Sean, it appears to me that your definition of a …

Comment on An apology to PUC by Eddie.

Sean, it appears to me that your definition of a species is more applicable to the Genesis “kind” which, as I recall, was termed a “baramin” by Frank Marsh. Maybe you should use that term instead?

Despite its limitations, the biological species concept works just fine with most vertebrate taxa. There are very many similar or extremely similar taxa that live together in sympatry but never, rarely or occasionally interbreed, demonstrating that they are discrete biological entities–what biologists refer to as species by virtually any definition. If they’re not species, what else would you call them? Maybe your definition is more akin to a genus–which is a subjective taxonomic level although there have been attempts to apply biologically meaningful definitions.

The mere ability to interbreed does NOT define a biological species. A good biological species is not necessarily completely reproductively isolated from other populations. The best criterion is free or random interbreeding among individuals. Occasional interbreeding with another taxon does not mean that they are freely interbreeding. Mallards have hybridized with many different species of ducks, especially in captivity when their choices are limited, but Mallards generally prefer to breed with their own species. Hybrids with other species occur in the wild, but they are relatively rare.

The study of mate choice among two similar taxa living in sympatry (ranges broadly overlapping) or in parapatry (ranges narrowly overlapping) can infer whether they are freely interbreeding. If they randomly mate with either phenotype the populations eventually become intermediate and any phenotypic differences between the two populations disappear. If, on the other hand, most individuals mate assortatively with their own phenotype, the differences between the two taxa are maintained even if some individuals interbreed and produce intermediate offspring. Typically the intermediates are less fit than either parental phenotype, but exceptions (“hybrid vigor”) have been documented in some well documented cases of hybridization. Most wild Mallards look very similar to each other. Ditto with most American Black Ducks, Gadwalls, Northern Pintails, Northern Shovelers, and other species of waterfowl with which they occasionally hybridize. They are all distinct taxonomic units–what we call species, not subspecies or races or varieties of a single species. If they were freely interbreeding those distinctions between the different taxa would eventually disappear.

As for Darwin’s finches, several taxa breed sympatry on each of the larger islands. Although some individuals may interbreed with another taxon, the majority of individuals mate assortatively with their own phenotype, resulting in distinct taxonomic units that are recognized as biological species. They exhibit essential rather than complete reproductive isolation. They are different biological species even though some interbreeding occurs. If they were freely interbreeding with each other on the same island, only one phenotype would be present–but clearly that is not the case. Character displacement is well documented among finches on the islands, as evidenced by less overlap in phenotypic traits between two taxa occurring in sympatry (same island) than between the same two taxa occurring in allopatry (different islands). Clearly a reproductive isolating mechanism of some sort has “evolved” (pardon my science lingo). And a reproductive isolating mechanism could potentially be coded by as few as ONE gene. Speciation–aka macroevolution–can be a relatively simple process. It’s not the same as megaevolution, which I think is what your concept of functional complexity is referring to.

Eddie Also Commented

An apology to PUC
@Sean:

Certain types of birds are certainly notoriously picky about choosing a mate – that’s a given. The choice can hinge on extremely minor differences in appearance or song or even nest building skills. Yet, at the same time, far more striking phenotypic differences, and even unique genetic differences, between various breeds of dogs or even between different human ethnic groups which have been established via some span of reproductive isolation are not classified as different “species”? Why not?

The “striking phenotypic differences, and even unique genetic differences” among different populations of humans and dogs are the results of random mutation, genetic drift, natural selection or (in the case of dogs) artificial selection–not “some span of reproductive isolation.” Humans don’t depend on the color or texture of eyes, hair and skin to avoid mating with chimps or apes, or even different groups of humans. When a female poodle is in heat, it doesn’t matter what “breed” a male dog belongs to, it is equally stimulated and could care less about the length, color or texture of eyes, hair, ears, snout, legs, tail, etc. The reproductive isolating method between dogs (genus Canis) and foxes (genus Vulpes) is likely based on olfaction rather than external morphology.


An apology to PUC
Correction: the author of the citation above is Temple, not Tample.


An apology to PUC
@Sean:

So there are birds who prefer to mate with other birds who have a more “attractive” song? – a song that matches their own particular preference? How is this somehow a basis for species classification whereas more striking differences between human ethnic groups, to include mating preferences, are not?

Song is a reproductive isolating mechanism for many species of birds. Reciprocal playback experiments demonstrate that birds strongly prefer to mate with their own song type. If they don’t want to mate with each other they are reproductively isolated–which is the criterion of the biological species concept. There have been reports of hybrid Alder X Willow Flycatchers but apparently none have been confirmed.

As for humans, numerous studies have demonstrated that genetic variation among human populations is lower than that of most animal species. The genetic evidence indicates that there has never been strong racial differentiation among humans, at least in comparison with that of many non-human animals. A good review of this can be found here:

Tample, A. R. 2002. The genetic and evolutionary significance of human races. Pp. 31-56 in Race and Intelligence: Separating Science from Myth (J. M. Fish, ed.). Lawrence Erlbaum Associates, Inc., Mahwah, NJ.

I suppose there is the potential for speciation in humans to occur as a consequence of assortative mating among racial or ethnic groups, but considerable interbreeding has historically occurred wherever and whenever different racial or ethnic groups lived together, unless it was prevented by culture, which has a strong influence (e.g., miscegenation laws preventing interracial marriage weren’t abolished in the USA until 1967). Maybe assortative mating is based more on culture than biology. Several studies have demonstrated that the degree of assortative mating based on racial or ethnic groups has declined over the past several decades, which is more suggestive of culture than biology. Furthermore, as I mentioned earlier, assortative mating among humans is extremely complex, occurring for both biological and culture factors. Assortative mating occurs for several biological traits besides skin, hair and eye color/texture which we often associate with race and ethnicity, including height, weight and (especially) age.


Recent Comments by Eddie

Changing the Wording of Adventist Fundamental Belief #6 on Creation

SDA Bio Prof: The Bible makes multiple falsifiable prophecies about Nebuchadnezzar conquering Egypt, yet history never records it happening. Does this mean the Bible is effectively falsified?

Sean Pitman: Egyptians had a strong tendency not to record their losses… only their victories.

Sean, does that mean YOU personally believe Babylon conquered Egypt, just as predicted by two prophets? In the absence of any empirical evidence? If the Egyptians didn’t record their losses, why wouldn’t the Babylonians have recorded such a stunning victory?


Southern Adventist University opens Origins Exhibit

Holly Pham: One of the things that has always concerned me is that, according to what I’ve read, birds and reptiles have completely different forms of respiratory systems (flow-through vs. bellows) How is this explained by evolutionists?

Evidence from the vertebrae of non-avian theropod dinosaurs suggests that they, too, possessed unidirectional flow-through ventilation of the lungs. So, according to evolutionary theory, it evolved first in “primitive” non-avian theropods rather than in birds, and comprises one of many shared derived characters supposedly linking birds with more “advanced” theropods. However, I don’t think there is any evidence or even a hypothesis for a step-by-step process of HOW it evolved. Here is a reference:

http://www.ohio.edu/people/ridgely/OconnorClaessensairsacs.pdf


Southern Adventist University opens Origins Exhibit
@Bob Helm: Bob, if you send me an e-mail at sdabioprof2@gmail.com I will send you a pdf file of a 1991 article published by Chatterjee in Philosophical Transactions of the Royal Society B 332:277-342, titled “Cranial anatomy and relationships of a new Triassic bird from Texas.”

Curiously his description is based only on cranial anatomy. I don’t think he ever published an analysis of its postcranial anatomy.


Southern Adventist University opens Origins Exhibit

David Read: Eddie, ecological zonation will yield the same basic order that you’re pointing to: invertebrates appear before vertebrates; fish appear before amphibians; amphibians appear before reptiles; reptiles appear before mammals; reptiles appear before birds, etc.

It could, and it’s the best creationist explanation, but it doesn’t explain why flowering plants were absent from lowland forests. Or why so many land plants appeared before mangroves, which today occur strictly in the intertidal zone. Or why no pre-flood humans have been found. Or, if Sean is correct that the flood ended at the K-T boundary, why many modern groups of birds and mammals (including marine mammals) which first appear during the Tertiary were not buried by the flood.

David Read: The fact that something appears before something else in the fossil record is not proof than anything evolved into anything else.

True.

David Read: You seem to be complaining that God has not made the fossil evidence compulsory, i.e., so clear that no reasonable person can possibly doubt it. And if God hasn’t made the evidence skeptic-proof, then the skeptic is God’s fault, God is responsible for the skeptic.

I’m not complaining. I’m merely pointing out that the evidence can be interpreted in different ways by honest people. And I’m relieved to see that even you don’t think the evidence is crystal clear.

David Read: Only people of faith can be saved, that is, only people who are willing to trust God and put away doubts can be saved.

I agree.


Southern Adventist University opens Origins Exhibit

David Read: Those tracks are so obviously bird tracks that the fact that some scientists want to assign them to “birdlike theropods” is itself a very useful teaching tool as to how the model creates the data.

David Read: That the model actually creates the data is one of the hardest concepts to get across, not only to lay people but even to the scientists themselves.

How does the model affect the data? Data don’t change and they shouldn’t change. It’s the interpretation, not the data, that is affected by the model.