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Author Topic:   How do you define the Theory of Evolution?
CRR
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(1)
Message 1 of 93 (811794)
06-12-2017 4:27 AM


We had "How do you define the word Evolution?" but all it has done is show that it can be used many different ways and the thread has become a quagmire. Can we start again with a more restricted version, "How do you define the Theory of Evolution?". Not just change over time, not just the process of evolution, the Theory of Evolution.

Jerry Coyne in "Why Evolution is True" managed to give a definition in one paragraph. So did Kerkut in "Implications of Evolution". Can you give a definition in one paragraph? Some people might need more but try to be as concise as possible.


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Message 2 of 93 (811796)
06-12-2017 9:01 AM


Thread Copied from Proposed New Topics Forum
Thread copied here from the How do you define the Theory of Evolution? thread in the Proposed New Topics forum.
    
RAZD
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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.

Enjoy


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Taq
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(2)
Message 4 of 93 (811819)
06-12-2017 10:42 AM
Reply to: Message 1 by CRR
06-12-2017 4:27 AM


CRR writes:

"How do you define the Theory of Evolution?".

The theory that attempts to explain how species have and continue to change over time.


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CRR
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Message 5 of 93 (811851)
06-12-2017 6:29 PM
Reply to: Message 3 by RAZD
06-12-2017 9:28 AM


Re: The Theory of Evolution ... simple ...
I think that reply is quite good to illustrate the difference between the "process of evolution" and the "theory of evolution".

From (2) I infer that all life began with a single species and your definition therefore includes universal common ancestry. Is that correct?

For accuracy I think this should read "The process of lineal change within species can result in phyletic speciation, or anagenesis." 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.)

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.


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CRR
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Message 6 of 93 (811852)
06-12-2017 6:38 PM
Reply to: Message 4 by Taq
06-12-2017 10:42 AM


Taq writes:

The theory that attempts to explain how species have and continue to change over time.

Looking at domestic dogs we can see how new varieties have been produced over time within the existing species. The species has changed but there has not been a new species.

Your definition is quite consistent with Young Earth Creationism which theorizes that many modern species have been produced by speciation within the created kinds. Actually your definition doesn't even claim that much change. Perhaps I'm more of an evolutionist than you are.


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CRR
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Posts: 578
From: Australia
Joined: 10-19-2016
Member Rating: 1.2


Message 7 of 93 (811853)
06-12-2017 6:57 PM


Theory of Evolution
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.

Many of you will recognize this as a variation of Kerkut's definition of the General Theory of Evolution. It is also a condensed form of the definition Jerry Coyne used in "Why Evolution is True".

The key elements of this are abiogenesis and ascent from a last universal common ancestor (LUCA); both of which I expect to be controversial.


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New Cat's Eye
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Message 8 of 93 (811855)
06-12-2017 8:42 PM
Reply to: Message 6 by CRR
06-12-2017 6:38 PM


Looking at domestic dogs we can see how...

Do you have a different example? Like, a wild one?


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New Cat's Eye
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Message 9 of 93 (811856)
06-12-2017 8:43 PM
Reply to: Message 7 by CRR
06-12-2017 6:57 PM


Re: Theory of Evolution
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.

According to you?


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RAZD
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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.

Enjoy


we are limited in our ability to understand
by our ability to understand
RebelAmerican☆Zen☯Deist
... to learn ... to think ... to live ... to laugh ...
to share.


• • • Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click) • • •

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CRR
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From: Australia
Joined: 10-19-2016
Member Rating: 1.2


Message 11 of 93 (811860)
06-12-2017 9:20 PM
Reply to: Message 9 by New Cat's Eye
06-12-2017 8:43 PM


Re: Theory of Evolution
According to you?

Yes. After all the thread is "How do you define the Theory of Evolution?"
So, how do you define the theory of evolution?
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Meddle
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Joined: 05-08-2006


(1)
Message 12 of 93 (811863)
06-12-2017 11:04 PM
Reply to: Message 7 by CRR
06-12-2017 6:57 PM


Re: Theory of Evolution
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.

This encapsulates what I see as the problem creationists have in trying to describe evolution (this is in a biological context), because creationists view evolution as an opposing theory to the genesis narrative which starts of “in the beginning…”. This results in creationists shunting in abiogenesis and ideas about common ancestry into the theory of evolution because they are coming into it from the opposite direction from Science.

By contrast scientists have to work with the evidence available to them, which both in Darwins time and today is predominately modern species and to some extent the expanding collection of fossilised specimens. So for example they can compare the fully sequenced genome of the tiger and domestic cat and find they are 95.6% similar, as well as calculate the mutation rate giving 10.8 MYA since the species diverged. But this same line of enquiry can be used to compare the human and gorilla genomes and gives a 94.8% similarity, with the populations diverging approximately 8.8 MYA link.

So with the evidence we have from the present we have been able to tunnel into the past to identify how modern species have converged into common ancestors. The existence of fossils providing snapshots of the species which existed at the times of these divergences have been a bonus, a chance to understand the processes involved. This line of evidence does lead to the potential of a LUCA, but it is a consequence of the evidence, not a prerequisite of the theory.

As to the topic I think RAZD’s first example in Message 3 is howI would go about describing evolution. Firstly it describes evolution over generations. There is the obvious distinction over how many generations a feature infers micro or macroevolutionary change. But this also leads into the more subtle idea of fitness. There is a tendency to look at fitness in terms of the individual or the population to define fitness. However, for an individual to be fit it must not just survive, it must contribute to the next generation. The more ‘fit’ an individual is can be determined by how long it is able to survives, how capable it is at mitigating selective pressures such as sourcing food, avoiding predators, recovering from disease; all of which affects the number of offspring it can contribute to the next generation.


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CRR
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From: Australia
Joined: 10-19-2016
Member Rating: 1.2


Message 13 of 93 (811873)
06-13-2017 2:35 AM
Reply to: Message 8 by New Cat's Eye
06-12-2017 8:42 PM


Looking at domestic dogs we can see how new varieties have been produced over time within the existing species.

Do you have a different example? Like, a wild one?

The advantage of using dogs as an example is that we often know the history of a particular breed, and most people are familiar with several different breeds. E.g. During the 1880s, the 3rd Earl of Malmesbury, the 6th Duke of Buccleuch and the 12th Earl of Home collaborated to develop and establish the modern Labrador breed. With wild animals we often don't have that history to refer to. Nevertheless there are some examples.

Researchers in Trinidad relocated guppies (Poecilia reticulata) from a waterfall pool teeming with predators to previously guppy-free pools above the falls where there was only one known possible predator (of small guppies only, therefore large guppies would be safe). In only 4 years the descendants of the transplanted guppies adjusted to their new circumstances by growing bigger, maturing later, and having fewer and bigger offspring.

In the Bahamas, small numbers of anole lizards (Anolis sagrei) were transplanted from an island with tall trees to nearby islands where there were previously no lizards and only smaller bushy vegetation. Body form rapidly changed in succeeding generations. In particular, the relative length of hindlimbs was greatly decreased—thought to be an adaptation for life amongst the twigs of the scrubby vegetation in the lizards’ new habitat.

When Italian Wall Lizards were transplanted from one island to another they exhibited large-scale changes in behaviour (no longer territorial), food preference (went from predominantly carnivorous to vegetarian) and morphology (larger heads and even the production of cecal valves to assist digestion of plants) all in just over 30 years of living in their new environment

We don't know when finches were introduced to the Galapagos Islands but they have diversifies into several varieties to suit conditions there. Although they are often called separate species cross breeding has been observed so they are better described as well marked varieties.

There are more examples if you care to look for them.


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CRR
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From: Australia
Joined: 10-19-2016
Member Rating: 1.2


Message 14 of 93 (811874)
06-13-2017 3:03 AM
Reply to: Message 10 by RAZD
06-12-2017 8:51 PM


Re: The Theory of Evolution ... simple ...
Well I would say it allows for it, but it also allows for multiple common species in the original world, ...

Darwin allowed for a few original forms but made it clear that he favoured only one. Dobzhansky allowed for several original but only one that survived to be the common ancestor. Kerkut and Coyne said one. The current consensus is for LUCA. Of course just because something is the scientific consensus doesn't mean it is correct. While I have used one in my definition you can use several in your's; but for clarity it might be better to say so clearly, because as you can see I inferred incorrectly from what you had written

With anagenesis you have "arbitrary speciation" ...

lack of exchange of genetic material -- the mark of the biological speciation definition.

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.

[With Pelycodus] you have a division into two populations with a gap between them. That gap indicates a lack of interbreeding. Speciation has therefore occurred.

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. This happens with cichlids where several varieties (species?) can live in the same lake but will interbreed if put in an aquarium.
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CRR
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Posts: 578
From: Australia
Joined: 10-19-2016
Member Rating: 1.2


Message 15 of 93 (811875)
06-13-2017 3:22 AM
Reply to: Message 12 by Meddle
06-12-2017 11:04 PM


Re: Theory of Evolution
This results in creationists shunting in abiogenesis and ideas about common ancestry into the theory of evolution ...

If you read Darwin's "Origin of Species" you will find that common ancestry, from one or a few common ancestors, was a core part of his theory. In this I am following definitions given by more than one evolutionist.

Including or excluding abiogenesis is always a point of contention. Again I am following the example of more than one evolutionist. What good is a theory of origin of species that doesn't explain the origin of the first species? However if you are happy to accept the first life was "originally breathed by the Creator into a few forms or into one" then it doesn't matter.

I deliberately did not include mechanisms of evolution or fitness in my definition.

Deal with these things in your own way in your definition, which I look forward to.


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