The Economist reports studies of human genomes around the world:
The team identified several hundred genes that had undergone recent selection in at least one of the populations being studied. Some were not surprising. Genes involved in the generation of sex cells, and in fertilisation, are known from other work to have strong selective pressures on them, and those pressures clearly continue in modern humans. Nor was it much of a shock to discover selection, in Europeans, for changes in four skin-pigmentation genes known to be involved in reducing melanin content.
Perhaps the most intriguing results were those connected with food metabolism. The gene for alcohol dehydrogenase is undergoing selection in Asia, as is that for processing sucrose (table sugar). Meanwhile, the genes for processing two other sorts of sugar, lactose (found in milk) and mannose (found in some fruit) are changing in Europeans and Yoruba respectively. Fatty-acid metabolism, too, is changing in all three populations. And Europeans are having the toxin-disposal systems in their livers modified.
Some brain genes are also changing, including two that control the size of brains, and two involved in susceptibility to Alzheimers disease. And three genes that control bone growth have been modified in Europeans and East Asians, while the Yoruba have seen changes in genes that control hair growth.
Well, in this case I yield that some populations, especially those in Asia whose medical resources are inferior to western countries, may be experiencing some adaption to changing foods.
Without seeing the stats (i'm not subscribing to these journals for the purpose of one thread) i'll have to base my argument on this rather poorly written synopsis.
Ok number one, selection involving germ cells and fertilisation.
Helpfully this synopsis fails to mention where there findings originate, the process of selection on this basis is obvious though - those with better fertilisation rates pass on more of there genes and so their genes are selected for. This happens in all species.
But uh-oh, what have we got in the west now? Yep, you guessed it in-vitro fertilisation, and very advanced it is now too. This bypasses ALL selection pressures involved in fertilisation for those who can afford the procedure - those in the rich western countries. That's one debunked, next...
Skin pigmentation in caucasoids.
This has been going on for tens of thousands of years, if not longer. I don't know where they've found recent studies showing further reduction in melanin, but it certainly wasn't in the west. Why?
Vitamin suppliments. The only reason for melanin reduction is to gain more vitamin D synthesis from sunlight. In the west if a person is deficient in vitamin D they show symptoms, then they go to their GP and s/he prescibes them vitamin suppliments. Selective disadvantage removed...
Alcohol dehydrogenase increasing in Asian populations.
I can buy that, people become alcoholic in China they get cirrhosis and die. Are most Asian countries medically up to the standard of western states? Nope. This point is moot in reference to my original suggestion.
However, i do accept that some selection may also be occuring in the west as well, people die young from alcohol related deaths and they fail to breed. They survive their addiction because of better degeneration of alcohol, they get to breed. The problem then arises with liver transplants which give the individual a second chance to pass on any addictive habit forming genes they possess onto their children
Lactose digestion changes in carcasoids.
Well, much like the skin pigmentation example this has been going on for many thousands of years. What are the changes they are talking about though? They don't say these changes are beneficial. I suggest the changes they are talking about are more likely an increase in lactose intolerance within the population. Why? Because lactose intolerance is easily diagnosed and so dairy produce can be avoided. These people pass on their intolerance and so the genes spread. It is reversing the natural trend for improved lactose digestion in our ancestors. If anything, this is devolution.
They suggest that brain size is changing. Well, maybe in third world countries where smarter people survive and stupid people die. I don't know about you, but i know many many stupid people that are breeding here in the west.
Alzheimers does not usually affect people until they are past middle age, most have had children by then. I can't see how these genes can therefore be affected by selection pressure and would suggest an alternative reason for their findings, if that is their findings are even valid.
As for the Yoruba, i don't know enough to comment. However last time i checked west African countries haven't been on the cutting edge of medical advancement. Adaption in these people i can accept. But i'm talking about evolution in
western societies...
In closing, i originally stated that i believe evolution of the human population in western societies has plateaued. We have removed almost all selection pressure that would otherwise weed out the weaknesses in our population.
We have asthma, cystic fibrosis, epilepsy, hemophilia, muscular dystrophy, huntingtons disease as well as cancers of the breasts and lower digestive system - all of which are hereditary (an increased chance of development in the case of the cancers). These are
increasing in western populations, and in other populations influenced by western medicine.
We have stopped evolving because we have the ability to help our weak and sick, to let them live normal lives and pass on their genes.
If we are being entirely technical, we
could say we are evolving as there have been changes in gene frequency. However, in nature these changes which lead to micro and macroevolution are always positive changes. In western cases they are negative, it is the opposite to natural selective pressure driven evolution and thus, in my humble opinion cannot truly be classified as being the same thing.
In reference to my discussion with Jeff. The reason a child we selected at random would probably die earlier if sent back in time 2000 years, is a combination of lack of immunity to wiped out disease (smallpox for example) and the fact that they are reasonably likely to have a debilitating disease that without our modern medicine would kill them.