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Author Topic:   How do you define the Theory of Evolution?
CRR
Member (Idle past 697 days)
Posts: 579
From: Australia
Joined: 10-19-2016


(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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CRR
Member (Idle past 697 days)
Posts: 579
From: Australia
Joined: 10-19-2016


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
Member (Idle past 697 days)
Posts: 579
From: Australia
Joined: 10-19-2016


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
Member (Idle past 697 days)
Posts: 579
From: Australia
Joined: 10-19-2016


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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CRR
Member (Idle past 697 days)
Posts: 579
From: Australia
Joined: 10-19-2016


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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CRR
Member (Idle past 697 days)
Posts: 579
From: Australia
Joined: 10-19-2016


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
Member (Idle past 697 days)
Posts: 579
From: Australia
Joined: 10-19-2016


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
Member (Idle past 697 days)
Posts: 579
From: Australia
Joined: 10-19-2016


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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CRR
Member (Idle past 697 days)
Posts: 579
From: Australia
Joined: 10-19-2016


Message 34 of 93 (812919)
06-21-2017 8:03 AM
Reply to: Message 19 by JonF
06-13-2017 8:41 AM


Re: Theory of Evolution
Using RAZD's link and going to "THE ORIGIN OF SPECIES. 6th Ed" p 429

quote:
There is grandeur in this view of life, with its several powers, having been originally breathed by the Creator into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being evolved.

Note Darwin says "into a few forms or into one". Earlier in the book he makes it clear that he favours "one".

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.

I also maintain that the consensus view today is for universal common ancestry as exemplified in Theodosius Dobzhansky's "Nothing in Biology Makes Sense Except in the Light of Evolution".


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CRR
Member (Idle past 697 days)
Posts: 579
From: Australia
Joined: 10-19-2016


Message 35 of 93 (812920)
06-21-2017 8:07 AM
Reply to: Message 31 by Pressie
06-15-2017 5:54 AM


Re: Pressie's definition.
I think that's a reasonable definition. Well stated.

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CRR
Member (Idle past 697 days)
Posts: 579
From: Australia
Joined: 10-19-2016


Message 36 of 93 (812921)
06-21-2017 8:09 AM
Reply to: Message 21 by New Cat's Eye
06-13-2017 10:13 AM


Re: Theory of Evolution
I don't. It is defined by scientific consensus, not us.

Then enlighten me; how is it defined by the scientific consensus?


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CRR
Member (Idle past 697 days)
Posts: 579
From: Australia
Joined: 10-19-2016


Message 40 of 93 (812932)
06-21-2017 10:10 AM


Evolution: The WORD vs the THEORY
The word evolution can have multiple meanings such as;
1. a gradual development [the most basic definition]
2. a gradual development, esp to a more complex form
3. a change in the characteristics of a population of animals or plants over successive generations [biology]
4. a heritable change in the characteristics of a population of animals or plants over successive generations [biology]
5. a change in allele frequency in a population over time [biology: population genetics]

So we can talk about the evolution of language, the motor car, species, or many other things.

But these are all definitions of the WORD evolution and not the THEORY of Evolution (ToE).

We can talk about a theory of Cosmic Evolution or the theory of the evolution of the Solar System but when we say the Theory of Evolution without some addition or qualification it is generally understood as the modern version of Darwin's Theory of Evolution by Natural Selection. (Although I understand Lamark's theory of evolution is making a bit of a comeback with epigenetics)

Of course Darwin's theory has been modified since it was first proposed and some would say that there are today several theories of evolution all derived from Darwin's theory. Darwin made several specific claims in his theory and likewise the modern theory/theories make specific claims.

Darwin took a whole book to discuss his theory and ague his case but many people (e.g. Kerkut, Coyne, Gould, Weintraub) have given definitions of one paragraph or less.

So when I proposed this topic I asked for your definition of the Theory of Evolution. By all means borrow from another source; in which case it is polite to acknowledge it. My definition was a single sentence. Can you give a definition of the ToE in no more than a couple of paragraphs. (If Coyne could manage it I'm sure you can.)


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CRR
Member (Idle past 697 days)
Posts: 579
From: Australia
Joined: 10-19-2016


Message 43 of 93 (812972)
06-21-2017 6:46 PM
Reply to: Message 37 by Tangle
06-21-2017 9:08 AM


Re: Theory of Evolution
the root of the tree of life

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CRR
Member (Idle past 697 days)
Posts: 579
From: Australia
Joined: 10-19-2016


Message 49 of 93 (813259)
06-25-2017 6:46 AM


ToE
RAZD has posted some interesting references from Universities of Michigan and Berkley on the subject at Message 64.

And see my reply at Message 66

To summarise RAZD's sources;

From Michigan we get
Universal Common Ancestry, “Far enough back in time, any pair of organisms shares a common ancestor.”
Abiogenesis, “Life has evolved from non-life, and complex organisms from simpler forms.” This is an assumption prior to rather part of the process of evolution.
Microevolution, “Definition 1: Changes in the genetic composition of a population with the passage of each generation. … [this] “definition emphasizes genetic change. It commonly is referred to as microevolution.”
Macroevolution, “Definition 2: The gradual change of living things from one form into another over the course of time, the origin of species and lineages by descent of living forms from ancestral forms, and the generation of diversity. … [this] “emphasizes the appearance of new, physically distinct life forms that can be grouped with similar appearing life forms in a taxonomic hierarchy. It commonly is referred to as macroevolution.”

Similarly from Berkley
Universal Common Ancestry, “Through the process of descent with modification, the common ancestor of life on Earth gave rise to the fantastic diversity that we see documented in the fossil record and around us today. Evolution means that we're all distant cousins: humans and oak trees, hummingbirds and whales.”
Abiogenesis, they include as an event in “Important events in the history of life”, “Unicellular life evolves. So according to Berkley and Michigan all life evolved from a common microbial ancestor that arose naturally from non-living matter.
Microevolution, is evolution on a small scale — within a single population. That means narrowing our focus to one branch of the tree of life. Biologists who study evolution at this level define evolution as a change in gene frequency within a population.
Macroevolution, generally refers to evolution above the species level.

So both sources appear to agree with what is included in the theory of evolution.

Edited by CRR, : Summary added


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CRR
Member (Idle past 697 days)
Posts: 579
From: Australia
Joined: 10-19-2016


Message 50 of 93 (813397)
06-27-2017 7:41 AM


Jerry Coyne's Definition
As a working definition for discussion purposes I would be prepared to accept the one Jerry Coyne gives in his book "Why Evolution is True"

quote:
"Life on earth evolved gradually beginning with one primitive species—perhaps a self-replicating molecule—that 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." [Jerry Coyne, 2009]

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