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Planet Earth

Cystic Fibrosis? Blame Eve

The LoomBy Carl ZimmerAugust 7, 2006 7:33 PM


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Last night, as my family settled into a three-hour drive home, I began scanning the AM radio dial. The tuner stopped at on a well-produced segment in which the announcer was talking about recent evolution of pigmentation genes and lactose-digestion genes in humans. This is a surprise, I thought, and I settled in for a listen. It took about twenty seconds for me to realize that this was the work of creationists. I spent the next fifteen minutes listening to the piece with jaw aslack, making sure I didn't get so distracted I missed my exit. There is something so absorbing about the elaborate rhetorical gymnastics that creationists engage in order to square their views with new scientific evidence. This morning I did a little research online and discovered that what I had heard was part of a weekly radio program from the Institute for Creation Research. It claims that all of the new research on recent evolution in humans does not actually serve as evidence of evolution, but rather of man's recent creation and fall. They dismiss the examples of recent evolution in various ways. They are just minor changes, for starters, not the sort that produce "fish-to-philosopher" evolution, as the announcer put it. They just tweak the human form. Or these mutations consist of losses, rather than gains, through mutation. Humans have lost olfactory receptor genes, for example. The radio show then explains the real origin of all these patterns in our genome. The Institute for Creation Research was founded to promote Young Earth Creationism--the claim that the Earth is only a few thousand years old. The announcer explained that the minor variations in the human genome originated at the time of the flood, or at the creation of man at the earliest. Mankind was created with a perfect genome, we are told, and once we turned away from God through sin, our genome has been degrading ever since. All mutations that have accumulated since the fall of man have led to the loss of genes and to disease. I have to say that the "Genomic Degradation as Original Sin" line was new to me. But in order to make this case, the radio show engages in the three classic creationist errors. Error #1: Get the science wrong. In order to portray recent mutations as nothing but loss and suffering, ICR must distort the facts. Take their discussion of mutations that provide protection for malaria but can also cause sickle-cell anemia. An ICR "scientist" tells us that all this mutation does let people die of sickle-cell anemia at age 15 instead of dying of malaria at age 10. Earth to ICR: if what you say is true, then why do so many people have these mutations? Why didn't they all die before they could pass that awful gene down to children? Because people only get sickle-cell anemia when they inherit two copies of this gene. One copy gives protection to malaria. On balance, natural selection thus favors the gene in regions with high rates of malaria. The radio piece also makes a big deal about the digestion of lactose, a sugar in milk. It describes some populations as producing lactase, the enzyme for digesting lactose, and others as not producing it. Thus, this is just another case of a mutation destroying "genetic information" rather than creating it. Second transmission from Earth to ICR: if what you say is true, then babies in those populations that cannot digest lactose should all die. After all, they cannot digest the lactose in the milk they get from their mothers. Here's the real story: all mammals produce lactase as babies, in order to break down lactose in milk. Then, after weaning, the mammal's cells stop reading the lactase gene. Since adult mammals don't drink milk, making an enzyme to break down lactose is a waste of energy. The timing of this switch is under genetic control, and mutations can delay it until later in life. In human populations where cattle-herding became important, mutations that allowed humans to continue making lactase as adults were favored by natural selection. So nothing was lost. In fact, dare I say it, these human populations gained an adaptation that their ancestors lacked. Error #2: Skip over inconvenient facts. The ICR molecular biologists and science professor from Liberty University throw out lots of details, which may give the impression that they're telling you everything there is to know about the evidence of recent evolution. But they skip over major things that would knock out the basis for their claims. For example, they claim that all the genetic changes that scientists have identified have nothing to do with the major changes that would have arisen on the way from ape-like ancestors to humans--such as an increase in cranial capacity. They conveniently skip over the genes that have been identified as having experienced natural selection in our ancestors that play a role in language, brain size, and brain development. Error #3: Contradict yourself. You can only conclude from this radio piece that the folks at ICR accept the evidence that humans have recently acquired mutations. But in many cases, scientists can only determine recent changes in humans by comparing our genomes to our relatives--chimpanzees, for example, and mice. By studying their genomes, scientists discover what our ancestral genome was like, and can then pinpoint the changes that arose in our genome after our ancestors split off from other species. If the ICR accepts these examples of recent human genetic change, then they must accept our common ancestry with chimpanzees and mice. I am not a theologian, and so I won't try to dive too deeply into the religious implications of thinking of our genomes as the result of original sin. But I do wonder how one makes that sort of idea work. The ICR radio show claims we lost our olfactory receptor genes since the flood. We have 388 working olfactory receptor genes and 414 broken ones (called pseudogenes). Mice, on the other hand, have 1037 working receptor genes and 354 psuedogenes. Many of their working genes have counterparts among our pseudogenes, which is some of the main evidence that our ancestors lost many genes involved in smell. So does that mean that mice enjoy an Edenic perfection that we have lost? Anyway, let you own mind roam free: here's the show in mp3 and real audio. And if you are hungry for more, here's the radio show archive. It's a fact-checker's paradise.

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