily.
Notice that the size distribution in P.jarrovii is completely outside the size distribution in P.ralstoni and that when speciation occurs that a divide in the size distribution quickly develops, showing that the populations are reproductively isolated.
In each population along these time-lines natural selection operates to keep the breeding population centered around the size best suited for survival in the ecology, including the ability to find mates and survive within the population.
The overall increase in size is due to new mutations that allow larger body size to develop. The speciation event occurs originally as a distribution with two high peaks, peaks that become more separated as additional mutations allow both larger and smaller individuals to exist and be part of the selection spectrum.
The result is speciation, diversity, additional features that were not in the original population, evolution.
This is but one of many examples of speciation, where natural selection is the driving force for adaptation of species to different ecological niches, the filter that weeds out deleterious mutations and disadvantageous phenotypes from the mix of individuals that form the parents of the following generation/s.
To recap:
Natural selection is an observed process, a fact of biology.
Mutation caused variation is an observed process, a fact of biology.
Other processes also contribute to the overall evolution of species, including neutral drift, individual development, behavioral patterns and changing ecologies.
Speciation is an observed process, involving mutation and natural selection, and is also a biological fact.
Evolution - the change in frequency distribution of hereditary traits in breeding populations from generation to generation - is also an observed biological fact.
The theory of evolution - ToE - can be stated simply as the hypothesis that the process of evolution - the change in frequency distribution of hereditary traits in breeding populations from generation to generation - is sufficient to explain the diversity of life as we know it, from the world around us, from history, from pre-history, from paleontology and archaeology, from the fossil record and from the genetic record.
This includes natural selection as the filter, and mutations as the source of new material for the filter to act on.
As such, I have proposed a new topic, which discusses the meaning of natural selection and what is the definition of the ToE.
Now I note that you are attempting to start another thread without first dealing with the definition of evolution (which includes, but is not limited to, natural selection). My response is at Definition of EvolutionMessage 212
I thought evolution was a process that eventually wound up in a different place. Not something that just kept going back and forth from one state ot another.
Then you have learned that you were wrong in this assumption. Evolution has no direction, it is just a response mechanism not a developmental mechanism.
As you have just said, The change in the frequency distribution of hereditary traits in breeding populations from one generation to the next is caused by random mutations, then natural selection.
So if the change in frequencies from one generation to the next is caused by random mutations, how can we talk about evolution occurring without showing that it was random mutations? You are trying to have your cake and eat it too.
The change in frequency distribution of hereditary traits in breeding populations from generation to generation can be caused by: (1) random mutations (2) natural selection (3) stochastic events (4) neutral drift (5) etc (6) any combination of the above
Certainly natural selection only operates on the existing phenotypes of the individual organisms within the breeding population, while mutations have a time-lag before their effect is likely felt within the breeding population and then the selection process.
You can think of natural selection as operating on ancestral mutations - ones in the parent or older population - that exist in different frequencies in the current population, and that affect the population dynamics of breeding the next generation.
Without the concept of random mutatins causing evolutionary change, we don't have evolution-and yet you don't want to discuss random mutations.
Not quite. Random mutation is a part of the evolutionary process, as is natural selection. Random mutation is not a part of natural selection and natural selection is not a part of random mutation.
Only when we discuss the process of evolution can we discuss both mutation and natural selection as contributing factors.
And I can certainly understand why you don't want to discuss random mutations, because having it make sense scientifically is pretty hard to do.
Actually it is rather simple.
Say you want to throw all 6's with 10 dice. You can throw for a long time before getting this result, but if after every throw you take the ones that are 6's and set them aside, you will reach all 6's in considerably shorter time.
The throws are random results, selection picks the 6's at each generation of throws. If you only have one throw, the probability of getting all 6's is extremely low for either approach. Thus the additional generations of throws represent the effect of random mutations on the previous non-6's population to also adapt and become 6's in the final population. (please note that this is an analogy and does NOT mean that the same mutations arise in subsequent generations, rather that "6" represents a fitness level within the ecology, as several different mutations can result in fitness in different ways).
To recap-
1.Evolution is RANDOM MUTATIONS and NATURAL SELECTION
Among other processes, yes, and these are the major sources of new traits and the selection of new traits in the overall scheme of life.
2. To show scientifically that evolution has occurred, we have to prove that it was BOTH things acting together. So if either one happens without the other, its not evolution correct?
Not quite, as noted back at the beginning, the change in the frequency distribution of hereditary traits in breeding populations from generation to generation can occur through just natural selection, and it can occur through just mutations because the frequency does change as a result.
However, the long trend in evolution is for both to occur in a multi-step pattern:
During breeding the effects of mutation are seen in the new generation being produced, plus the effect of selection of old mutations on the current breeding population.
Then natural selection operates on the individual phenotypes, the developed organisms, that are a product of their genetics and the developmental environment, including learned behaviors.
The ones that survive and breed then contribute to the next generation and
go to (1) ...
One follows the other, even though both are occuring simultaneously, their effects are felt at different times in the lives of the individual organisms.
So now you want to prove scientifically that any tests show evolution occurred, but when asked to prove that it was TRULY RANDOM MUTATIONS occurring, all of you keep complaining that you shouldn't have to prove that it was RANDOM MUTATIONS happening!
And yet, curiously, we have evidence of each happening, both in the lab and in the field, AND we have evidence of the overall pattern of evolution, involving both mutation and natural selection, resulting in speciation events, where reproductively isolated populations are developed, by mutation and natural selection, from a parent population.
So will you now concede that in order to discuss evolution, we need to discuss both?
I will concede precisely what I said in my first response to you (Message 5):
quote:Hi Bolder-dash, and welcome to the fray.
Has natural selection really been tested and verified?
Yes, in fact it has been tested and verified so many times that it has been validated to a very high degree.
There are so many observations and studies of natural selection causing a shift in the frequency of genetic traits from one generation to the next, that it is difficult not to find cases where it occurs.
I am not so sure that this is true. Can people point to tests that have verified that natural selection causes evolutionary change? What tests have they conducted? Do these tests accurately mimic the real world?
First you need to define what you mean by "evolutionary change" - so we can see if your meaning is similar to what is used in the science of biology in general and evolution in particular.
In science "evolutionary change" means that the frequency distribution of hereditary traits is different from one generation to the next. I expect you are thinking of something more dramatic than variations on a theme changes.
Second, you need to distinguish between the observable phenomenon of natural selection as a process of life, and the theory of Natural Selection as part of an explanation for the diversity of life as we know it.
I would like to stipulate that talking about bacteria (in any form) does not qualify as any type of test, because ultimately we must be taking sexual reproduction, where choices are being made into account-so bacteria is out.
Curiously, natural selection involves survival and reproduction, such that those individuals which are more successful at surviving and reproducing will pass on more genes to the next generation than those that are less successful. It doesn't matter if reproduction is sexual or asexual.
Ok, so what are these tests which prove (or even provide solid evidence for) ...
In science - all science - nothing is proven. The best we have are highly validated theories with mountains of evidence supporting the theory and no contradictory or anomalous evidence. The best we can say is that this means that the theory is a good approximation of the truth.
Gravity fits this level of validation. Natural selection fits this level of validation.
Thus the solid evidence available provides a sound basis for concluding that the theory is a good approximation of the truth.
... provide solid evidence for) natural selection is the driver of evolutionary change?
Natural selection is only part of the process of evolution, the change in hereditary traits in populations from generation to generation - other major contributors are mutation and genetic drift. Mutation provides new variations to the mix of hereditary traits that are then susceptible to the action of natural selection, and genetic drift is where stochastic effects (natural disasters etc) change the population that is then left for evolution by mutation and natural selection.
So, what you mean by "evolutionary change"? What do you expect to see?
Enjoy.
(color for emphasis)
You will note that from the start the issue of mutations was discussed as a necessary part of long term evolution. In other words you have forced me to concede that my original position was correct.
Or are you still equivocating on this point? In other words, its only evolution if it has both.
Except that this is still wrong.
Evolution involves a number of processes, including natural selection and mutation, and any one or any combination that results in the change in frequency of hereditary traits in breeding populations from generation to generation is evolution, by definition.
Again, I also will point you to Definition of Evolution, Message 212, for a more complete definition of evolution and the theory of evolution, where this last point is made in more detail.
Revised topic: Has speciation been tested and verified.
Hi Bolder-dash,
are you tired of whining yet? Tired of playing misunderstood? Done with playing the victim?
Your side has very little in the way of hard scientific evidence which can show that natural selection has been the cause of the diversity of life on earth.
Little has been presented, because your initial posts were so confused, we thought you were talking about only tests of natural selection.
Silly us, we didn't read your mind.
If you ever figure out what you really want examples of, then let us know.
Now, if you want to talk about how diversity occurs via evolution, for example, that is an entirely different concept, and one not limited to natural selection.
What you want to talk about is speciation: speciation is where diversity begins, as during speciation events a parent population divides into two daughter populations that become reproductively isolated, stop sharing genetic material, and then evolve along different paths due to different ecologies and selection pressure. The daughter populations become increasingly diverse from each other after the speciation event, for the simple reason that there is no process to make them to be similar.
Natural selection is one of the processes that causes this, mutations are also a necessary part of speciation, but these are not the only mechanisms involved.
quote:Speciation is the evolutionary process by which new biological species arise. The biologist Orator F. Cook seems to have been the first to coin the term 'speciation' for the splitting of lineages or 'cladogenesis,' as opposed to 'anagenesis' or 'phyletic evolution' occurring within lineages.[1][2] Whether genetic drift is a minor or major contributor to speciation is the subject of much ongoing discussion. There are four geographic modes of speciation in nature, based on the extent to which speciating populations are geographically isolated from one another: allopatric, peripatric, parapatric, and sympatric. Speciation may also be induced artificially, through animal husbandry or laboratory experiments. Observed examples of each kind of speciation are provided throughout.[3]
Please note that last part: observed examples of each kind of speciation are provide. In other words, speciation has been tested and verified (as has natural selection, as has mutations, as has genetic drift, as have all the other mechanisms of evolution that go into the overall process).
As noted on Definition of EvolutionMessage 212, a definition of evolution is provided that I have referred you to several times, but you seem to have ignored. Here is is in full:
Since there have been a number of posters claiming that 'natural selection" has no specific meaning other than one stronger organism surviving while another weaker one perishes (in any means under any circumstances, a bomb, genocide, whatever), I think this now calls into question exactly what the definition of the ToE says.
Can we please have a complete definition of what is the Theory of Evolution?
I suggest we first define what is meant by evolution as a biological process, and then discuss what is meant by the theory of evolution.
As a biological process, evolution is a change in the frequency distribution of hereditary traits in breeding populations from generation to generation. This change occurs as a result of a number of other contributory biological processes, including
natural selection, by survival of individual organisms with hereditary traits that improve their relative ability to survive,
natural selection, by reproduction of individual organisms with hereditary traits that improve their relative ability to reproduce,
mutations, that cause random changes to hereditary traits, some beneficial, some deleterious, and some neutral when viewed in context of selection of organisms that have the new mutations,
neutral drift, or neutral selection, where the variations that are neutral to selection pressures change over time, thus altering the total make-up of hereditary traits within the breeding populations but not resulting from selection,
stochastic processes, random disasters wiping out sectors of a breeding population, and in the process altering the total make-up of hereditary traits within the breeding populations but not resulting from selection,
developmental processes, changes in the development of organisms from conception to reproductive ability that are due to environmental factors,
population dynamics, the limited ability of large populations to share new hereditary traits through normal reproduction over time,
population dynamics, the limited ability of large populations when they are divided into sub-populations, especially when these sub-populations are living in different ecologies with different selection pressures,
behavior patterns that can affect survival and breeding that are passed from generation to generation by learning (memes),
isolation mechanisms, mechanisms that tend to isolate sub-populations from breeding, either geographical, temporal or behavioral,
reproductive isolation, resulting in daughter populations that no longer share new hereditary traits, and thus are free to diverge into new, albeit related, species,
common ancestry, results from speciation events, where daughter populations continue to diverge by the processes of evolution in independent ways due to different ecological pressures, and results in the formation of a tree of life, or cladistic relationships, depending on the time scale of observation,
etc
It needs to be noted that each one of these contributory biological processes has been observed and validated to occur in nature as well as in the lab: these biological processes are facts, not theory. Each of these processes can contribute in different degrees to the evolution of a species at different times, and there is no set mixture of these processes for the overall process of evolution to occur, as long as the end result is a change in the frequency distribution of hereditary traits in breeding populations from generation to generation. Thus too, the biological process of evolution has been observed, and is a known fact. Speciation has been observed as well, and is a known fact of biological evolution - the science of studying evolutionary processes in biological systems.
It also needs to be noted that there are random factors introducing changes to the distribution of hereditary traits, and there are response factors, where the result is a response to external ecological constraints on the populations.
Darwin's insight was that natural processes could accomplish the same kind of selection as was observed in the artificial selection of animal breeding programs (dogs, cows, etc), and that this selection process could account for the diversity of life as we know it, from the world around us, from history, from the natural history of the planet, and the fossil record. Since Darwin's time some of his original concepts (such as how variation was acquired), have been discarded in favor of new information not available then (such as genetics), but the overall concept that all of the diversity of life could be explained by the process of evolution has remained.
This is the root of the theory, the facts of the known biological processes form the foundation, and the overall process of evolution is hypothesized to apply to all changes in the past: The theory of evolution (ToE), simply stated, is that the diversity of life as we know it today -- from history, from prehistory, from paleontology, from the natural history of the planet, from the fossil record, and finally from the genetic record of life -- can all be explained by the biological process of evolution, a change in the frequency distribution of hereditary traits in breeding populations from generation to generation.
Evolution - the process - is an observed process and is a fact, including but not limited to speciation events that cause division of breeding populations into distinct sub-populations that can evolve independently.
Evolution - the science - is the study of the biological processes that lead to evolution in breeding populations and to speciation and the development of long term trends in diversity due to common ancestry, and the formation of various cladistic branches and their inter-relationships as a result of continued evolution after speciation.
Evolution - the theory - is the hypothesis that the process of evolution - change in the frequency distribution of hereditary traits in breeding populations from generation to generation - is sufficient to explain the diversity of life as we know it.
It should also be noted, that framed this way, the Theory of Evolution is a very robust theory, not just because it has been validated by thousands of concurring observations and an absolute absence of contradictory evidence (not one change has been observed that is not due to a known biological process), but because falsification of one part of the processes contributory to the overall process does not invalidate the overall theory. The theory, however is falsifiable -- just demonstrate that a specific observed change cannot possibly be caused by these biological processes.
Note that there are 12 processes listed, two involving natural selection (one for survival and one for reproduction), and one for random mutations, and that the list is incomplete.
Evolution is the change in the frequency distribution of heritable traits in breeding populations from generation to generation. It does not matter which individual process or what combination of these processes is involved in any specific instance, as long as the change occurs, it IS evolution.
Evolution is constantly ongoing, and there is no known species where evolution is not occurring.
I gave you the example of Pelycodus (Message 126) as a record of speciation in the fossil record, and showed how both natural selection and mutation assisted that process, as indeed they are normally present in most speciation events. The simple fact is that during the speciation process daughter populations are being selected for different ecologies, and over time the differences in mutations available (new and old), and in the selection pressures from the different ecologies, necessarily result in different end species.
This is the source of diversity. Without speciation all life would be one species.
Please note that I consider someone who first complains that my first reply did not answer the question (Message 17), and then later claims (Message 132) that I am being forced to concede that my first reply was correct, to be someone who is not debating in good faith. Either they are extremely confused about what they are actually talking about, or they are playing some kind of game.
Now the question is: are you going to improve your behavior?
Enjoy.
Edited by RAZD, : some content hidden per moderator request
I do not feel that the ToE is an adequate explaination as to the origins of life ...
You are likely to get a bunch of replies to this comment. The ToE does not attempt to explain the origins of life, that is a separate science called abiogenesis.
quote:In the natural sciences, abiogenesis, or "chemical evolution", is the study of how life on Earth could have arisen from inanimate matter. It should not be confused with evolution, which is the study of how groups of living things change over time. Amino acids, often called "the building blocks of life", can form via natural chemical reactions unrelated to life, as demonstrated in the Miller—Urey experiment and similar experiments, which involved simulating the conditions of the early Earth. In all living things, these amino acids are organized into proteins, and the construction of these proteins is mediated by nucleic acids. Which of these organic molecules first arose and how they formed the first life is the focus of abiogenesis.
This is a fairly new science, and there are a lot of unknowns involved in it. Suffice to say that at this point we don't know how or when life began, we just know that after some point at least 3.5 billion years ago that there is evidence of life. From that point to the present it appears that evolution is sufficient to explain the diversity of life.
... or the existance of life as we know it. I have no problem with "facts of evolution" (when they are indeed facts), what I have a problem with is when "theories of evolution" and "evolutionary history" is presented as fact.
Theories are called theories because they are not facts, rather they are explanations of facts, with the best theories offering the best explanations. Theories can be validated but never proven, and are at best held as tentative approximations of reality until a better theory comes along.
Theories are also falsifiable, which does not apply to facts, and the Theory of Evolution is falsifiable.
Put briefly, the theory of evolution is that the process of evolution - the change in the frequency distribution of hereditary traits in breeding populations from generation to generation - is sufficient to explain the diversity of life as we know it. This can be falsified by demonstrating some part of the diversity of life that is not and cannot be explained by evolutionary processes. The complete sudden appearance of an entirely new type of life, for example.
Where my problem lies is what the limits are that NS can accomplish.
What limits natural selection is two things: the ecology in question, and the hereditary traits available in the breeding population. NS doesn't create new features, it selects among the existing features in the breeding population of adult phenotypes the ones that are best adapted to survive and breed within the ecology.
My thinking was that once a species was reprodutively isolated NS could no longer come into play, since reproduction was no longer possible. A few posts that I have read since then, I realize that may be too simplistic. I still have some questions about that topic though. (maybe speciation should be a seperate thread, but since I am talking about it in context of NS ...)
Indeed it could be a separate thread, however speciation is the point at which diversity in life begins, and this is part of Bolder-dash's revised topic (as far as I can determine), so I think a brief discussion is okay.
Once populations become reproductively isolated, then evolution continues to occur, just within each breeding population rather than the (parent) super-population. Thus one daughter population will evolve through evolution (mutation, natural selection, etc) to adapt to its ecology, and the other daughter population will evolve (in a different way) through evolution (mutation, natural selection, etc) to adapt to its ecology, in much the same way that two different species will evolve differently.
I thought that would make them technically part of the same species. Can reproductive isolation and therfore speciation, be established on pre-mating barriers only? I thought there needed to be genetic incompatability. Could the Galapogos finches still be considered of the same "genetic" species?
Again, the critical element is whether the populations are reproductively isolated. This isolation can occur pre-mating based on changes to mating behavior. In the Asian Greenish Warbler we see this behavioral isolation in effect:
quote:Greenish warblers (Phylloscopus trochiloides) inhabit forests across much of northern and central Asia. In central Siberia, two distinct forms of greenish warbler coexist without interbreeding, and therefore these forms can be considered distinct species. The two forms are connected by a long chain of populations encircling the Tibetan Plateau to the south, and traits change gradually through this ring of populations. There is no place where there is an obvious species boundary along the southern side of the ring. Hence the two distinct 'species' in Siberia are apparently connected by gene flow. By studying geographic variation in the ring of populations, we can study how speciation has occurred. This unusual situation has been termed a 'circular overlap' or 'ring species'. There are very few known examples of ring species.
Note that there is technically gene flow around the plateau, but in practical terms it takes generations for genes from one end to possibly reach the other end, and the probability of such flow is low, due to the reduced mating in the hybrid zones.
Do I understand this correctly: that these hybrdization 'zones' allow enough genes to be shared that it prevents the individual species from becoming genetically incompatable?
Sometimes yes, sometimes no. It depends on the viability of the hybrids in question to act as go-betweens with fertile and fecund reproduction.
Note too, that there are generally considered to be four forms of speciation events:
quote:Speciation is the evolutionary process by which new biological species arise. The biologist Orator F. Cook seems to have been the first to coin the term 'speciation' for the splitting of lineages or 'cladogenesis,' as opposed to 'anagenesis' or 'phyletic evolution' occurring within lineages.[1][2] Whether genetic drift is a minor or major contributor to speciation is the subject of much ongoing discussion. There are four geographic modes of speciation in nature, based on the extent to which speciating populations are geographically isolated from one another: allopatric, peripatric, parapatric, and sympatric. Speciation may also be induced artificially, through animal husbandry or laboratory experiments. Observed examples of each kind of speciation are provided throughout.[3]
For instance if you compared the DNA from Geospiza fortis to that of Geospiza magnirostris, could the traits that makes the two species genetically incompatable (if they indeed are) be identified?
I'm not sure if this has been done, but we do have samples of instances where genetic incompatibility has been observed to result following population isolation and subsequent evolution. Thus we know that genetic incompatibility does occur at some point in some cases of speciation.
We also know that full incompatibility is not necessary. Take horses and donkeys and zebras as an example: they can form hybrids, but the hybrids are so rarely fertile\fecund that for all intents and purposes the gene flow is stopped with the deaths before reproduction of the hybrids.
My concern here is that if we do not have genetically incompatable 'species' it would call into question that NS could break that "barrier".
Before we can talk about breaking a barrier, we would need to show that one exists. NS is opportunistic: it takes the opportunities provided by mutations and matches them to the opportunities provided by ecologies to select individual phenotypes that are best suited to survive and reproduce within the ecologies. As new mutations are added to the mix, more possibilities open up for evolution in general, and natural selection in particular, to take advantage of.
By this means, an arm can develop into a wing, or a skin flap can develop into a gliding surface. We see from convergent evolution that similar adaptations to fit the same ecology can occur in diverse lineages.
quote:In this module, you learned that homologies are traits that different lineages inherited from their common ancestor. Homologies are evidence that different species shared a common ancestor. Analogies, on the other hand, are similar traits that were not inherited from a common ancestor but that evolved separately. Analogies often exist because two different lineages became adapted for similar lifestyles.
Sugar gliders and flying squirrels look amazingly similar. They are both furry animals of about the same size, with big eyes and a white belly. And they both glide from treetops using a thin piece of skin that is stretched between their legs. This piece of skin helps keep them stable while gliding.
If one of these can evolve from a placental squirrel, and the other evolve from a marsupial possum, then one has to wonder what kind of barrier can exist to block evolution.
Enjoy.
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