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Author Topic:   How do you define the Theory of Evolution?
RAZD
Member (Idle past 1404 days)
Posts: 20714
From: the other end of the sidewalk
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Message 3 of 93 (811799)
06-12-2017 9:28 AM
Reply to: Message 1 by CRR
06-12-2017 4:27 AM


The Theory of Evolution ... simple ...
(1) The process of evolution involves changes in the composition of hereditary traits, and changes to the frequency of their distributions within breeding populations from generation to generation, in response to ecological challenges and opportunities for growth, development, survival and reproductive success in changing or different habitats.
If we look at the continued effects of evolution over many generations, the accumulation of changes from generation to generation frequently becomes sufficient for individuals to develop combinations of traits that are observably different from the ancestral parent population.
(2) The process of lineal change within species is sometimes called phyletic speciation, or anagenesis.
If anagenesis was all that occurred, then all life would be one species, readily sharing DNA via horizontal transfer (asexual) and interbreeding (sexual) and various combinations. This is not the case, however, because there is a second process that results in multiple species and increases the diversity of life.
(3) The process of divergent speciation, or cladogenesis, involves the division of a parent population into two or more reproductively isolated daughter populations, which then are free to (micro) evolve independently of each other.
Both anagenesis and cladogenesis have been observed, (see Pelycodus for example) and thus it is a fact that they have occurred.
(4) The Theory of Evolution (ToE), stated in simple terms, is that the process of anagenesis, and the process of cladogenesis, are sufficient to explain the diversity of life as we know it, from the fossil record, from the genetic record, from the historic record, and from everyday record of the life we observe in the world all around us.
This theory is tested by experiments and field observations carried out as part of the science of evolution. Every new discovery tests this theory.
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RAZD
Member (Idle past 1404 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 10 of 93 (811857)
06-12-2017 8:51 PM
Reply to: Message 5 by CRR
06-12-2017 6:29 PM


Re: The Theory of Evolution ... simple ...
From (2) I infer that all life began with a single species and your definition therefore includes universal common ancestry. Is that correct?
Well I would say it allows for it, but it also allows for multiple common species in the original world, with single cell life forms that can exchange DNA by horizontal transfer -- see Why Horizontal Gene Transfer is a Nail in the Coffin for Continuous Creation -- which is like all the bacteria species having sex, and selection settling on a common pattern (if it works keep it). Roots coming together to form the base of the tree, if you will. There are still a lot of possibilities in the pre-DNA world.
For accuracy I think this should read "The process of lineal change within species can result in phyletic speciation, or anagenesis." ...
I can agree with that. Sometimes it does, sometimes it doesn't, because it is a response to the surrounding ecology. If the ecology is static, selection opts for stasis (because it works and changes mean moving off the mountain peak). If the ecology is changing, selection opts for changes that adapt to the new ecology.
... Change within the lineage could produce a change in the phenotype or different varieties without producing a new species. (Depending of course on the definition of species.)
With anagenesis you have "arbitrary speciation" where some metric is used to say that this observed amount of change is similar to what we see with speciation\cladogenesis. This is done by people specialized in evaluating the skeletal traits and their changes over time, and there is often some dispute on when species should be divided. It is done for ease of reference, though as each population would be judged to be the same species as their parent and offspring generations. Thus species IS hard to define here because the ancestral population no longer exists to judge whether or not they would interbreed.
We've discussed the Pelycodus illustration before and as I have pointed out the resultant variation is less than in modern dogs which are all regarded as one species, so this does not necessarily show either anagenesis or cladogenesis since we can't say if a new species actually formed at any time. The graph is only a plot of tooth size.
Correct, but at the top you have a division into two populations with a gap between them. That gap indicates a lack of interbreeding. Speciation has therefore occurred. This can also be used as a metric for arbitrary speciation, when comparing the differences in their traits.
That the amount of variation is less than observed in dogs does not mean it is not a different species, just that the observed amount of variation is possible with anagenesis (dog breed are isolated breeding populations). In fact, as discussed before, dogs could be considered a ring species. In the wild we would not have as many varieties, as some would meld together and some would disappear, because the selection for dog breeds is artificial and they are protected from natural selection. This would likely divide them up into different species, as wolves and coyotes and foxes are considered different species.
You have a problem with classifying Pelycodus Ralstoni to Notharctus venticolus as all one species AND Pelycodus Ralstoni to Notharctus nunienus as all one species, and then explaining the lack of exchange of genetic material between Notharctus venticolus and Notharctus nunienus -- the mark of the biological speciation definition.
Classification gets messy, because evolution is a continuous process, not a sudden leap. And only humans need classifications to enable technical discussions, the organisms could care less.
But all that is well beyond the topic of defining the Theory of Evolution.
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This message is a reply to:
 Message 5 by CRR, posted 06-12-2017 6:29 PM CRR has replied

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RAZD
Member (Idle past 1404 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 18 of 93 (811886)
06-13-2017 7:30 AM
Reply to: Message 14 by CRR
06-13-2017 3:03 AM


Re: The Theory of Evolution ... simple ...
That depends on your definition of species. There could be geographical, behavioral, or ecological reasons for maintaining separate varieties even though they could still interbreed. ...
Curiously I don't care to much if the can or could interbreed, when we can force camels and llamas to produce offspring, reproductive incompatibility is a questionable metric. What matters is the natural normal behavior -- if the natural behavior is to mate with one group and not another then for all intents and purposes a division in genetic lineages has begun.
And with ring species we see that total genetic isolation is not necessary for the two ends of the ring to normally decline mating with each other. In this regard isolation comes down to sexual selection.
That is all that is necessary for evolution to develop more and more divergence between the populations as generations pass.
... This happens with cichlids where several varieties (species?) can live in the same lake but will interbreed if put in an aquarium.
ie not their natural normal ecology, when the cichlids normally self segregate into different ecological niches, forcing them into a confined one changes their behavior.
Yes species IS hard to define and there are many "species" (and genera) today than can exchange genetic material. If I remember correctly Darwin doubted species as a valid taxonomic unit and thought of a species as a well defined variety. One problem of using "species" in the definition is that you then need to clearly define "species", especially where the meaning can vary.
This is why I prefer cladistics to taxonomy -- taxonomy assumes a static classification (so 18th century), while cladistics only concerns itself with descent from common ancestors; it doesn't care what you call them, it cares what the behavior shows.
We see anagenesis occurring all around us and we see instances of cladogenesis. We see the effects of a continuing changing distribution of traits within breeding populations from generation to generation, and we observe that this ongoing process also explains what we observe in the genetic record and the fossil record.
The ToE explains the evidence.
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RAZD
Member (Idle past 1404 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


(1)
Message 20 of 93 (811898)
06-13-2017 9:15 AM
Reply to: Message 19 by JonF
06-13-2017 8:41 AM


Re: Theory of Evolution
Here's a link on-line to link to the page(s) involved:
Darwin Online: On the Origin of Species
I did a search of the text for "common ancestor" and all that came up was discussion of groups of animals having a common ancestor.
quote:
Book: Darwin, C. R. 1859. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 1st edition, 1st issue. Text Image PDF
... day; and these parent-species, now generally extinct, have in their turn been similarly connected with more ancient species; and so on backwards, always converging to the common ancestor of each great class. So that the number of intermediate and transitional links, between all living and extinct species, must have been inconceivably great. But assuredly, if this theory be true, such have lived upon this earth. On the lapse of Time.Independently of our not finding fossil remains of such ...
Book: Darwin, C. R. 1860. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 2d edition, second issue. Text Image PDF
... have inherited from a common ancestor some advantage in common. Hence, the struggle for the production of new and modified descendants, will mainly lie between the larger groups, which are all trying to increase in number. One large group will slowly conquer another large group, reduce its numbers, and thus lessen its chance of further variation and improvement. Within the same large ...
The search also looked through papers and notebooks and his other books with similar results.
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RAZD
Member (Idle past 1404 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


(1)
Message 29 of 93 (812010)
06-14-2017 7:22 AM
Reply to: Message 5 by CRR
06-12-2017 6:29 PM


Re: The Theory of Evolution ... simple ...
We've discussed the Pelycodus illustration before and as I have pointed out the resultant variation is less than in modern dogs which are all regarded as one species, ...
So you would agree that these also show less variation and could all be one species, yes?
quote:
Figure 1.4.4. Fossil hominid skulls. Some of the figures have been modified for ease of comparison (only left-right mirroring or removal of a jawbone). (Images 2000 Smithsonian Institution.)
(A) Pan troglodytes, chimpanzee, modern
(B) Australopithecus africanus, STS 5, 2.6 My
(C) Australopithecus africanus, STS 71, 2.5 My
(D) Homo habilis, KNM-ER 1813, 1.9 My
(E) Homo habilis, OH24, 1.8 My
(F) Homo rudolfensis, KNM-ER 1470, 1.8 My
(G) Homo erectus, Dmanisi cranium D2700, 1.75 My
(H) Homo ergaster (early H. erectus), KNM-ER 3733, 1.75 My
(I) Homo heidelbergensis, "Rhodesia man," 300,000 - 125,000 y
(J) Homo sapiens neanderthalensis, La Ferrassie 1, 70,000 y
(K) Homo sapiens neanderthalensis, La Chappelle-aux-Saints, 60,000 y
(L) Homo sapiens neanderthalensis, Le Moustier, 45,000 y
(M) Homo sapiens sapiens, Cro-Magnon I, 30,000 y
(N) Homo sapiens sapiens, modern

Or these:
quote:
The story of Bones and Dogs and Humans:
Is the variation in traits seen in the bones between modern humans and Ardi more or less than the variation seen in dogs?
Inquiring minds want to know.
... so this does not necessarily show either anagenesis or cladogenesis since we can't say if a new species actually formed at any time.
Actually the formation of a new species is not necessary for anagenesis, so we do necessarily see anagenesis in the Pelycodus fossils -- they change continuously from bottom to top.
Likewise we do not need to know if Notharctus nunienus and Notharctus venticolus could interbreed to know that the fossil evidence shows that they didn't, and that each population went on to diversify further. So yes, in that regard new species were observed forming.
... less than in modern dogs which are all regarded as one species, ...
In scientific circles that would make you a "lumper" compared to most people that would be "splitters".
quote:
Message 3: (4) The Theory of Evolution (ToE), stated in simple terms, is that the process of anagenesis, and the process of cladogenesis, are sufficient to explain the diversity of life as we know it, from the fossil record, from the genetic record, from the historic record, and from everyday record of the life we observe in the world all around us.
Anagenesis and cladogenesis explain the fossils above. Does your version of the ToE explain them?
quote:
Message 7: The Theory of Evolution is the theory that all the living forms in the world have arisen from a single source which itself arose naturally from an inorganic form.
All I get from that is that all life could be one species ... the ultimate lumping. It doesn't explain the observed nested hierarchies that cladogenesis does, nor the observed change within species over multiple generations that anagenesis does.
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RAZD
Member (Idle past 1404 days)
Posts: 20714
From: the other end of the sidewalk
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Message 32 of 93 (812159)
06-15-2017 6:56 AM
Reply to: Message 30 by dwise1
06-15-2017 4:04 AM


Re: Theory of Evolution
Second, just what is the Theory of Evolution? A theory explains a phenomenon, so the theory of evolution explains evolution. Do you have any idea what that means?
And if the explanation is any good, then you can make predictions for future discoveries.
Those predictions can be used to test the explanatory power of the theory:
If they come true the theory would appear valid, and it can be used for further predictions;
If they don't come true the theory would appear invalid, and a better explanation is needed.
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RAZD
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Posts: 20714
From: the other end of the sidewalk
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Message 38 of 93 (812928)
06-21-2017 9:37 AM
Reply to: Message 34 by CRR
06-21-2017 8:03 AM


Re: Theory of Evolution
So yes I maintain that common ancestry, from one or a few common ancestors, was a core part of Darwin's theory, and the ToE today.
Original common ancestry is an outcrop of evolution, a prediction reached when following the theory and the evidence to a logical conclusion, rather than a foundation. This is what the evidence shows: daughter populations descending from a common parent population, that is also a daughter population descendant from a more ancient common parent population, along with the formation of nested hierarchies. The process of evolution explains how this pattern develops, but it does not require it.
Theories explain evidence, so the ToE explains the evidence of nested hierarchies.
Theories make testable predictions, so the ToE predicts an original common ancestor pool. We test this prediction by looking for new evidence that supports or invalidates it.
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RAZD
Member (Idle past 1404 days)
Posts: 20714
From: the other end of the sidewalk
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Message 70 of 93 (813609)
06-29-2017 8:26 AM
Reply to: Message 66 by CRR
06-29-2017 7:54 AM


Re: Jerry Coyne's Definition
quote:
In essence, the modern theory of evolution is easy to grasp. It can be summarized in a single (albeit slightly long) sentence: Life on Earth evolved gradually beginning with one primitive speciesperhaps a selfreplicating moleculethat lived more than 3.5 billion years ago; it then branched out over time, throwing off many new and diverse species; and the mechanism for most (but not all) of evolutionary change is natural selection.
Looks like a definition to me.
If that is a definition, then what does the theory so defined predict and how can it be tested?
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RAZD
Member (Idle past 1404 days)
Posts: 20714
From: the other end of the sidewalk
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Message 75 of 93 (813717)
06-30-2017 7:06 AM
Reply to: Message 74 by CRR
06-30-2017 3:57 AM


Re: Your Definitions
OK so you don't like my definitions, what's your's?
The Theory of Evolution (ToE), stated in simple terms, is that the process of anagenesis, and the process of cladogenesis, are sufficient to explain the diversity of life as we know it, from the fossil record, from the genetic record, from the historic record, and from everyday record of the life we observe in the world all around us.
where:
quote:
Anagenesis, also known as "phyletic transformation", and in contrast to cladogenesis, is the process in which a species, gradually accumulating change, eventually becomes sufficiently distinct from its ancestral form that it may be labeled a new species (a new form). When this is deemed to occur, no branching or splitting off of new taxa in the lineage is shown in a phylogenetic tree. When no populations of the ancestor species remain the ancestral species can then be considered as being extinct.
Anagenesis is the accumulated effects of the process of evolution within a population over multiple generations.
The process of evolution involves changes in the composition of hereditary traits, and changes to the frequency of their distributions within breeding populations from generation to generation, in response to ecological challenges and opportunities for growth, development, survival and reproductive success in changing or different habitats.
and where:
quote:
Cladogenesis is an evolutionary splitting event where a parent species splits into two distinct species, forming a clade.[1]
This event usually occurs when a few organisms end up in new, often distant areas or when environmental changes cause several extinctions, opening up ecological niches for the survivors. The events that cause these species to originally separate from each other over distant areas may still allow both of the species to have equal chances of surviving, reproducing, and even evolving to better suit their environments while still being two distinct species.[2]
To determine whether a speciation event is cladogenesis, researchers may use simulation, evidence from fossils, molecular evidence from the DNA of different living species, or modelling. It has however been questioned whether the distinction between cladogenesis and anagenesis is necessary at all in evolutionary theory.[3]
Cladogenesis is anagenesis in two (or more) populations that become sufficiently reproductively isolated that they evolve independently of one another.
And example from the fossil record is Pelycodus:
quote:
Pelycodus was a tree-dwelling primate that looked much like a modern lemur. The skull shown is probably 7.5 centimeters long.
The numbers down the left hand side indicate the depth (in feet) at which each group of fossils was found. As is usual in geology, the diagram gives the data for the deepest (oldest) fossils at the bottom, and the upper (youngest) fossils at the top. The diagram covers about five million years.
The numbers across the bottom are a measure of body size. Each horizontal line shows the range of sizes that were found at that depth. The dark part of each line shows the average value, and the standard deviation around the average.
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.
The depth in feet on the left side show relative age, with the oldest fossils at the bottom. The overall trend lines clearly show anagenesis occurring over time, and the split in the populations at the top clearly shows cladogenesis occurring as the two populations diverge from one another. They diverge further after this, becoming classified as new genera, not just new species.
The pattern seen in this fossil record is explained by anagenesis and cladogenesis, thus it supports the Theory of Evolution given above.
The Theory of Evolution predicts that similar patterns will be seen for other species, and the theory is tested by every new find, of a new living species, of a new fossil, and of a new genome record.
The Theory of Evolution predicts that every fossil species found will have an older ancestral species nearby, both in time and in geographic location. This is tested by placing fossils within the temporal spacial matrix where they are found, and comparing them by homologies and shared derived traits with nearby fossils of similar structure. This gets into the science of paleontology as well as evolution.
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RAZD
Member (Idle past 1404 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


(1)
Message 82 of 93 (813850)
07-01-2017 11:03 AM
Reply to: Message 14 by CRR
06-13-2017 3:03 AM


Evolutionary Lineages rather than species?
Yes species IS hard to define and there are many "species" (and genera) today than can exchange genetic material. ...
Ran across this, and thought it might help with your species problem ... they advocate dispensing with "speciation" and "anagenesis" and "cladogenesis" because there is confusion, and instead talk about evolutionary lineages:
quote:
An evolutionary lineage, or line of descent, is the inherent product of evolutionary units replicating in generations over time, and consequently it is a universal feature of all biologically evolving systems (Cutter, 2013). A ‘species’ is therefore always a taxonomic description of an arbitrarily delineated segment of an evolutionary lineage in time (de Queiroz, 1998, 2007; Sites & Marshall, 2003; Podani, 2013; White, 2013).
... ie - a "species" is an arbitrary snapshot of a section of the evolutionary lineage, and it is the lineage that is important rather than the species designation in question.
Now I find their arguments against using anagenesis and cladogenesis to be a little contrived, especially when one take the effort to define the terms when used (for clarity), and a bit over concerned with taxonomy classifications.
They discuss divergence from a parent population as a factor in both anagenesis and cladogenesis
But I also note that they also talk about "cessation of gene flow" rather than genetic incompatibility:
quote:
... The most popular definition of cladogenesis is the splitting of evolutionary lineages (cessation of gene flow), whereas anagenesis is evolutionary change between splits. ...
And they discuss the time frames of which such cessation occurs, and when there is interweaving and hybridization before the process is complete -- ie it is not a single point in time phenomena/event.
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RAZD
Member (Idle past 1404 days)
Posts: 20714
From: the other end of the sidewalk
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Message 84 of 93 (813885)
07-01-2017 7:09 PM
Reply to: Message 83 by caffeine
07-01-2017 5:07 PM


Re: Evolutionary Lineages rather than species?
Cessation of gene flow can take an extraordinarily long time and, unless physical barriers (like oceans) get in the way, can sometimes take place long after populations have become clearly separated from one another.
Curiously, the way I see it is that cessation of gene flow occurs by behavior and sexual selection way before it is genetic incompatibility -- and that this functional cessation of gene flow is all that is necessary ... and that later interactions -- hybridization, and interweaving -- create a mosaic of evolutionary descent that explains a mixture of traits that seem to be 1 from column "A" and 1 from column "B" ...
The article you cite is on the right track, in my opinion. The boundaries between two species are no more meaningful than those between genera and families - they're wholly arbitrary and far too much ink and thought is wasted on them. I think arguing that creationists are wrong because speciation has occurred is a mistake. Speciation has no clear, objective definition.
What we see is a division of an evolutionary lineage into two or more independent lineages, and this easily provides the increased diversity that we see. This occurs through the known evolutionary processes.
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RAZD
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Posts: 20714
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Message 89 of 93 (814112)
07-04-2017 1:58 PM
Reply to: Message 87 by CRR
07-04-2017 6:22 AM


Re: Evolutionary Lineages rather than species?
caffeine writes:
The article you cite is on the right track, in my opinion. The boundaries between two species are no more meaningful than those between genera and families - they're wholly arbitrary and far too much ink and thought is wasted on them. I think arguing that creationists are wrong because speciation has occurred is a mistake. Speciation has no clear, objective definition.
I agree.
Because "species" and "genera" and "family" are just snapshots of arbitrarily selected portions of the lineal heritage of descent for all living and extinct organisms.
We know this lineage with the genetic evidence and the fossil evidence and the evidence of life around us.
As I've said many times before, these names are human inventions used for communication. People love to name things. The reality is the ongoing, ceaseless process of evolution, each generation different from the previous.
How does this affect my definition in Message 3 of the Theory of Evolution?
(4) The Theory of Evolution (ToE), stated in simple terms, is that the process of anagenesis, and the process of cladogenesis, are sufficient to explain the diversity of life as we know it, from the fossil record, from the genetic record, from the historic record, and from everyday record of the life we observe in the world all around us.
If we say that anagenesis is the ongoing, ceaseless process of evolution in a breeding population, and that cladogenesis is ongoing, ceaseless process of evolution in genetically isolated breeding populations, and note that the whole breeding population in anagenesis is genetically isolated, then we can say that
(4) The Theory of Evolution (ToE), stated in simple terms, is that the ongoing, ceaseless process of evolution in genetically isolated breeding populations is sufficient to explain the diversity of life as we know it, from the fossil record, from the genetic record, from the historic record, and from everyday record of the life we observe in the world all around us.
Populations can be isolated by genetic incompatibility (such as you normally find between "species") or they can be functionally isolated by geography or behavior.
The overall meaning is the same, it's just a different way to say it.
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This message is a reply to:
 Message 87 by CRR, posted 07-04-2017 6:22 AM CRR has replied

Replies to this message:
 Message 90 by CRR, posted 07-04-2017 10:04 PM RAZD has seen this message but not replied

  
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