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Author Topic:   How do we know about natural selection? (Igor and Lithodid-Man only)
Lithodid-Man
Member (Idle past 1831 days)
Posts: 504
From: Juneau, Alaska, USA
Joined: 03-22-2004


Message 10 of 43 (298379)
03-26-2006 5:23 PM


Igor,

I hope that I can answer some of your questions regarding natural selection. From what I have read in your other posts you have a lot of questions and a willingness to listen.

First of all I want to define natural selection. In biology we often refer to natural selection in terms of "forces" but it is important to recognize that these are not forces as are discussed in physics (gravity, etc). Selection is a mechanism rather than a persuasive invisible force.

Natural selection is based upon several observable characteristics of living organisms.

1) Most individuals in a population are different. With the exception of clones and identical twins (even these can vary) individuals have different genetic characteristics. Some of these are mutations, some just different combinations of traits.

2) Not all members of a population will reproduce as successfully. Some will die before reproducing. Some will mate less often or be able to raise fewer offspring.

Numbers 1 & 2 are tied together because #2 is non-random. Some of the differences in #1 may lead to differential reproductive success. If this happens then the difference may be weeded out OR may spread. This is the elegance and beauty of natural selection.

Darwin relied heavily on the concept of artificial selection in formulating natural selection. A farmer or breeder will select only certain individuals to reproduce. The wooliest sheep, the fattest pig, the most obedient dog, etc. What Darwin saw was that in nature it wasn't human choice limiting reproduction but competition for resources, for mates, etc.

I look forward to this discussion and will try to answer any questions you might have. -LM


Doctor Bashir: "Of all the stories you told me, which were true and which weren't?"
Elim Garak: "My dear Doctor, they're all true"
Doctor Bashir: "Even the lies?"
Elim Garak: "Especially the lies"

Replies to this message:
 Message 13 by igor_the_hero, posted 03-26-2006 9:32 PM Lithodid-Man has responded

  
Lithodid-Man
Member (Idle past 1831 days)
Posts: 504
From: Juneau, Alaska, USA
Joined: 03-22-2004


Message 14 of 43 (298512)
03-27-2006 2:50 AM
Reply to: Message 13 by igor_the_hero
03-26-2006 9:32 PM


Great question!
Igor,

Great question! I will do my best to answer what natural selection is.

First, what is selection? This might sound simple (selection is, well, selecting) but it really isn't. In a biological sense it is selecting those characteristics that are best able to survive given the current circumstances. I apologize for the lengthy example but I hope it illustrates my point. Please bear with me on this!

Here is a real world example. Dandelions are common weeds in lawns. If you look at a field of dandelions you can see that they are not all the same. Some are very tall, some are short. Some have leaves that stick up, some have leaves that are flat against the ground. This is natural variability that exists in the dandelion population. If you look at alot of dandelions you may find actual mutations, some with curly leaves, etc.

If you then examine dandelions in a regularlly mowed lawn you find only those that are flat leaved (leaves are level with the ground) and the flowers are on tiny, short stalks. As a scientist you might wonder why are the dandelions this way in the lawn when the ones near the fence or outside the lawn are different (as in normal tall, short, a mixed population).

In science when we observe something we don't understand we form hypotheses. These are ideas that may explain what we see. What makes a hypothesis unique is that it is framed in a way that we can test. Usually a scientist will try to think of all possible explanations that would lead to what is observed. For our dandelion example you might think of these:

1) Dandelions have a means of recognizing a mowed lawn and only produce short offspring in this situation (they only grow as tall as the surrounding vegetation)

2) Dandelions that have been mowed down change their breeding strategy so that future offspring are short (they can adapt to environmental changes)

3) Tall dandelions and their genes became extinct in the lawn because only short ones survived the mowing

After outlining these ideas as a scientist you would then think of experiments to test them. You are not trying to prove them, you are trying to disprove them.

So for #1 you might transplant dandelions (or plant seeds) from the lawn to an unmowed habitat. If the plants or offspring grow tall then you didn't PROVE #1 but you did fail to disprove it. As it turns out the offspring are just as short as their parents in the lawn, so you now reject #1.

For #2 you might do a repeat experiment. Plant your mowed dandelions in an unmowed field and see their height. You also might take an tall dandelion crop and mow it to see if the next crop are short. As it turns out the mowed dandelions produce short offspring and the tall ones continue to produce tall offspring, no matter how many generations you mow them.

For #3 you could take seeds from your lawn samples and seeds from your unmowed samples and grow them in an experimental plot. If they both grow tall (or short), then you disprove #3. If the tall seeds grow tall and your lawn seeds are short, then you again failed to disprove #3. As it turns out this is the result that is seen.

Now in your dandelion experiment you have the following results:
#1 - unlikely
#2 - unlikely
#3 - not disproven

Because #3 is not disproven you might think of other experiments to test it further. But in this case let's pretend this is the end and you go with number 3 as the answer to the big question, "why are dandelions in mowed lawns short?".

Your experiment demonstrates selection. Only those dandelions that carried the genes for flat leaves and short flowers survived to reproduce. Out of the millions of dandelion seeds that blew into the lawn, only the shortest were able to have offspring in that environment (remember, the ones nearby were tall and normal). If someday the house went unsold and no one took care of the lawn anymore this could change. The grass could grow and shade the short dandelions. Only those mutants in the 'short' gene pool that were slightly taller could survive to reproduce. Eventually their descendents would look very much like the original types, tall and with upright leaves.

This is natural selection, even though it is a human-caused environment. In place of dandelions think of deer with thick and thin coats living in a valley. If the climate changes to cooler those with thicker coats may have an advantage. They have more offspring and soon the whole population carries the gene for thick coats.

The important point to keep in mind is that selection is ONLY for the current environmental conditions. And several different traits may be selected for at the same time, sometimes in different directions. This is why we see variation in selected traits.

I again apologize for the length of this post, please feel free to ask questions. -LM


This message is a reply to:
 Message 13 by igor_the_hero, posted 03-26-2006 9:32 PM igor_the_hero has responded

Replies to this message:
 Message 15 by igor_the_hero, posted 03-27-2006 5:04 PM Lithodid-Man has responded
 Message 43 by westernjoe, posted 01-09-2007 5:04 PM Lithodid-Man has not yet responded

  
Lithodid-Man
Member (Idle past 1831 days)
Posts: 504
From: Juneau, Alaska, USA
Joined: 03-22-2004


Message 16 of 43 (299362)
03-29-2006 1:41 PM
Reply to: Message 15 by igor_the_hero
03-27-2006 5:04 PM


Re: Great question!
Hi,
Sorry for the delay in response but this week is full. I will write a short bit here then hopefully more later.

Ok, I understand you. I think. But how would you prove it?

This is one of the points in science that most people (even some scientists!) find confusing. Science never 'proves' anything. Are you familiar with the Sherlock Holmes axiom "It is an old maxim of mine that when you have excluded the impossible, whatever remains, however improbable, must be the truth" ? This is close to how science operates.

Let's say that you have published your paper on dandelions, strongly suggesting that your #3 is supported (remember, we 'excluded the impossible' by disproving #1 & 2). Years later, another researcher makes a new discovery that ant poison can make plants stunted in growth. After reading this you realize that you did not eliminate all other possible answers, there is a #4 hypothesis you didn't think of because the principle was unknown when you published. If you believe that it is another possible solution you might redo your experiments but add another, one that would disprove #4 if it were impossible.

This is how science works (in part, I haven't discussed the predictability aspect yet). This is also why new discoveries in all of the sciences can lead to a flurry of activity as scientists check their findings against the new findings.

What we use instead of proof in science is this idea of predictability. Your dandelion paper was about one particular lawn you studied. But your principle should apply to all dandelions in a ll lawns. In essence you are saying, "If hypothese 3 is correct I predict that dandelions in any mowed lawn will be shorter than their cousins in unmowed habitat".

The very next day another researcher could look at his well-mowed lawn with tall dandelions and say, "Nope, not in my lawn". This doesn't disprove your hypothesis (doesn't strengthen it either neccessarily) as there could be a number of factors involved. Maybe his mower doesn't a have a bag so the tall seeds are scattered back onto the lawn while yours are hauled away to the dump and so on. You would then devise ways to test more hypotheses.

The important this to remember though is even if 100 researchers examine 1000 lawns and everyone of them conforms to your prediction, you still haven't proven anything. Your work is very strongly supported. You might say with 99.9% confidence that the next lawn (number 1001) will also have short dandelions. Again if it doesn't you don't toss out your whole idea, you search for reasons behind the exception.

Also, when you are selecting, you have to have a selector, correct?

Well yes and no. There has to be something selecting but that doesn't have to be intelligent. In the case of a dog breeder the selector is the breeder. In the case of the dandelions the selector is the mower. But again picture a population of deer that live on a mountain slope. Those with thin coats do no not survive the winter as frequently as those with thick coats. In this case it is only the climate that is the selector. So basically, from a biological standpoint, your 'selector' is just the environment and environmental factors.
The dog-breeder is consciously selecting what they want in the next generation. The lawn mower or the climate are not choosing intelligently what traits will be in the next generation but the effect is the same (some will survive, some will not).


This message is a reply to:
 Message 15 by igor_the_hero, posted 03-27-2006 5:04 PM igor_the_hero has responded

Replies to this message:
 Message 17 by igor_the_hero, posted 03-30-2006 4:03 PM Lithodid-Man has responded

  
Lithodid-Man
Member (Idle past 1831 days)
Posts: 504
From: Juneau, Alaska, USA
Joined: 03-22-2004


Message 18 of 43 (299737)
03-31-2006 5:07 AM
Reply to: Message 17 by igor_the_hero
03-30-2006 4:03 PM


Re: Great question!
But in your example about the deer, you couldn't really consider the environment. A lot of animals migrate so that they can survive.

Great point! Think about this, there may be many possible solutions to an environmental condition. Heavier fur, a tendency to migrate, an ability to hibernate, all off these are possible solutions to a changing cold environment. Depending on the species each may preferred.

For a species such as a deer migration may be the best solution. Picture a population of deer in a relatively protected valley (winters are fairly mild, lots of food, etc). If there is a series of colder winters over several years the protected valley becomes a harsher place, at least during winter months. Those individuals who by habit wandered towards better forage during the winter (even when it was 'nice' still in the valley) would surivive better and have more offspring. As the climate changed and winters in the valley became harder, they already had the tendency to seek better forage and would therefore do better. Every spring when these 'wanderers' came back to the rich valley they might find fewer and fewer of their group alive, or, even if alive, not as healthy and able to produce offspring. In a short time bucks would find themselves competing for mates with starved, scraggly competitors. It doesn't take many generations until we would see that all of the deer in this population are migrating out of the valley during the winter and returning when it is spring. The trait for migration has been selected!

Here is another scenario with the same deer. Let's say that the valley they live in is actually the best around. Even when the climate has changed over years there is nothing better nearby, in fact the forage is worse during the winters then the crappy forage they have in the valley. In this population the wanderer's do even worse than the one who stay behind and deal with it. They might only last a few winters before the wander gene is extinct. But of those that wait out the winter the ones who have traits that allow them to do better may survive. This could be thicker fur. This could be those that had a tendency to over-eat during the fall and had thicker fat. Maybe both of those types would do better and have more offspring. We might expect to see this population tending towards those individuals that BOTH stored fat and grew a winter coat (the two types would both survive, both reproduce, within the same population).

I live on Baranof Island in Alaska. Here our native deer are called Sitka Black Tail. In reality they are mule deer. I don't know your familiarity with deer, but mule deer are huge. Generally over 200 pounds for bucks (and up to 300 pounds or more). Our Sitka Black Tail (I am in Sitka) GET TO 120 pounds and are usually 80 - 100 pounds for bucks. They are tiny deer. The first time I saw a hunter carrying one out of the woods I thought it was terrible they shoot fawns here. As it turns out the reason they are so small is they are forest deer. Our winters are fairly mild, and open grassland simply doesn't exist (we have peat bogs instead of grassland or fields). These deer live and forage in thick brush during the fall, summer, and spring. Better to be small. During the winter they scrape and forage in the old growth or on the beach. Again better to be small. Small but soooo delicious.

Anyway, I hope this makes sense. Deer and dandelions are just examples. If you want to blow your mind think that there are over 10 million species on this planet, and each of them have an environment that changes. For each of those there are different potential adaptations, different solutions. Only some of the offspring of those millions will survive. Some will find one way to live, others another, others will become extinct. Something to ponder....


This message is a reply to:
 Message 17 by igor_the_hero, posted 03-30-2006 4:03 PM igor_the_hero has responded

Replies to this message:
 Message 19 by igor_the_hero, posted 04-01-2006 12:47 AM Lithodid-Man has responded

  
Lithodid-Man
Member (Idle past 1831 days)
Posts: 504
From: Juneau, Alaska, USA
Joined: 03-22-2004


Message 20 of 43 (299986)
04-01-2006 1:37 AM
Reply to: Message 19 by igor_the_hero
04-01-2006 12:47 AM


Re: Great question!
Then your deer go extinct because the aren't adapted to the changes that take place in the disaster. Would that be considered natural selection?

Yes, it would. But in this case selection occured without evolution. Sometimes there are no survivors, no 'winners'. Evolution (change) can only occur when the selection process leaves survivors that may pass on the trait the helped them survive. Also, there are some disasters that take out the fit and the unfit. In the deer example it could be a fire. No mutation, no adaption in deer makes them fireproof. Keep up the good questions!


This message is a reply to:
 Message 19 by igor_the_hero, posted 04-01-2006 12:47 AM igor_the_hero has responded

Replies to this message:
 Message 21 by igor_the_hero, posted 04-01-2006 8:57 AM Lithodid-Man has responded

  
Lithodid-Man
Member (Idle past 1831 days)
Posts: 504
From: Juneau, Alaska, USA
Joined: 03-22-2004


Message 22 of 43 (300469)
04-03-2006 2:07 AM
Reply to: Message 21 by igor_the_hero
04-01-2006 8:57 AM


Re: Great question!
Does natural selection ever have any unexplained changes?

I think I understand (based on your next question) what you are saying. But your question is incorrectly worded. You might think of it in terms of "Can natural selection account for adaptation for a trait that might be solved by a simpler adaptation?" If that is confusing I hope I can explain using your example.

I mean like the chaemeleon. There are plenty of animals out there that are camoflauged without having to change colors.

I am going to start by telling you that I am not a squamatiid (lizards and snakes) expert, my area is in invertebrates. But I know a bit and have some references on hand. As I understand it lizards are split into two groups, Iguania (Iguanas, Old World Iguanas, and Chameleons) and Scleroglossa (all other lizards and snakes).

One of the traits found throughout the Iguanids is the ability to pump melanin (dark pigment) within their cells of the third skin cell layer. The second cell layer is yellow, the first is blue. So in most iguanids the default (no change) color is green (blue top layer + yellow under layer). By pumping melanin (black) towards the surface they are able to change skin color from green to nearly black. Red is produced by capillaries (blood) near the skin surface.

How this evolved? Mystery to me. Because as a group their default color is green, it might make sense that individuals who had the ability to hide their greeness in conditions with a different background color might have prevailed. Those green individuals with more melanin in the third skin layer might have survived better that those that were green, changing to a brown skin color. Later it might be that those individuals with the ability to simply change from green to brown did better than those that were only brown. From there who knows? I will look around and see if I can find any tested hypotheses on the development of color changing ability in reptiles. I do know that a number of these lizards, including chameleons, use skin color and pattern to attract mates and frighten off rivals.

The important point is that we have multiple tools in science for answering these questions. Physiologists can examine the cells and tell us HOW the color change works. Geneticists and taxonomists (those that classify organisms) can look at lizards and tell us which are closely related and which are not. Behavioral ecologists can look at how color change is used. Together we can construct a plausible outline for how the ability came to exist in its amazing modern form.


This message is a reply to:
 Message 21 by igor_the_hero, posted 04-01-2006 8:57 AM igor_the_hero has responded

Replies to this message:
 Message 23 by igor_the_hero, posted 04-03-2006 4:22 PM Lithodid-Man has responded

  
Lithodid-Man
Member (Idle past 1831 days)
Posts: 504
From: Juneau, Alaska, USA
Joined: 03-22-2004


Message 24 of 43 (301232)
04-05-2006 3:58 PM
Reply to: Message 23 by igor_the_hero
04-03-2006 4:22 PM


Re: Great question!
Hi Igor,

Clearing a rainforest is not itself natural selection but an environmental change that may allow selection to occur. Remember, selection is a)differences in organisms and b)those differences allow some types to do better than others. One common cause of selection is environmental change and this can be rainforest destruction.

What is unique about our destruction of the forests is the speed and scale. If the forests were shrinking in size due to long-term climate change (as has happened before) then many species would be able to adapt. Few species can adapt sufficiently to survive massive change within a decade or less. Selection can only operate on those traits that appear in the population. For rainforest animals they have to not only face a lack of trees but other species that are already adapted to open areas. It is possible, even probable, that some rainforest forms will adapt. But most will either die or keep retreating with the forest. I remember in Central America seeing parrots begging french fries from a McDonalds. It is possible that those individuals who learned to do this might do better than their fruit-eating relatives who are sticking to the jungle. There are bird species like the rock pigeon (our common pigeon) and the English sparrow that are no longer found 'in the wild' but are exclusively associated with human habitation.

If there are points from my past comments you have questions about, please feel free to do so. As I mentioned before, you ask good questions and that is a really big step in understanding. Take care -LM


This message is a reply to:
 Message 23 by igor_the_hero, posted 04-03-2006 4:22 PM igor_the_hero has responded

Replies to this message:
 Message 25 by igor_the_hero, posted 04-05-2006 4:41 PM Lithodid-Man has responded

  
Lithodid-Man
Member (Idle past 1831 days)
Posts: 504
From: Juneau, Alaska, USA
Joined: 03-22-2004


Message 28 of 43 (301771)
04-06-2006 8:48 PM
Reply to: Message 25 by igor_the_hero
04-05-2006 4:41 PM


Re: Great question!
Is it possible to get natural selection and no change? I mean you have an animal that is poorly suited to its environment. Then a catastrophe changes its habitat to make it perfectly suited to a new one.

Before I start it is important to keep in mind that 'perfectly suited' probably doesn't exist. Very well suited does, but there is always room for improvement.

There are in nature what we refer to as 'pre-adaptations'. These aren't organisms that are poorly adapted to a particular environment. But they have a trait that allows them to exploit a new environment (or a changed one) immediately, with little change to themselves. One example that comes to mind is that of the rock pigeon (the common pigeon). They traditionally nest in holes on cliff faces, a relatively uncommon (at least overall) habitat. But this habit made them able to move right into human cities as we create lots of vertical faces with holes. Now this species is found world-wide and in vast numbers. The ancestors were pre-adapted to raising young in a particular habitat, one that was patchy in distribution. Then along comes a species that not only wastes a lot of food but also creates this habitat en masse.

I am trying to think of other examples, I will keep thinking about it. Take care- Aaron


This message is a reply to:
 Message 25 by igor_the_hero, posted 04-05-2006 4:41 PM igor_the_hero has responded

Replies to this message:
 Message 29 by igor_the_hero, posted 04-06-2006 8:57 PM Lithodid-Man has responded

  
Lithodid-Man
Member (Idle past 1831 days)
Posts: 504
From: Juneau, Alaska, USA
Joined: 03-22-2004


Message 30 of 43 (301817)
04-07-2006 3:06 AM
Reply to: Message 29 by igor_the_hero
04-06-2006 8:57 PM


Waiting for mutation

What if you get natural selection and no mutation? If you have to wait billions of years for a helpful mutation, wouldn't natural selection cause the species to go extinct?

Bingo! You have hit on a critical point in evolution. Because natural selection operates on mutations, changes have to coincide with the selection event. This is why slow changing environments favor species adapting and changing while environments that change very quickly are likely to lose most if not all of their species.

One important point, however, it doesn't take billions of years for helpful mutations to occur. Most mutations are neutral (and neutral mutations may be beneficial or harmful in the new environment). Every living being on the planet has some mutations (every human has at least several!). The vast majority of these mutations will never be observed and will simply persist in the background or go extinct over generations. But sometimes a slight (or even great) advantage will be conferred. When the presence of one of these coincides with environmental change, we might then see that trait undergo further selection in future generations. Eventually the descendents are very different from their original type.


This message is a reply to:
 Message 29 by igor_the_hero, posted 04-06-2006 8:57 PM igor_the_hero has responded

Replies to this message:
 Message 31 by igor_the_hero, posted 04-09-2006 10:02 PM Lithodid-Man has responded

  
Lithodid-Man
Member (Idle past 1831 days)
Posts: 504
From: Juneau, Alaska, USA
Joined: 03-22-2004


Message 32 of 43 (304156)
04-14-2006 6:22 AM
Reply to: Message 31 by igor_the_hero
04-09-2006 10:02 PM


Extinction
Sorry for the delayed response. This has been a very hectic few days.

I understand! I am also very busy and apologize for this delay.

What I am asking is why aren't animals going extinct when we are changing the environment so rapidly?

Your question is complex and I do not have all of the answers. First and foremost, extinction is occuring at a rapid rate. What is important to remember is that extinction in a human sense and extinction in a 'real world' sense may be different things. We call a species extinct when all known members of that species are no longer in existence anywhere. That would be a human definition. This occurs at a frightening rate as we alter critical habitat types.

But what is ultimately more destructive is local extinction. We kill off a population of organisms in a given region. A species might be in existence in region A and region C, but every individual in region B is gone. This limits A & C each to their own potential mutations (assuming that those individuals in region B were between the other two). Without that extinction an adaptation in A, B, or C could have spread to the other two. By eliminating B we didn't just take 1/3 of the variation out of the population we took 2/3 from both A and C. This is called fragmentation, and is a HUGE problem in conservation biology. Think about it, we rarely destroy all of a particular habitat, we like to set aside parcels of 'pretty' land. Those parcels may be too far apart for most species to cross.

As far as air pollution, I think in reality it is (at least at this time) fairly localized. Most areas of the planet don't have to deal with the smog of LA, Tokyo, etc. That pollution is having an effect everywhere, but the change is slow in most of the terrestrial biomes. I am very much an environmentalist, but also try to have the scientific background to look at multiple environmental issues. A single volcano can cause local extinctions for thousands of square kilometers around it and change climate for decades. The point is that species are adaptable. Life survived a comet that put the entire planet into an ice age (the end of the Cretaceous). Even more amazing (as an invertebrate zoologist) is the Permian event where over 90% (actually calculated at 96%!) of life on this planet was wiped out by an unknown factor (probably multiple factors).

Humans in the last few centuries are changing the planet at an alarming rate. Countless species are going extinct and some are adapting. Where this differs from historical events is that we can recognize and stop some of this from happening.

Honestly though, and I enjoy my soapbox, I need to keep this to the topic. I welcome any questions regarding our past topics or any new ones relating to evolution or natural selection. Thank you for the great question. - Aaron


This message is a reply to:
 Message 31 by igor_the_hero, posted 04-09-2006 10:02 PM igor_the_hero has responded

Replies to this message:
 Message 34 by igor_the_hero, posted 04-15-2006 2:29 PM Lithodid-Man has responded

  
Lithodid-Man
Member (Idle past 1831 days)
Posts: 504
From: Juneau, Alaska, USA
Joined: 03-22-2004


Message 35 of 43 (304493)
04-15-2006 7:24 PM
Reply to: Message 34 by igor_the_hero
04-15-2006 2:29 PM


Evolution is a fact
Igor,
This gets heavy into the nuts and bolts of science. When dealing with evolution it is important to separate fact from theory. The FACT of evolution is that organisms change, new species arise, etc. This is observable and supported by a large number of independant observations from different scientific disciplines (genetics, morphology, paleontology, etc). The THEORY of evolution is an attempt to explain the mechanism by which evolution occured. Facts are what we can observe or infer, theories are attempts to explain mechanisms.

A suitable analogy comes from the dandelion example:
FACT: Dandelions in the mowed lawn are short.
THEORY: Dandelions are short because mowing selected those with short genes.

Another example of this is gravity. You have heard of the Theory of gravity, I assume. So, why is gravity a theory when you can drop a brick and watch it fall? Shouldn't it be a proven fact? In this case the brick falling is a FACT. It is proven that bricks fall everytime. The theory is why that happens or by what rules it happens. Isaac Newton derived an equation that describes the attraction of masses. So far his equation has not been refuted, everywhere we look we see the same relationship. As to what causes gravity there are a number of theories (I am not familiar enough with these to even begin to discuss them!) but as I understand it gravity is still something of a mystery.

With evolution the FACT is change in organisms, the THEORY is the mechanism of natural selection. It is possible (although highly unlikely) that we will one day discover a new mechanism that explains the observed changes better than natural selection. It is recognized today that a mechanism called genetic drift can cause changes without natural selection (although these changes are mostly restricted to the non-expressed gene level). Natural selection is strongly supported because it has resisted falsification for nearly 150 years.

The word 'theory' is commonly misused on this topic. Nearly every single creationist source makes the claim "Evolution is only a theory." This is using the word not in a scientific sense but in a popular jargon context. If I wake up and find my shoes chewed I might say, "I have a theory about how this happened." I do not mean that I am going to design experiments, test different hypotheses, etc. I mean, "I have an idea about what caused this". When we say "The Theory of Evolution" we don't mean "We have an idea about how this happened". The ToE refers to a set of hypothese and predictions that have been tested and could not be disproven. Just like the Theory of Gravity, Atomic Theory, etc.


Doctor Bashir: "Of all the stories you told me, which were true and which weren't?"
Elim Garak: "My dear Doctor, they're all true"
Doctor Bashir: "Even the lies?"
Elim Garak: "Especially the lies"

This message is a reply to:
 Message 34 by igor_the_hero, posted 04-15-2006 2:29 PM igor_the_hero has responded

Replies to this message:
 Message 36 by igor_the_hero, posted 04-18-2006 8:34 PM Lithodid-Man has responded

  
Lithodid-Man
Member (Idle past 1831 days)
Posts: 504
From: Juneau, Alaska, USA
Joined: 03-22-2004


Message 38 of 43 (305600)
04-21-2006 4:23 AM
Reply to: Message 36 by igor_the_hero
04-18-2006 8:34 PM


Re: Evolution is a fact
But when you consider theories, what about laws? The Laws of Thermodynamics for example. Those aren't theories, they have been successfully proven.

The term 'Law' in science is actually pretty vague. In a mathematical sense a law might be akin to a proof. Because there are no proofs in science, laws really do not have any meaning. I am not saying that there are no scientific laws, just that they are not readily defined.

For the most part, scientific laws are restricted to absolute relationships that can be defined in simple mathematical terms. Laws of physics, laws of chemistry. The former includes the laws of thermodynamics. These are theories that have been tested so extensively and for so long that we are extremely certain that the equation will predict all future experiments. But they are still not proven.

But what is important to keep in mind is that the concept of a law in science is not something that a panel decides. A law is no different from a theory in a real scientific sense. Most areas of science cannot be defined by a simple equation. This is why most laws are restricted to physics.

You will hear mention of biological laws, such as 'The Law of Abiogenesis'. This has no real meaning. This was dubbed in a different time and in a different context and has no meaning now.

I hope this makes sense - LM


Doctor Bashir: "Of all the stories you told me, which were true and which weren't?"
Elim Garak: "My dear Doctor, they're all true"
Doctor Bashir: "Even the lies?"
Elim Garak: "Especially the lies"

This message is a reply to:
 Message 36 by igor_the_hero, posted 04-18-2006 8:34 PM igor_the_hero has responded

Replies to this message:
 Message 39 by igor_the_hero, posted 04-28-2006 3:57 PM Lithodid-Man has responded

  
Lithodid-Man
Member (Idle past 1831 days)
Posts: 504
From: Juneau, Alaska, USA
Joined: 03-22-2004


Message 40 of 43 (308314)
05-01-2006 7:47 PM
Reply to: Message 39 by igor_the_hero
04-28-2006 3:57 PM


Oxygen
Hi Igor,

You are correct, oxygen was very bad for early lifeforms (and many still living). The earliest abundant organisms were a type(s) of bacteria called cyanobacteria or blue-green algae. It is believed that these changed the world, literally.

At this time there was very little free oxygen in Earth's atmosphere. The oxygen was bound in water molecules and carbon dioxide. The first photosynthetic (actually probably chemosynthetic) organisms were capable of fusing carbon dioxide and water to make simple sugars. The by-product of this is oxygen (same as now). At first this would be no problem as the atmosphere is very big. However, it is thought that after billions of years the atmosphere began to accumulate enough free oxygen that whole groups became extinct. Those that survived (remember, these are bacteria) were those who could tolerate the own waste products the best. Out of those who could tolerate it came those who could actually use this oxygen as an energy source in their cellular processes. Because oxygen is so energetic (gives off a great amount of enery when combined with other atoms) these organisms could do things no prior cells could do. New forms of movement, forming symbiotic relationships, become multicellular, etc.

What is very interesting is how long this took. The earliest life is about 3.8 billion years old. For all but the last 1.7 billion years (less than half) these bacteria were all that there was for life on Earth. For over 4/5 of the history of life there was nothing we would recognize as a plant or an animal by today's standards. Because of this it is thought that life probably arose quickly (as soon as the Earth cooled enough to allow liquid water). But after the first lifeforms arose very little overall change occured for a long time.


Doctor Bashir: "Of all the stories you told me, which were true and which weren't?"
Elim Garak: "My dear Doctor, they're all true"
Doctor Bashir: "Even the lies?"
Elim Garak: "Especially the lies"

This message is a reply to:
 Message 39 by igor_the_hero, posted 04-28-2006 3:57 PM igor_the_hero has responded

Replies to this message:
 Message 41 by igor_the_hero, posted 05-01-2006 8:24 PM Lithodid-Man has responded

  
Lithodid-Man
Member (Idle past 1831 days)
Posts: 504
From: Juneau, Alaska, USA
Joined: 03-22-2004


Message 42 of 43 (310194)
05-08-2006 3:05 AM
Reply to: Message 41 by igor_the_hero
05-01-2006 8:24 PM


Did we stop
Hi Igor,

I am not sure exactly what you are asking. Do you mean have we stopped evolving? To that the answer is no. Every reproducing population is evolving. Even if there is no visible changes, frequencies of genes are changing generation to generation.

About adapting to air pollution in modern times. I think some things are certainly adapting to it. As for us, probably not very much. While the air is polluted in localized areas, nowhere is it so bad that it significantly changes our reproductive rate. It is not outside the realm of possibility that in really bad areas, like Mexico City there could be an increase in smog to the point that it could cause a reduction in survivorship. One possibility could be that those with hemoglobin better able to bind oxygen over carbon monoxide (I assume this is physiologically possible) or better able to unbind carbon monoxide would have more children and we would see people in those regions better able to tolerate pollution.


Doctor Bashir: "Of all the stories you told me, which were true and which weren't?"
Elim Garak: "My dear Doctor, they're all true"
Doctor Bashir: "Even the lies?"
Elim Garak: "Especially the lies"

This message is a reply to:
 Message 41 by igor_the_hero, posted 05-01-2006 8:24 PM igor_the_hero has not yet responded

  
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