You can always try to reason with a Fundamentalist. You can always try to reason with a slathering Doberman too, for all the good it’ll do you. Myself, I prefer a good stout cudgel…..
Recently I had the pleasure of just such an encounter. While discussing the topic of evolution, the gent in question played what he thought was his trump card. If evolution is true, then how come humans aren’t evolving anymore?
He actually believed this to be a rational question.
Well, first off, when you consider the time-frame in question (and we’ll get back to the belief espoused by many Fundies and Intelligent Design folks that the universe is only between 6000 to 15,000 years old) the mutations that resulted in the current human race can be traced back, in theory, using both nuclear and mitochondrial DNA to a single female common ancestor in Africa around 200,000 years ago.
But, of course, the question remains: what made us “human?” What differentiated us from our primitive ancestors and why?
Research shows that humans (Homo sapiens) and chimpanzees (pan troglodytes) are 99.4 genetically compatible and that the species diverged roughly 5 to 7 million years ago. Humans have a total of 23 chromosome pairs, chimps have 24. Research suggests that two pairs of the 24-chromosome model fused to become the human 23, but this alone didn’t make us Homo the Sap.
Andrew G. Clark of Cornell University recently finished a very innovative study. Using a super-computer, he lined up a partial chimp DNA map of 18 million sequences along with the genome of a human and a mouse. (He would have used a rat, but couldn’t find a lawyer that would agree to give a sample…) The purpose was to determine which human genes were evolving at the greatest speed, the idea being that these genes might be the ones responsible for our “humanity.” Starting with 23,000 genes, he reduced this number to 7,645 that most differed from chimps and mice. The team then isolated the genes responsible for the development of sense of smell, digestion of protein (since chimps, although omnivorous, are predominantly vegetarians) development of long bones (such as the femur, tibia and fibula) hairiness and hearing.
The results seem to indicate that at one point in history, human sense of smell and amino-acid metabolism genetically diverged from those of the upper primates in order to better facilitate seeking out desirable and more varied food, and to digest the same with regard to assimilating proteins. This coincided with the archaeological evidence that early humans began eating meat around two million years ago. This new amino-acid metabolism may have resulted in triggering changes in other proteins. According to a study done by RIKEN Genomic Sciences Centre in Japan, certain proteins, including those that affect brain tissue, may have been genetically altered over time by our species’ switch to a more meat-related diet.
Then, the Howard Hughes Medical Institute isolated the ASPM gene whose mutations affect the size of the cerebral cortex. This protein is much more complex in humans than in other primates and might have been a decisive factor in evolving our “humanity.”
It has also been suggested that our genes governing the development of hearing might have been a direct contributor in the development of language by allowing more subtle sound differentiation. Chimps have lower hearing acumen the humans. In particular, one gene, alpha-tectorin, determines the makeup of the tectorial membrane in the inner ear.
There’s also endogenous retroviruses, whose existence drives Creationists apes__t, (or bananas, which George Carlin once pointed out is apes__t) who call them “intelligent common design” because they appear in both human and chimp genomes, are identical and indicate a common ancestor around five to seven million years ago. They code for viral proteins only used by viruses, but even if these little buggers had a function for the human organism, the odds against two species sharing such a thing is one in 10 to … well, followed by one hundred zeros.
But back to the original lint-headed question – are humans still evolving today? Well, yes, of course they are, but very subtly. Take, for example, Yersinia pestis, a bacterium living on rats that caused the Bubonic or Black Plague which affects the human immune system making the victim more susceptible to opportunistic diseases such as typhus, TB, smallpox, etc, plus its own nasty symptoms.
Diseases like the Black Plague and HIV gain access to the human body by creeping past the cell membrane by creating a chemokine receptor. The design for these receptors are found in our genes. For people who had a high resistance to the Plague or HIV, the gene involved in the production of chemokine receptors is defective. If two parents, both with the defective gene produce a pair, this results in no receptors at all and HIV is shut out by the body’s natural defenses. This genetic mutation, known as Delta 32, is found in its highest frequencies in English, Scandinavian and Germanic Peoples, most likely the same gene that gave their ancestors resistance to the Black Death.
One of the things that inhibits our ability to actually see evolution of the human species happening is our longer life spans and a population of over 6 billion. However, that doesn’t mean it’s not occurring – it is, but at a rate measured in centuries.
Now – if only a mutation could occur that would wipe out stupidity…