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Study Detects Recent Instance of Human Evolution
The New York Times is running a Sunday article regarding new evidence about 'recent' human evolution. A research team at the University of Maryland has done some work looking at the rise of lactose tolerance in the human populations of Africa. From the article: "The principal mutation, found among Nilo-Saharan-speaking ethnic groups of Kenya and Tanzania, arose 2,700 to 6,800 years ago, according to genetic estimates, Dr. Tishkoff's group is to report in the journal Nature Genetics on Monday. This fits well with archaeological evidence suggesting that pastoral peoples from the north reached northern Kenya about 4,500 years ago and southern Kenya and Tanzania 3,300 years ago ... Genetic evidence shows that the mutations conferred an enormous selective advantage on their owners, enabling them to leave almost 10 times as many descendants as people without them. The mutations have created 'one of the strongest genetic signatures of natural selection yet reported in humans,' the researchers write. "
I realize that this is popular press and all, but why is mutation always mentioned, but crossover, never so?
Generally speaking, mutation is almost always fatal, crossover is almost never so. Crossover keeps you "in the genome", where mutation is just as likely to kick you out of it. My own theory is that mutation is the driver behind speciation, while crossover is the driver behind evolution.
I've run lots of GAs with mutation turned off, letting crossover do all the work. Crossover, not mutation, is what lets a population do that slow walk/hillclimb, over time, through the genetic landscape.
No folly is more costly than the folly of intolerant idealism. - Winston Churchill
It's not actually that simple. For example, the increase in height in Westerners isn't micro-evolution it's simply diet. When man went from hunter-gather (the state to which we evolved), to an agrarian lifestyle, the quality of diet went down, it hit rock bottom in Europe in the middle ages where teh majority of the population were quite severly malnourished and therefore short. The heights we are currently reaching (pun intended) are basically those of our hunter-gatherer forefathers, because as a population the quality of our diet over the last 50 years has improved so much. Of course we're probably heading down the path of too much now...
So my point is, that it's not easy to define or prove 'micro-evolution'. Just to clarify, I am a biologist by trade and am quite comfortable with the punctuated-equilibrium model of evolution, I'm certainly not arguing that evolution doesn't happen, just that we have to be careful with our conclusions.
Si hoc legere scis nimium eruditionis habes.
Mmmm... I think saying "I really don't think" is quite honest of you, although it is already painfully obvious to most of us here.
Humans originally didn't have the enzymes to digest cow lactose; why should they? It serves no purpose in a hunter-gatherers genome.
Most infants can digest lactose well enough to get by as they are expressing genes at that age to aid in the digestion of human milk, but by age 5 cow milk normally makes a lactose intolerent person puke mucus.
Occasionally through mutation some did have the right enzymes to digest cow lactose through adulthood, but as humans did not keep cows those people had no advantage over other people without the mutation, so the mutation was lost as it had no benefit.
When humans started to keep cows they had access to a new food source, milk.
This would have been used to feed infants to replace or suppliment the mother's milk, probably as part of the weaning process.
As those infants grew older those with tolerence to lactose had access to a renewable food resource denied to those who were intolerent to lactose. Those lactose intolerent infants whose parents kept feeding them milk would have been sickly and malnourished.
There would be such a big ebenfit to lactose tolerence that somethng called 'runaway evolution' took place. It's a bit like how mudskippers evolved; if ten fish of a species in a river survive a drought survive because of x charecteristics only they (in that species) have, after that drought all members of that species have x characteristic.
Similarly with human lactose tolerance the stronger, better fed, healthier members of the population with lactose tolerence would have had way more offspring then those who didn't have the genes for it, and those offsrping would fare better.
If 5% increase in genetic transfer through natural selection can make a new characteristic spread throughout a population in less than 200 generations, think how more quickly one with a much higher advantage might spread.
Guns are part of an extended phenotype, and are NOT subject to genetic transmission. Idiot.
I read the article, I'm not the Breast Surgery Chief but I do have a fairly solid background in biology. The thing that made my bullshit meter go into the red is when he tried to discredit pasteurization. Also, he uses very weak arguments and then doesn't back them up. You can't just say milk has bacteria, bacteria makes people sick, therefore milk is bad ... it's simply too broad a brush to use in biological terms. If you want to talk about scary stuff, look at all the recent fecal coliform contaminated vegetables in this county. If this author took a stance on that subject, it would read like this: fertilizer and reclaimed water used to irrigate vegetable fields contain fecal coliforms, fecal coliforms make people sick, therefore vegetables are bad. Disconnected facts do not an argument make.
Good people do not need laws to tell them to act responsibly, while bad people will find a way around the laws-Plato
I just wanted to add a note on the milk digression, I suppose. There are huge nutritional differences between pasteurized and raw milk, in terms of health benefits to humans. The live enzymes present in raw milk (phosphatase for cascium absorbtion, lipase for fat digestion, lactase/-ose, galactase/-ose, catalase, diastase, peroxidase, etc) are destroyed to a large extent by the pasteurization process. In raw milk, all 22 amino acids are present as well, whereas in pasteurized milk, the polypeptides lysine and tyrosine are changed by the heating process such that they are not as easily metabolized (meaning your body can't use the proteins as readily or as easily). Vitamins A, F, E, and D are lost to a large degree by the heating process as well, as is Vitamin C (though to a lesser degree). B6 and B12 are pretty much destroyed all together. Also, raw milk is seriously tasty. If you ever to a taste comparison, there's really no contest. It's a full, earthy flavor, whereas the flavors of pasteurized milk and milk products are shallow and less complex. Obviously, drinking raw milk has its risks. It's important to know where your raw milk is coming from and the process by which it's being produced. If the cows are fed what cows are supposed to be fed (grass, pasture plants, etc) and if the conditions on the farm are clean and natural (no anti-biotics, no hormones, no cows being fed other cows, no over-crowding), there shouldn't be a problem with pathogenic bacteria in the raw milk and it should be safe for human consumption. The beneficial bacteria, as the dominant culture, will prevent the growth of harmful bacteria (whereas in pasteurized milk, a sterile medium, there is no active culture of good bacteria to prevent bad bacteria growth). Going to the farm yourself is the best bet, although there are many states in which it's illegal for farms to sell raw milk due to the risks involved with sub-par milk production (factory farms, etc) and so raw milk purchases, even at all-natural organic farms, have to be made rather on the down low. It's good, though, for people to be involved more in their food, to know where it's coming from, to take an active role in their health and diet through awareness of the production process and its results. Also, a last thought: I don't think that relying on milk as a sole source of calcium would be good, but then, relying on any one thing for nutrition is probably not wise. Moderation and diversity are most likely the best routes to take. Go team Human.