Caveman Logic: The Persistence of Primitive Thinking in a Modern World (3 page)

So far, we have upset no one in the audience, regardless of whether seated on the extreme right or left side. What’s next? Those slight variants go forth into their environments and some of them do better than others. You might not like the idea of competition, but it is an inevitable part of life on this planet. Some of those mutations result in greater reproductive success than others, as members of the species compete with each other for precious resources. The environment is a filter, and some traits lead to greater reproductive success than their alternatives.

As Darwin argued in 1859, occasionally animals undergo sufficient change to become reproductively isolated. Geography contributes to this isolation as well. When these noninbreeding populations become sufficiently differentiated, a new species has been formed. Rats and mice are good examples: they remain closely related, but as long as we have known them they have been separate species with a common ancestor. They share physical and behavioral traits, but they also have differences in size and behavior.

And there you have it. An absolutely blind and lawful process without values or agendas. It may not be the stuff of fairy tales or creation myths, but it grinds away in its relentless way, producing outcomes. My colleague Martin Daly has stated it eloquently: “Natural selection doesn’t have goals, but it’s the reason organisms do.”
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That’s a wonderful summary of life on this planet, although the idea is a bit difficult for some people to grasp. It also doesn’t help that natural selection moves very slowly, making the concept an even more difficult sell.

True, there is no father figure/deity with agendas we can talk about in human terms. But that isn’t Darwin’s fault, any more than Newton was responsible for the law of gravity. In any case, natural selection is part of a world full of wonder, willing to reveal itself as we ask the right questions and pool our knowledge. The universe is no less thrilling as we gradually uncover its secrets and confront its mysteries. And we do so using the splendid intelligence our species has evolved. What could be more uplifting than that?

It’s worth remembering that part about copying errors. If all individuals were identical (e.g., in a cloned population), selection would be forced to stand still. All it would take is a single parasite or predator to detect a weakness and a whole population would be at risk. The Irish potato famine of the mid-nineteenth century is a widely cited example of such vulnerability. Historians often point to Ireland’s dependence on a single crop as the key to the tragedy, but it was more than that. Genetic variation could have saved the Irish potato crop. Without it, a single form of water mold (
Phytophthora infestans
) was able to destroy the crop almost overnight. Genetic variation is an essential building block for the design of well-adapted individuals, and it is also a source of resistance when a species comes into contact with predators, be they four footed or single celled. As many as 1 million people were killed by the Irish potato famine by 1850 and perhaps twice that number were forced to immigrate to the United States, Canada, Australia, and other parts of Great Britain. The expression “Celebrate Diversity” takes on new meaning when you consider how natural selection works.

Although molecular biology is well beyond the scope of this book, there are several basic things we need to cover. The collection of genes in an organism, called its
genotype
, is largely responsible for creating (with some help from the environment) the organism’s observable traits, collectively called its
phenotype
. Genes are composed of deoxyribonucleic acid (DNA). DNA contains the instructions that specify which proteins should be made. By doing this, the DNA is responsible for shaping the phenotype.

If stretched out for display, every cell in your body contains about six feet of DNA. Every nine hundred cells therefore produce over a mile of DNA. Because the human body contains as many as 100 trillion cells, our bodies house over a billion miles of DNA. That’s a pretty large number. The distance to the sun is only 93 million miles, in comparison.

We are still learning about DNA. It seems that every time we look at the human and chimpanzee genomes side by side, the degree of similarity has grown. Other than making glib statements like “Humans and chimps are more related than mice and rats,” what do we really know? As I write this in 2008, it seems the less I say about this area of research, the better. Almost anything is likely to become obsolete in short order. Craig Venter has decoded the human genome and made his own diploid genome available on the Web (
www.jcvi.org
).

We have watched estimates of the “degree of overlap” between human and chimpanzee increase from 97 percent to nearly 99 percent in the span of less than ten years. At the same time, estimates of the number of base pairs in the human genome seem to be dropping at a steady rate. Prior to mapping the human genome in 2000, estimates of the number of human genes were fixed at about 100,000. Shortly thereafter, that number fell to about 25,000, a dramatic drop by any reckoning. Had I written this book a year ago, that number would have stood at about 22,000. By the time you read this, it may lie below 20,000. The estimate keeps shrinking, yet the human genome remains firmly in place. Plainly, the number of genes is not the whole story of what makes us distinctly human.

Somewhere, somehow, there are “switches” in the genome that tell our genes when to turn on and express themselves, thus turning a genotype into a phenotype. The switches that turn genes on and off are not well understood. Some of them lie within the genes themselves. Others are thought to lie within the so-called “junk DNA,” poorly understood matter that comprises the large majority of the genome. The picture is even more complicated. In 2006, it was reported that individual differences may result from previously undetected variations in the number of times that certain key genes are copied in the genome. Preliminary findings suggest that entire sequences may be repeated as many as ten times, differing widely between individuals and yielding differences in the overall “copy number” of genes. Perhaps we have ignored material such as this or “junk DNA” for too long, focusing instead on the more obvious proteins that were easier to measure and investigate.
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In any case, high school genetics books (often called molecular biology texts in universities) are losing their resale value almost as quickly as they are published. It has become that difficult to stay current.

Our own ancestors (don’t visualize your grandfather here; try to imagine someone who lived two hundred thousand years ago) lived in small nomadic bands. A lot of inbreeding occurred and most of the persons within the band were genetically related. They made a living by hunting together and gathering nuts and fruit that grew locally. These activities were fraught with peril. Animals that were being hunted for food had no interest in being eaten. They had their own concerns about survival and reproduction and vigorously resisted our attempts to turn them into table scraps. Even nuts and berries that were available locally presented difficulties for our ancestors. “Nuts and fruit” may sound like a healthy diet today, but much of that locally grown produce had an agenda of its own that probably did not include traveling through a human digestive system.

In short, food sources were, to quote a vivid description, “scarce and antagonistic.” Food acquisition and storage were only a few of the daily problems facing our hominin ancestors.
Hominin
is the term we want here, since we’re concerned with only humans and chimps, not with the other great apes. Their survival was also threatened by environmental predators. Some of them were other humans, whose traveling bands were anything but friendly or cooperative. The study of present-day “primitive” people like the Yanomamo of the Amazon rainforest provides some insight into the perils of Pleistocene life, including competition between neighboring social groups and the kind of “spoils” a military victory entitled the winner to claim. Murder rates in contemporary cities like Detroit or Miami have nothing on so-called primitive cultures and, presumably, the Pleistocene world in which our ancestors lived.

In addition to human predators, our ancestors also faced threats from animals that viewed us as potential food sources and enthusiastically hunted us as we did them. But perhaps the greatest peril of all came from the smallest members of the living environment. Microscopic parasites represented, as they do today, a major threat to human health and survival. Imagine facing a predator that is invisible, deadly, and whose ways are beyond your understanding or control. Even if you could defend against it using some poorly understood natural remedy, the predator could mutate quickly to work around whatever paltry defense you could put in its way.

This scenario partially describes the life of our ancestors. For them, the workings of the physical world must have seemed unpredictable, unfathomable, and truly frightening. Perils were almost constant and comprehension was minimal. Keep this in mind when you’re trying to imagine the kind of mental processes that would have helped serve survival and reproduction. Understand also that much human evolution took place before there was written or spoken language. (The Sumerians invented written language around 3000 BCE.) If someone could not state his business clearly, it would have helped to be able to read his intentions and trustworthiness using other means. Long before there was spoken language, there was body language. Anyone who could send and receive it fluently was at a considerable advantage.

Something else to consider: there were no external agencies for the enforcement of right and wrong. Social rules and alliances may have been in place, but the notion of codified “laws” or individuals whose job it was to enforce the laws was unknown for much of human history. If anyone were going to detect and punish that cheater, it had better be you. Rule breaking, nonreciprocity, and cheating were major issues for our ancestors and exerted strong selection pressure on the design of their minds. Such mental “circuitry” continues to play a major part in our lives today, long after formalized social rules and legal systems have reduced the need for it.

For well over 3 million years after splitting away from the apes, our species remained largely unchanged socially, cognitively, or physically. These early hominins were not very impressive by today’s intellectual standards, although they were the best the Earth had to offer at the time.

Then something happened. Just what that something might have been remains a matter of conjecture. The results were a series of dramatic changes to our ancestors that led to a near doubling in the size of their brains and an exodus from the African continent by
Homo erectus
. Compressing 3 million years of hominin history into a paragraph or two can only trivialize or omit important events, but the bottom line is this: over this period, our species grew in stature, dispersion, and intelligence. It is the last of these that mattered most. Competition for finite resources on the planet has always included species and individuals who were stronger or more numerous than our ancestors. But the competition was never smarter.

By 500,000 years ago, our ancestors were busy defining their dominance. When we think of ourselves as a species, we are usually picturing the anatomically modern version known as
Homo sapiens
. But there is a direct line between the modern
H. sapiens
and earlier hominins like
Australopithecus
,
Homo habilis
, and
Homo erectus
. The physical changes, most notably in stature and relative brain size, occasioned a growing range of intellectual abilities.

That final 500,000 years, composing barely 10 percent of our development, was a time of many crucial changes in our species. Probably the two most important changes, in terms of what our lives have become today, were language and domestication. It is virtually impossible to overstate the importance of language in defining who we are or our range of accomplishments. Communication is widespread within the animal kingdom; language is not. Using labor-intensive procedures, we may train a chimpanzee or a parrot or a gorilla to ask for a tickle or tell us the number of items on a computer screen. But as we know and employ it every day, language remains the sole domain of our species. Indeed, getting a human
not
to learn language is quite a feat. How important is language in other aspects of human accomplishment? Make your own “Top 10” list and try to imagine any of those feats emerging without written or spoken language.

Domestication may seem an odd choice for the second most important milestone in human development but, when it occurred about ten thousand years ago, our species took a giant step forward. To bring plants and animals—essential sources of food and labor—under our control was a turning point for our species. Consider the effects of freeing our ancestors from the daily toils and perils of searching for sustenance. Now they could pursue other matters, perhaps the very things that make our species so noteworthy. Nothing on your “Top 10” list would have been accomplished if our species had been half starved or had its time consumed with hunting, berry picking, and back-breaking labor. Domestication goes well beyond pet dogs and cats.

We were not always the only human species on the planet. Most people know that other humans came
before
us but are surprised to learn that different species of humans lived at the same time. The most conspicuous example is
Homo neanderthalensis
.
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Neanderthals, who have become figures of almost cartoonlike proportions in popular culture, were actually successful competitors who lived as recently as 28,000 years ago.
H. sapiens
and Neanderthals diverged from a common ancestor about 370,000 years ago, and Neanderthals lived successfully in Eurasia for nearly 200,000 years. They were not mere brutes or scavengers, as occasionally portrayed. Evidence from 60,000 years ago indicates that Neanderthals buried their dead ceremonially with medicinal plants or flowers. Even more important, they carried a version of the FOXP2 gene associated with human language ability. Shorter and stockier than
H. sapiens
, Neanderthals eventually disappeared along with
Cro-Magnons
, our ancestors in western Europe. When we hear stories of elaborate cave paintings and burial sites in France and Spain, it is the Cro-Magnons who were responsible. In their book,
Biology, Evolution and Human Nature
, Timothy Goldsmith and William Zimmerman describe Cro-Magnons as “intellectually and emotionally very much the same as ourselves.”
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