caravelair

i am engaged in a debate with a creationist who insists that we are "de-evolving" (whatever that's supposed to mean) rather than evolving. he insists that our genetic code is getting worse over time. i realize a few errors in his idea, but since i have a quite limited knowledge of genetics, i would appreciate some help from some of the geneticists and biologists on this board, so that i can put this idea of his to rest for good. his latest post goes as follows:

Calzaer

Once we started manipulating our environment, as opposed to our environment manipulating us, evolution got kinda sketchy. We keep genes in the pool that should have died out by now; congenital diseases and poor eyesight, for example. That's an example of human compassion overcoming "nature red in tooth and claw", not a condemnation of the theory of evolution.

Monkeybot

Well the concept of "de-evolving" makes no sense. I think your fundy friend is making the assumption that evolution is progressing towards some kind of goal, which it is not. There is no goal of evolution; it's a theory which simply describes how populations change. Evolution doesn't care whether populations "improve" or go extinct.

Wounded King

In cancer it could be argued that we do see natural selection. The cancerous cells are simply the more succesfull type. They reproduce and invade other tissue types and consequently the cancerous genotype is more successful simply because its growth and motility is no longer restrained. Obviously this is heritable in terms of other cells derived from the neoplasia being genetically similar. If tumourous cells are injected into a new host they can go on to form further growths. If cancers could survive without a host entirely, other than in cell culture, then maybe they would become a new species.

But any argument about degradation of somatic cell genetic information has nothing to do with evolution of the species which would rely on mutations in the germ line cells.

What is best for our health in terms of cancer etc. is not neccessarily what is chosen by natural selection. Most cancers occur well after reproductive age has been reached after all, so there isnt any impetus for natural selection to develop mechanisms to combat it through old age.

As for hereditery diseases, many of them come from mutations which, for one reason or another, occur relatively frequently, which cannot be compensated for. In some cases, sickle cell anemia for example, there is some environmental factor which means that there is some advantage from heterozygotic posession of the defect which allows it to be mantained in the population. Again it also depends when the disease presents, if it is subsequent to reproductive age then natural selection couldnt care less about it, for instance developing parkinsons in your 30s isnt going to prevent you having children, especially if you have them in your 20s.

Your correspondent seems to feel that evolution should be constantly working to make his life better for him, sadly this is not how it works.

As to there being more detrimental than beneficial mutations I feel there is something of a problem here. We are aware of hundreds of detrimental mutations because they cause diseases and medical science puts a lot of effort into developing cures or finding a better understanding of these diseases. I fear that were you to write a grant proposing to look for beneficial mutations in anything higher than a bacteria you would get an awful lot of people shouting you down for planning some sort of eugenic society run by scientists. Even in the case of deleterious mutations it is mostly only the very severe ones we know about, there are undoubtedly thousands of mutations, both deleterious and beneficial, which we are simply not able to discern, our inability to do so does not stop natural selection acting on them however.

caravelair

he's not really using the term "de-evolution" in the sense that you are thinking. he's just trying to find some "science" behind his idea that adam and eve lived for 900 years or so, and we have been accumulating genetic defects since then causing our life expectancy to drop, etc. of course he could never possibly present any evidence of this occuring, but i would also like to make sure he is aware that it is theoretically impossible to eliminate any hope that he might find some evidence in the future. while i have explained to him that natural selection only passes on positive mutations, he will refer to examples such as sickle cell anemia genes being beneficial in an environment with malaria. and asserting that such things accumulate. i know enough to explain to him some of faults of his idea, but i was hoping for some stronger information that would allow me to irradicate this idea from his mind once and for all. or at least come as close as possible.

thanks for the help, everyone.

theyeti

All cell lines wear out over time. Most cells are good for about 50 divisions before they senese. (That might not sound like a lot, but it's enough to give you 2^50 cells -- or about one quadrillion -- starting from just one.) The exceptions are immortalized cells which never die. They just keep reproducing forever, but you don't want those: they're cancerous. For unicellular organisms, this is how they get along. They just reproduce faster than they accumulate deleterious mutations, and selection weeds out the bad DNA. A unicellular organism is really just like a cancer cell that's free living. In fact, you can take a cell line from any old eukaryote and culture it forever if it becomes immortalized (i.e. cancerous). One example is the HeLa cell, named for Henrietta Lacks, the woman whose tumor they were cultured from. Though they were first cultured back in the 1950s, the cells are still doing fine and in fact are contaminating other cell cultures and basically making a nuisance of themselves. And by now the total mass of this woman's tumor cells is probably enough to build thousands of people. Try asking your creationist friend why these cell lines can live forever. Or for that matter, how does he account for the continued presence of any unicellular organism?

As for us tumor-free multicellulars, we have to reproduce ourselves before all of our cell lines have become too old. The cells get "recharged" somehow during gametogenesis. While I haven't kept up with the recent research, IIRC the repair of double stranded DNA breaks during recombination is a major way to fix damage that somatic cells cannot fix. The repair of telomeres via telomerase is another way. And there are other ways that we don't know of yet; when we do, we'll basically have a complete understanding of the aging process. But at any rate, just like the unicellulars, we humans reproduce ourselves faster than deleterious mutations accumulate in our DNA too. We can do because we have specialized cell lines that don't have to divide so much that they create the whole organism, and because we have sexual recombination and a relatively slow mutation rate.

theyeti

Grumpy

It's like deceleration. Physicists will say there's no such thing, there's only acceleration opposite from the direction of movement. "Deceleration" is a layman's term.

Butters

If he is a YEC, ask about the flood. If all the animals alive today "evolved" from a few kinds, even if it is only "microevolution", where did the information come from. If lions, tigers, cheetahs, house cats, Etc. came from two "cats" so that all animals fit on the ark, how could all these cats develope?