Are We Evolving?

In the future, will the human race evolve giant, watermelon-sized brains, the huge crania barely supported by pasty-white and frail bodies? Or, like the tyrant overlords in Madeline L'Engel's A Wrinkle in Time, might we progress to the status of brains floating in nutrient solution? Alternatively, might we evolve a caste system, with future humans partitioned like termites into worker, soldier, and thinking classes? Or perhaps we will regress both physically and mentally, as Aldous Huxley's Ape and Essence, degenerating into a senseless species of cripples, gibbering like idiots.

Perhaps our organic evolution is irrelevant at this late date, since the eventual replacement of organic Homo sapiens by intelligent thinking machines made in our image, is just around the corner. As more and more people opt to upload their thoughts and memories into cybernetic immortality, will our species leave this planet behind for an existence in some cybernetic realm?

The literature of science fiction is rich with fantastic speculation about our evolutionary destiny. In Nat Schacher's "Past Present and Future", a hundred thousand years of evolution create a future human race composed of worker, technician, and oligarch castes, all teeming like ants within a subterranean hive. H. G. Wells' extrapolations of human evolution are legendary, with a nocturnal, carnivorous human species preying upon their dim witted and gentle sister species. This vision of future humanity in The Time Machine was presaged in Wells' When the Sleeper Wakes, where he shows the huge hive cities and the class distinctions that might ultimately lead our social classes to follow separate evolutionary paths. In A. E. Von Vogt's Slan, the superior species resulted from some sort of major mutation, with multiple types of mutants living as persecuted minorities. Olaf Stapledon's visionary The First and the Last Men postulates not just a single evolutionary descendent of Homo sapiens, but a series of 16 future humans. These include seal men, winged men, a race of malevolent intelligent monkeys, and the benevolent and doomed last men of Neptune, possessed with vast intellect and forethought.

And yet, as humans, we seem to have insulated ourselves from nature "red in tooth and claw". From the viewpoint of an easy chair, it is not clear that some traits confer a reproductive advantage and others do not. Are we evolving?

The answer is yes. All species evolve, though the rate of evolutionary change can vary tremendously among species, and for any given species, can vary from one span of time to the next. In the last fifty years, we have seen astonishingly rapid evolution of pesticide resistance in insects and antibiotic resistance in pathogens. Artificial selection via domestication has brought monstrous new creatures into existence from sensible and innocuous wild ancestors. Maize, for instance, evolved from a weedy Mexican upland grass resembling the weed teosite, into the tall, large-seeded and distinctive plant that occupies so much of the world today. Tomatoes, bananas, and other plants, have underwent similar transformations. Some species seem not to evolve at all for vast spans of time. The horseshoe crab, Limulus sp., is very difficult to distinguish from reconstructions of fossil ancestors that crawled the seas 200 million years ago, and the giant sequoia tree Sequoiadendron giganteum could be transplanted to a Cretaceous period forest and not seem out of place. These species have evolved, nonetheless, in thousands of subtle aspects associated with tracking the ecological niche that allows them to survive as they do. For them, the game is stabilizing selection, rather than directional selection…natural selection weeds out the individuals that depart too much from the configuration that has worked so well for these millions of years.

What about humans? Will we continue the rapid evolutionary change of the last 5 million years? Or sink into a pattern of evolutionary stasis like horseshoe crabs?

Our species yields tantalizing clues for speculation. It is a rule that large, widely-distributed species living in large populations mixed by the movement of individuals, frequently remain unchanged for vast amounts of time. It is the small, fractured populations that show rapid evolution, generally, and have the most opportunities to give rise to new species as well. Interestingly, however, a large number of widely-distributed species have exhibited dramatic evolutionary change recently, both in terms of their behavior and their appearance-most of them being species that interact regularly with humans; our domesticated weeds, our pests, and our pets. It has even been postulated, as John Livingston suggested in his book Rogue Primate, that our species has domesticated itself.

Possibly, one of the biggest stories in our recent evolutionary history is allele flow, that erasure of thousands of ethnic and regional differences in gene pools as individuals from one part of the world invade, migrate, settle, conquer, and interbreed. So strong has it been that there are few Native Americans that can trace pure ancestry back to the men and women who crossed Beringia. In other places, Europe and Asia, it has erased a thousand subtle regional differences.

It is essential to dismiss the misconception that evolution is teleological or goal directed. Evolution is usually gradual change brought about in a species by a statistical bias toward certain individuals more likely to survive and make a greater number of copies of themselves, as well as other random factors that create genetic variation and cause random change over time. It is punctuated by the process of speciation, another random process, that splits evolutionary lineages by creating reproductive isolation between populations. None of these processes has a conscience, a memory, or a plan. Thus, evolution does not proceed from start to finish, but rather, continuously shapes a species by a variety of factors. It is the rule, rather than the exception, for a species to evolve in one direction for a while, and then evolve in retrograde for a while, as conditions favor the types of individuals that were more common to begin with. At any given time, the effects of each evolutionary mechanism depend greatly upon the physical environment.

With a change in the environment, evolution can reverse itself or go in directions completely different from earlier trends. Thus, our evolutionary past does not predict our future. Between 1.5 million years ago, and 25,000 years ago, our lineage underwent a rapid increase in brain size. This trend continued from Homo erectus into early Homo sapiens, yet this trend need not continue. In fact, it has stopped. The best fossil evidence we have suggests that, for the last 30,000 years, our brains have gotten slightly smaller. Some of this, of course, is associated with a general decline in body size associated with the shift to farming, and away from hunting mammoths.

IQ, whatever crude measure of intellect it is, is not positively correlated with fitness, by the way, nor is it negatively correlated. Evidence suggests that the highest reproductive prowess is centered in the middle of the IQ curve. There is some positive assortative mating for IQ though, which increases the spread a bit, producing a few more IQ geniuses (as opposed to the real kind, who can compose symphonies or interpret the red shifts of quasars), than we would see otherwise. This is not to say that our brains are not evolving rapidly. Nine percent of the genes we share with chimps are still evolving quickly, some of them associated with brain development. Others are involved in perception, sperm production, and immunity.

Likely, one of the biggest agents of natural selection operating today is infectious disease. The parasites we take for granted, things like colds, the flu, chicken pox, are relative newcomers, just jumped in from the species we have domesticated. The arrival of each was probably heralded by a huge plague. My guess is that each of the great ancient plagues has its origin in the arrival of one of these, now-mundane parasites. They have evolved decreasing virulence. Whatever organism caused the Plague of Athens burned through its hosts too quickly and died out, but it probably came back, with a more patient set of genes less likely to kill the host. Along the way, it must have imposed some selection on its host as well.

In some ways, our domesticated species have domesticated us. Many of us carry the genes for lactose tolerance, and for forms of alcohol dehydrogenase that allow for a good buzz, both of which we owe to our domesticated creatures, cows and yeast respectively.

Negative selection..the directional selection against mutations that cause congenital illness, continues today, despite our couches, our store-bought food and our doctors. It is open to debate whether years of eyeglasses have caused human vision to degenerate, removing the weed-out process for bad eyesight (possibly, several world wars and an army obsessed with sending good genes into battle to be exterminated from the population, leaving the bad ones at home might have helped myopia spread, though I doubt the selective pressure has been pervasive enough for that), but things like Usher syndrome and muscular dystrophy still feel the weight of selection, pressing them like a vice, to small frequencies.

Concerning the morphological traits more familiar to us, they seem to follow a pattern similar to that of IQ. Stabilizing selection, the tendency of those in the middle of the curve to be most fit, has long been documented for birth weight. This is probably true of human body size. Very tall and very short individuals have reduced survivorship, as well as the hyper-skinny and the obese. Recent research suggests that, among women at least, those individuals that are just slightly heavier than the average have the highest fitness. Similarly, those individuals that are just slightly shorter than the average have the highest fitness. Favored also, however, are women who are able to start reproducing early, and keep going until later in life. This is all very fluid, a snapshot from one place in New England, and evolutionary trends in Botswana may very well be different.