SR-5 (Short Read #5)
Excerpt* from Discover Magazine article:
They Don't Make Homo Sapiens Like They Used To
by Kathleen McAuliffe
Back a few years ago, I had the pleasure of working with an intelligent young man named A. Catlin in our lab during his undergraduate days at KSU. His mother is a teacher and the Mrs. CoachHays is a teacher (in fact AC was in the very first class Mrs. CoachHays ever taught and he once turned in a report on Richard M. Nixon that brings tears to the eyes, but that is another story for another day) so we occasionally talked of education issues. At that time ADHD was big time issue in the schools, kids were being branded and Ritalin was being dosed out like candy hearts at St. Valentines Day. One day, we looked at an "official" list of symptoms of ADHD and discerned that each of us competently fulfilled the requirements of 90% of the symptoms on the list. AD said once his dad, the hon. M. Catlin, financier, took an ADHD screening test his mother had brought home from school and both failed it miserably. I have often wondered how different my life and the life of many competent, intelligent, creative people may have been had we been pigeon-holed into a program to deal with "afflictions" we never even realized we had.
I picked this excerpt from the excellent article on the continual process of adaptation of the human species to show that even a "affliction" such as ADHD appears to have a useful function. Without the DRD4 mutation associated with ADHD forcing us human folk to roam, explore and push the acceptable limits, we would all still be sitting in a very crowded river valley somewhere in the African Savannah.
SIDE NOTE: I think one of the major arguments arising is science is going to be between the groups who think human genetic evolution stopped 50,000 years ago and the groups who believe that human genetic evolution is occurring at an increasingly rapid rate.
*EVOLUTION AND THE BRAIN
Perhaps the most incendiary aspect of the fast-evolution research is evidence that the brain may be evolving just as quickly as the rest of the body. Some genes that appear to have been recently selected, Moyzis and his collaborators suggest, influence the function and development of the brain. Other fast-changing genes—roughly 100—are associated with neurotransmitters, including serotonin (a mood regulator), glutamate (involved in general arousal), and dopamine (which regulates attention). According to estimates, fully 40 percent of these neurotransmitter genes seem to have been selected in the past 50,000 years, with the majority emerging in just the past 10,000 years.
Addressing the hot-potato question—What might these changes signify?—Moyzis and Wang theorize that natural selection probably favored different abilities and dispositions as modern groups adapted to the increasingly complex social order ushered in by the first human settlements.
When people in hunter-gatherer communities have a conflict, Moyzis reports, usually one of them will just walk away. “There is a great deal of fluidity in these societies,” he says, “so it’s easy to join another group.” But with the establishment of the first farming communities, we put down roots figuratively as well as literally. “You can’t just walk away,” Moyzis notes, a fact that would have created selection pressure to revise the mechanisms regulating aggression, such as the glutamate pathways involved in arousal. “When you domesticate animals, you tend to change genes in that system,” he says.
For decades theories about human evolution proliferated in the absence of hard evidence, but now human genetic data banks are large enough to put assumptions to the test.
The rise of settlements also promoted the breakdown of labor into specialized jobs. That, coupled with food surpluses from farming, led to systems of trade and the need to track the flow of resources, which in turn could have selected for individuals with specific cognitive strengths. “Mathematical ability is very important when it comes to keeping track of crops and bartering,” Wang says. “Certainly your working memory has to be better. You have to remember who owes you what.” The researchers point to China’s Mandarin system, a method of screening individuals for positions as tax collectors and other government administrators. For nearly 2,000 years, starting in A.D. 141, the sons of a broad cross section of Chinese society, including peasants and tradesmen, took the equivalent of standardized tests. “Those who did well on them would get a good job in the civil service and oftentimes had multiple wives, while the other sons remained in a rice field,” Moyzis says. “Probably for thousands of years in some cultures, certain kinds of intellectual ability may have been tied to reproductive success.”
Harpending and Cochran had previously—and controversially—marshaled similar evidence to explain why Ashkenazi Jews (those of northern European descent) are overrepresented among world chess masters, Nobel laureates, and those who score above 140 on IQ tests. In a 2005 article in the Journal of Biosocial Science, the scientists attributed Ashkenazis’ intellectual distinction to a religious and cultural environment that blocked them from working as farm laborers in central and northern Europe for almost a millennium, starting around A.D. 800. As a result, these Jews took jobs as moneylenders and financial administrators of estates. To make a profit, Harpending says, “they had to be good at evaluating properties and market risks, all the while dodging persecution.” Those who prospered in these mentally demanding and hostile environments, the researchers posit, would have left behind the most offspring. Critics note that the association between wealth and intelligence in this interpretation is circumstantial, however.
Stronger evidence that natural selection has continued to shape the brain in recent epochs comes from studies of DRD4, a mutation in a neurotransmitter receptor that Moyzis, Wang, and many others have linked to attention-deficit/hyperactivity disorder (ADHD). Children diagnosed with ADHD are twice as likely to carry the variant gene as those without the diagnosis. DRD4 makes a receptor in the brain less effective in bonding to dopamine, which might explain why Ritalin, which increases the amount of dopamine in the space between neurons, is often helpful in treating the problem.
Sequencing studies suggest that the DRD4 mutation arose 50,000 years ago, just as humans were spreading out of Africa. Its prevalence tends to increase the farther a population is from Africa, leading some investigators to dub it “the migratory gene.” At least one allele (or copy of the gene) is carried by 80 percent of some South American populations. In contrast, the allele is present in 40 percent of indigenous populations living farther north in the Americas and in just 20 percent of Europeans and Africans. Children with the mutation tend to be more restless than other youngsters and to score higher on tests of novelty-seeking and risk-taking, all traits that might have pushed those with the variant to explore new frontiers.
In the context of a modern classroom, it may be hard to understand why kids who appear distractible and disruptive might have a survival advantage. But research shows people with DRD4 do not differ in intelligence from national norms; if anything, they may on average be smarter. Moreover, behavior that may seem like a drawback today may not have been so in ancient environments. When broaching foreign terrain filled with unknown predators, “having the trait of focusing on multiple directions might have been a good thing,” Wang says. “People focused in one direction might get eaten.”
Humans in far-flungdomains encountered starkly different selective forces, adjusting to novel foods, predators, climates, and terrains.
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