rationalskepticism.org

hackenslash wrote:

CharlieM wrote:Interesting that you think I would see it as weighted towards a correct conclusion.

Not what I said. Read it again.

Why do you think I would see it as such?

Think? No, I know. Why? Because it's the same tired old baggage you bring to every thread. The simple fact is that you want us to be special. We're special in precisely the same way that our place in the centre of the observable universe is special. In short, we're special in precisely the same way that every other species is special, just for different reasons.

Could it be that you also see that we are the beings who they would try to communicate with?

The data support no conclusions as yet.



Food for thought?

hackenslash wrote:

About the difference between us and other animals, from Livescience

There's no consensus on the question of what makes us special, or whether we even are. The biggest point of contention is whether our cognitive abilities differ from those of other animals "in kind," or merely in degree. Are we in a class by ourselves or just the smartest ones in our class?

Charles Darwin supported the latter hypothesis. He believed we are similar to animals, and merely incrementally more intelligent as a result of our higher evolution. But according to Marc Hauser, director of the cognitive evolution lab at Harvard University, in a recent article in Scientific American, "mounting evidence indicates that, in contrast to Darwin's theory of a continuity of mind between humans and other species, a profound gap separates our intellect from the animal kind."

They list these important human abilities which make us unique: 1. Our ability to generate a limitless variety of words and concepts. 2. The way we can combine ideas from different fields. 3. The production and use of mental symbols. 4. Abstract thought.

And the evidence that these are unique to humans is..? At least two of those things are almost certainly not.

hackenslash wrote:

So you don't think that "species" is a very slippery concept and can change according to the whim of humans? I think it is

In deciding whether populations should be treated as species, different ornithologists emphasize different criteria. Some base their decisions on call type, others, on morphology. Many attempt to apply Mayr's definition, or some version of it. There are also many cases where morphologically identical populations are treated as separate species because they occur in separate geographic regions. For example, it is common to treat seemingly identical forms living on separate islands or separate continents as separate species. A bird could be described, then, as a different species simply because it flew from one island to another!⁶,⁷

These different interpretations of the word species, what Locke would have called the "multiplicity of its significations," produce needless misapprehension in evolutionary discussion. For example, Bullock's Oriole is often treated as a species. That is, it is assigned the binomial Icterus bullockii. However, this bird interbreeds very extensively with the Baltimore Oriole, which is also often treated as a species (I. galbula). Anyone who accepted a biological definition of species and saw that Bullock's Oriole is treated as a species might suppose it had the traits specified by such a definition. Such is certainly not the case. These two birds produce huge numbers of natural hybrids that are partially fertile in both sexes.⁸ Conversely, there are many cases where populations treated as distinct races of the same species produce infertile or even absolutely sterile hybrids. For example, many populations treated as races of the house mouse (Mus musculus) fit this description.⁹

I can't find any date information on that page, so I don't know how old the info given there is, but there's a robust formulation of Mayr's definition (BSC) in use for quite some time. The examples given there don't impact the definition of species, they simply indicate that they were classified as separate either incorrectly or under a less robust classification system. The orioles cited there are sub-species in the same species. No problem at all. In the case of the mice, there are two possible explanations, neither of which poses a problem for a robust species concept, namely [1] they are sub-species in a ring or [2] they are separate species. Either case is dealt with nicely by the BSC. Again, this isn't a problem with the concept, it's a matter of how they've been classified.

Because in some cases categorization into species is done on such trivial differences yet there are examples of higher taxa interbreeding.

No. Classification is done via a variety of means, but erroneous classification isn't a problem with the concept, but the application. If they're interbreeding and producing fertile offspring, they aren't higher taxa, they're a single species.

Bonus weirdness – Different *genera* can hybridize. Right now in lab I have hybrids between a rat snake (genus Elaphe or Pantherophis, depending on which taxonomy you believe) and a king snake (genus Lampropeltis), and these hybrids are actually capable of reproducing with each other, and have produced up to F4 offspring with no noticeable reduction in fertility or increase. Based on comercial breeder’s stock, it seems like most North American members of subfamily Colubrinae can make fertile hybrids in captivity, and one recent paper reports such individuals from the wild. In the case of the most distant cross (the one I have), the lineages have been separate for almost 20 million years.

They're a single species under the BSC. The amount of time since separation is irrelevant. Speciation is based on time, it's based on interfertility.

Still stranger – there are apparently fertile hybrids of Alligator Gar and Longnose Gar, which have been separate for 180 million years according to molecular dating. Sadly, 12-foot fish don’t make good subjects for breeding studies.

Again, simply a case of incorrect classification. The time scale is irrelevant. It's a common error that time is a factor. Time is only a factor because generations require time, but you can't put any figure on how many generations are required for speciation, because even the number of generations is irrelevant. What matters is the degree of genetic divergence, and even that depends on where in the genome it occurs, meaning that there can actually be large differences in the genome, and even large resultant morphological difference, yet still gene flow can and does occur. If gene flow occurs, they are a single species.

Back to the drawing board.

The "reproductive isolation" can be genetic (non-fertility), geographic, or behavioral; there is no criteria that says (as is commonly believed) that if two populations can interbreed they are the same species. There is no criteria that says that two distinct species can't interbreed. Consider the example of wolves, coyotes and dogs: three distinct species that can interbreed. In fact, all species of the genus Canis can mate and produce fertile offspring (Wayne et al., 1997, re: A. P. Gray, Mammalian Hybrids). This is so common, that biologists actually use a different formulation of Mayr's definition: they say, "If two populations cannot interbreed, they are not the same species." That is a very different statement.