How Natural Selection is Cumulative

Posted on November 8, 2008 by Michael

Tale Of Two Snails Reveals Secrets About The Biochemistry Of Evolution

In the new study, Emilio Rolán-Alvarez and colleagues note that scientists long have known that animals of the same species can have different physical characteristics enabling them to survive in different habitats. One famous example is the different beak sizes and shapes that evolved in Darwin’s finches, enabling the birds to live on different foods in different habitats on the Galapagos Islands. Until now, however, scientists knew little about the invisible biochemical changes behind such adaptations.

To help fill those gaps, the scientists studied two populations of marine snails that live only a few feet apart on the Spanish coast. One group lives on the lower shore, typically submerged in water and protected from large changes in temperature. The other group lives on the upper shore exposed to daily changes in temperature, humidity and other environmental conditions. Tests with mass spectrometry showed major differences in about 12 percent of the proteins in the snail, a subset of proteins that apparently enables the snails to survive in different environmental conditions.

This is a wonderful example of the how natural selection works in a cumulative way. Rather than the misconception that entire organs and bodily systems come into existence in one fell swoop, this study of snails offers a taste of reality.

Notice that these snails have the same set of proteins. However, between the two groups, there are differences within the proteins. Essentially, the proteins are expressed differently. At least part of the reason has to do with differing levels of ATP, or energy. That is, these proteins are regulated slightly differently, but differently enough to allow for this species of snail to live in two distinct environments. This can be important in explaining the cumulative effects of natural selection – this is still one species of snail, but they have minute differences in just 21 proteins which allow for slightly different living conditions. If the snails continue to diverge and actually fully speciate (they are in a state of sympatric incomplete speciation now) – i.e., they cannot or simply do not produce fertile offspring – then it is highly likely that such an event would be contigent upon this first deviation in protein regulation.

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Great New Tiktaalik Research

Posted on October 16, 2008 by Michael

Details of Evolutionary Transition From Fish to Land Animals Revealed

So the jist of this new research is that Tiktaalik roseae has been vetted a bit better. Researchers viewed several Tiktaalik fossils and discovered some interesting new information on its internal anatomy. Of specific interest is the hyomandibula. Its function has changed significantly from its early arrival in fish to its current use in mammals. As it stands, this bone functions as part of the ear for mammals. It also functions as part of cranial motions for fish, namely it is very important to gill respiration. In Tiktaalik, it had a transitional function. That isn’t to say it acted as a sort of ear-gill. It didn’t. It had a function that resulted in better cranial movement, inherently giving it less importance toward gill respiration.

What’s really important here is to realize that this is the exact same bone in mammals as it is in fish. If Tiktaalik lies somewhere between fish and most land animals, we should see quite a few features lying in between. That’s precisely what we see. What’s further, this should help to demonstrate that when scientists speak of transitional features, they do not mean hybrid phenotypes like ear-gills or the silly crocoduck

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