Once again, I thought I was going to learn something devastating from an evolutionist–something that would really rock the creationist boat. A few years ago I listened to the audio version of Neil Shubin’s book Your Inner Fish, and since then I’ve watched for more evidence of evolution in homology. So when PZ pointed to this article “proving” that humans inherited certain genes from yeast, I was intrigued:
Edward M. Marcotte is looking for drugs that can kill tumors by stopping blood vessel growth, and he and his colleagues at the University of Texas at Austin recently found some good targets — five human genes that are essential for that growth. Now they’re hunting for drugs that can stop those genes from working. Strangely, though, Dr. Marcotte did not discover the new genes in the human genome, nor in lab mice or even fruit flies. He and his colleagues found the genes in yeast. . . .
The scientists took advantage of a peculiar feature of our evolutionary history. In our distant, amoeba-like ancestors, clusters of genes were already forming to work together on building cell walls and on other very basic tasks essential to life. Many of those genes still work together in those same clusters, over a billion years later, but on different tasks in different organisms.
The NYT reporter carpet-bombs the reader with references to evolution, just to make clear what the underlying ideology is; he even mentions Darwin three times. I thought, “Gee, this is really convincing. What else except common descent could explain the presence of the same genes in such different species?”
Well, there is another possibility: horizontal gene transfer. In an article that makes only a token mention of evolution, we read this:
Aphids, those sap-sucking foes of gardeners, come in a variety of colours. We usually think of them as green, but pea aphids sometimes wear a fetching red ensemble. . . .
But it’s the source of the pea aphid’s ability that’s truly remarkable – it stole the skill from fungi. By integrating fungal genes into its own genomes, it gained a superpower that almost all other animals lack.
These sorts of “horizontal gene transfers” go on all the time in bacteria, but they’re supposedly a rarity among more complex creatures like animals and plants. And yet, scientists have recently documented several examples of such transfers. Rotifers smuggle genes from fungi, bacteria and plants. “Space Invader” genes have jumped across animals as diverse as lizards and bushbabies. One bacterium, Wolbachia, has even inserted its entire genome into that of a fruit fly. And parasites can transfer their genes to humans.
Now then, I don’t know why the NYT reporter completely ignored horizontal gene transfer and instead wanted to tell a story about conserving yeast genes for a billion years, whereas the Discover Magazine reporter mentioned evolution only as an afterthought. Here is one possible explanation:
The pea aphid’s story tells us that genetic swaps between complex species like fungi and animals are possible, although probably still rare. Before now, scientists did actually try to search the pea aphid genome before for genes transferred from other species. But they only looked for genes of bacterial origin; no one considered that the donors might be fungi, so the carotenoid-making genes were never found.
The implication is that the scientists’ bias previously prevented them from considering what now seems to be the most likely hypothesis. Yet, guys like PZ claim that the overall story of evolution is a known fact, and the mechanisms are trivial.
I say it is best if scientists confine their hypotheses to processes that they can observe and manipulate, rather than making up stories about the distant past as part of a war against religion.