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How would we know that we have evolved - A question about speciation.

by BenG549
Tags: have evolved, speciation
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Jan15-13, 07:26 PM
P: 70
I've noticed a few questions in the biology section of PF regarding human evolution. Most of them are about whether we have stopped evolving, or whether our medical knowledge and intervention has slowed down the evolutionary process etc.. Most of these are easily answered by reading the 'introduction to evolution' posted by Ryan_m_b*** but I'm not sure it discusses this (although I might have missed something).

At least conceptually I understand the process of evolution and I understand that "development" in an evolutionary sense does not mean speciation and there are examples of human evolution that don't constitute "a new species" but I'm interested in how we would establish if we had in fact reached a divergence in the evolutionary process i.e. speciation had occurred.

From what I understand the most widely used technical definition defining the difference between species is an inability to breed (at least with the production of fertile offspring)?... I guess it's convenient in that respect that we aren't asexual... but even so I read* that in most cases, the biological speciation concept cannot be practically applied to delimit species, partly because of the extent to which you would need to test breeding in potentially divergent species.

Anyway, I guess my question is how would we establish whether we (a section of our global society) had diverged enough from "our ancestor" in order to limit to possibility of fertile offspring.

I assume that of the different types of geographic speciation, due to our geographical mobility, Sympatric speciation** is the only one that is likely to effect us? But in the event of speciation will we just observe a slow rise in the failed use of fertility treatments?, are there any other widely used cues that separate species other than the ability to produce fertile offspring? (The link I included* mentions a few different concepts but having not formally studied biology to any real academic level I'm not sure how widely accepted or used they are), is this a stupid question lol?

Biology is obviously not my forte, so there is probably a simple answer or qualifying point that I am missing. Although it's biology, so by simple answer I probably mean "In most cases.... however" or " It is somewhat accepted... but"

Anyway I've skim read the links posted by Ryan_m_b but I couldn't see an answer to this, if I missed anything obvious let me know. Otherwise any knowledge or insight would be appreciated.



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Jan15-13, 08:29 PM
Sci Advisor
P: 8,779
In general, there are many problems with a strict definition. It should not be expected to hold at a very fine level, in the same way that the concept of an atom is a good approximation in everyday life, but not at very high energies. Maybe try Coyne's review as an informed viewpoint to start your search on the subject (one of the links at the top right should lead to a free version of the article).

On the usefulness of a "species" concept:
"Any discussion of the genetics of speciation must begin with the observation that species are real entities in nature, not subjective human divisions of what is really a continuum among organisms. We have previously summarized the evidence for this view and counter-arguments by dissenters (Coyne 1994). The strongest evidence for the reality of species is the existence of distinct groups living in sympatry (separated by genetic and phenotypic gaps) that are recognized consistently by independent observers."

On various definitions of "species":
"Like most evolutionists, we adopt the BSC as the most useful species concept, and our discussion of the genetics of speciation will accordingly be limited to the genetics of reproductive isolation. We recognize that this view of speciation is not universal: systematists in particular often reject the BSC in favour of concepts involving diagnostic characters (Cracraft 1989; Baum & Shaw 1995; Zink & McKitrick 1995). We have argued against these concepts elsewhere (Coyne et al. 1988; Coyne 1992a, 1993a, 1994) and will not repeat our contentions here."

From his discussion:
"First, the field has grown increasingly genetical. As a consequence, a large body of grand but notoriously slippery questions (How important are peak shifts in speciation? Is sympatric speciation common?), have been replaced by a collection of simpler questions (Is the Dobzhansky-Muller model correct? What is the cause of Haldane's rule?). Although it would be fatuous to claim that these new questions are more important than the old, there is no doubt that they are more tractable. Second, the connection between theory and experiment has grown increasingly close. Whereas speciation once seemed riddled with amorphous and untestable verbal theories, the last decade of work has produced a body of mathematical theory yielding clear and testable predictions about the basis of reproductive isolation. Last, but most important, many of these predictions have been tested. Despite this progress, many questions about speciation remain unanswered."
Jan15-13, 09:02 PM
Sci Advisor
P: 8,779
A somewhat different discussion of the issues is provided by Avise and Wollenberg.

"A recent criticism that the biological species concept (BSC) unduly neglects phylogeny is examined under a novel modification of coalescent theory that considers multiple, sex-defined genealogical pathways through sexual organismal pedigrees. A competing phylogenetic species concept (PSC) also is evaluated from this vantage. Two analytical approaches are employed to capture the composite phylogenetic information contained within the braided assemblages of hereditary pathways of a pedigree: (i) consensus phylogenetic trees across allelic transmission routes and (ii) composite phenograms from quantitative values of organismal coancestry. Outcomes from both approaches demonstrate that the supposed sharp distinction between biological and phylogenetic species concepts is illusory. Historical descent and reproductive ties are related aspects of phylogeny and jointly illuminate biotic discontinuity."

Jan16-13, 07:40 AM
P: 605
How would we know that we have evolved - A question about speciation.

You might also want to read this amazing post made by Bobze on the topic.

Quote Quote by bobze View Post
Think about it like this (I find this analogy always helps people). Suppose I had this color bar representing an evolutionary lineage:

Now suppose I asked you to draw a line between red and orange. Where you draw the line and where I draw the line will probably be at two different RGB values. The reason being of course, the change from the "red species" to the "orange species" is very subtle--Its not a "click and where there" kind of thing. Rather it is an extremely gradual change in RGB values where a single pixel line (a "generation") is essentially (to us visually anyway) indistinguishable from the next.

Likewise, "species" are the same way. The variation vertically in any one generation, is typically less than what is found within the population at large. Therefore, from parent to offspring (generation to generation) the distinction between "species" doesn't actually exist.

It only exists because the fossil record is incomplete (for example, we may have many "in between" generations missing between red and orange) and we are observing it in hindsight. Because of the incompleteness artefactual "divisions" can exist in a lineage--Which we call "species".

Consider another thought experiment put forth by Dick Dawkins. Which addresses the problems with the "biological species" concept and evolutionary lineage historicity.

Suppose you and I have a time machine and were off to collect historic ancestors in a manner rivaling the Victorian rape of the natural world. The ol' snatch and grab.

Suppose we dial our flux capacitor back to 10,000 BC and hop back through time.

Abducting a person then bring them back to our future. In our sick experiment, we convince a modern individual to breed to this person from an ancestral population and see what happens.

Probably, we get offspring. So according to the biological species concept (we can interbreed--Simplified) we are of the same "species" as the individual from 10,000 BC.

No suppose we repeat our foray into history many times, hopping back in 10,000 year intervals. Eventually we run into an individual, well call individual X that cannot interbreed with us. So have we found an objective measure of our "species" its "ultimate origin"?

Consider the individual we abducted before X, we'll call Y. Individual Y, who we can interbreed with and is therefore "of our species" could very, very likely interbreed with individual X. In other words, individual Y's "X" is not the same as our "X", though both us and Y and still interbreed.

How then, can we have found a finite boundary to our species, when members we consider our "species" can interbreed with those "not of our species", while we cannot?

Species, much to the discomfort of even many professional biologists, aren't real tangible things---Lineages and populations are.

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