Luigi Luca Cavalli-Sforza

Genes, Peoples, and Languages

The ability to learn is one of the most fundamental characteristics of life—even in very simple organisms. Culture, or the ability to learn from the experience of others, is a special phenomenon that relies on communication. The speed and the precision of communication, and even our ability to memorize what we learn, are factors that govern the efficiency of culture. Naturally, it is not enough that culture exists for it to be useful from a biological viewpoint. But several examples can demonstrate its potential value for biological adaptation. On their own, our senses of taste and smell are not enough to help us to safely choose the food we eat; we must also learn from someone else to recognize which plants are toxic and which animals are dangerous.

Culture enables us to accumulate prior discoveries and helps us profit from experience transmitted by our ancestors—knowledge that we would not have on our own. In principle, it has always been possible for a lone individual to invent differential and integral calculus starting from scratch, but the odds are very low. Even Gottfried Leibniz and Isaac Newton used existing mathematical knowledge in making these fundamental contributions. Until the invention of writing, the accumulation of knowledge was limited by human memory, which varies from one person to another. Today, this limit has disappeared. The abundance of information in the last twenty years is changing the world thanks to the rapid access modern communications provides to it. Such change was unimaginable even a few years ago.

Culture resembles the genome in the sense that each one accumulates useful informationfrom generation to generation. The genome increases adaptation to the world by the automatic choice of fitter genetic types under natural selection, while cultural information accumulates in a person's nerve cells, being received from another person and selectively retained. Cultural transmission occurs in a variety of ways: by the traditional path (observation, teaching, conversation), through books, computers, or other media developed by modem technology.

Evolution also results from the accumulation of new information. In the case of a biological mutation, new information is provided by an error of genetic transmission (i.e., a change in the DNA during its transmission from parent to child). Genetic mutations are spontaneous, chance changes, which are rarely beneficial, and more often have no effect, or a deleterious one. Natural selection makes it possible to accept the good ones and eliminate the bad ones. Cultural 'mutations' can be accidental and minor like many genetic mutations—mistakes in the copying of manuscripts in medieval monasteries, for example. Minor variation would result from the errors introduced by a scribe in copying a manuscript. Most of these errors are probably accidental, resulting from inattention. And sometimes, the scribe will take the initiative and make a change that, in his opinion, helps comprehension or the quality of the text, but that may confound future philologists.

There is a fundamental difference between biological and cultural mutation. Cultural 'mutations' may result from random events, and thus be very similar to genetic mutations, but cultural changes are more often intentional or directed toward a very specific goal, while biological mutations are blind to their potential benefit. At the level of mutation, cultural evolution can be directed while genetic change cannot.

But we inevitably arrive at the impression that most innovations are rarely truly advantageous. Sometimes the person suggesting an innovation makes a profit from it, but innovations that should improve the state of an individual, or of a social situation, often miss their mark and turn out to be unimportant, inappropriate, or even disastrous. Political history is full of examples. One of the most common errors is the exaggerated confidence in the heritability of political skill; the son of a powerful leader frequently is appointed to follow in his fathers footsteps. The effects are often very disappointing. Mendelian inheritance predicts this problem, because the similarity between parent and offspring is on average modest. History shows that hereditary monarchies last only for a short time. When stripped of genuine authority, they are often incapable of appropriately performing even their symbolic roles. Nevertheless, selection generally tends to create and maintain customs and institutions with social utility. Even if imperfect or detrimental, some cultural changes are adopted and persist, occasionally incorporating modifications based on experience. The continuous changing of customs makes us forget the original purpose of a particular practice; without history, it quickly becomes difficult to reconstruct the reasons for certain rules and social conventions. One example that deserves further research is reproductive control in economically primitive cultures, which appears to have been quite common for a long time before its post-Paleolithic decline. Then, as now among the Pygmies and perhaps all modern hunter-gatherers, pacing births helps slow population growth to manageable rates, avoiding disastrous population explosions. It was only during the Neolithic—or in general with the development of agriculture—that populations began to grow rapidly, since more people could be fed in agricultural societies. Pygmies do not like to have children more than once every four years and believe that conceiving a second child too soon after another places the first at great risk. I doubt that the Pygmies consciously realize that this provides an important restraint on population growth, and they generally offer other explanations for the custom. Demographic stasis is usually important and necessary for peaceful cohabitation of different people, but so is the ability for nomadic populations to move without the burden of carrying several small children. With an interval of four years between births only one child needs to be carried by a parent, and the population remains stationary or grows very slowly. Maintaining this four-year gap between children requires great discipline. Some researchers think that breastfeeding—by preventing ovulation—can also prevent a new pregnancy, but that does not appear to suffice. The truth is that Pygmies avoid frequent pregnancies by observing a sexual taboo for three years following the birth of a child. They make this sacrifice for the health of their children without thinking of the long-term advantages that result from this celibate period, which on its own is not likely to provide sufficient motivation. It seems to me that this sexual taboo would disappear if breastfeeding for three years were itself sufficient to prevent pregnancies. The conclusion to draw is that reasonable reproductive customs arose during the Paleolithic among hunter-gatherers that have helped them keep their demographic growth near zero, probably without their knowing or realizing it.

Every day, we face choices that may be trivial or may affect us for years. These choices are a sort of 'cultural selection.' Unlike natural selection, which chooses between the best naturally adapted individuals of a species, cultural selection proceeds through the choices made by individuals. Ultimately natural selection will operate, since it works on the cultural choices we make as well. If our choices help us reach maturity and reproduce, then our cultural decisions (as well as biological predispositions) that generated these particular choices will be favored by natural selection. Thus, each cultural decision must pass two levels of control: cultural selection acts first through choices made by individuals, followed by natural selection, which automatically evaluates these decisions based on their effects on our survival and reproduction. Every cultural decision will also be favored by natural selection if it affects survival and reproduction, creating a positive correlation between these two forms of selection.

Although culture can intervene and modify them, innate impulses were passed down to us from our ancestors, upon whom natural selection acted. Often quite strong, these impulses are rarely absent. Many of our sensations and actions are either pleasing or painful, and frequently determine our behavior.