Male sexual jealousy is another example of an evolved psychological mechanism.14 Because gestation in humans and most other mammalian species occurs inside the female body, males of these species (including men) can never be certain that they are the father of their mates’ offspring, while females are always certain of their maternity. In other words, the possibility of unwittingly raising children who are not genetically their own exists only for men. The technical term for this is cuckoldry. A man is cuckolded when his wife has an affair with someone, has a child by the lover, but successfully passes the child off as the husband’s. According to one estimate, about 13–20 percent of children in the contemporary United States and 9–17 percent in contemporary Germany are not the genetic offspring of the man whose name appears on the child’s birth certificate.15 Another study shows that about 10–14 percent of children in Mexico have legal fathers different from their genetic fathers.16 Earlier estimates from the US, the UK, and France range around 10–30 percent of all children.17 As anyone who’s ever watched a daytime talk show knows, concerns about biological paternity are far from a remote theoretical possibility; in fact, anywhere from one out of ten to one out of three children are raised by men who are unrelated to them genetically.
In evolutionary terms, men who are cuckolded and invest their financial and emotional resources in the offspring of other men end up wasting these resources, as their genes will not be represented in the next generation. For this reason, men have a strong evolutionary reason to be sexually jealous, while women, whose maternity is always certain, do not. The same psychological mechanism of sexual jealousy often leads to men’s attempts to guard their mates physically, in order to minimize the possibility of their mates’ sexual contact with other men, sometimes with tragic consequences.18
While men and women present the same frequency and intensity of their jealousy in romantic relationships,19 there are clear sex differences in what triggers jealousy. The evidence from surveys and from physiological studies conducted in different cultures indicates that men become jealous of their mates’ sexual infidelity with other men, underlying their reproductive concern for cuckoldry. In contrast, women become jealous of their mates’ emotional involvement with other women, because emotional involvement often leads to diversion of their mates’ resources from them and their children to their romantic rivals.20 While recent critics of evolutionary psychology have questioned these conclusions mostly on methodological grounds,21 both strong evolutionary logic and a preponderance of empirical evidence support the clear sex differences in romantic jealousy described above.[22]
Hardwired, Not Hardheaded
Recall that evolved psychological mechanisms mostly operate behind and beneath conscious thinking. We do not consciously choose or decide to like sweets and fats. We like them but we do not know why; sweet and fatty foods just taste good to us. Similarly, we do not consciously choose or decide to feel jealous. We feel jealous under some circumstances, in response to certain predictable triggers, but we do not always know why. Evolutionary psychology contends that these evolved psychological mechanisms are behind most of our preferences, desires, and emotions, and they incline us to behave in certain ways. Evolutionary psychology explains human behavior in terms of the interaction between these evolved psychological mechanisms; the preferences, desires, and emotions that they produce in us; and the current environment in which they express themselves. This is why both biology and environment are important components of any complete explanation for human behavior, even though, for reasons we noted in the introduction, we tend to emphasize the biological factors more in this book.
Evolutionary psychology is an application of evolutionary biology to human behavior. It is characterized by the following four principles, which form very clear contrasts to the four principles of the Standard Social Science Model, which we discussed above.
1. People are animals.23 The first and most fundamental principle of evolutionary psychology is that there is nothing special about humans. They are just like all the other animal species. Now that does not mean that humans are not unique; they are. But then so are all other species. If humans are not unique, they would not be a separate species. The reason why human beings are a separate species is because no other species have exactly the set of characteristics that humans do. But the same thing can be said of chimpanzees, gorillas, dogs, cats, and giraffes. Humans are unique, but no more or no less so than fruit flies. Evolutionary psychology recognizes that the same biological laws of evolution apply to humans as they do to all other species. It therefore refutes the human exceptionalism of the Standard Social Science Model. In the words of the great sociobiologist Pierre L. van den Berghe, “certainly we are unique, but we are not unique in being unique. Every species is unique and evolved its uniqueness in adaptation to its environment.”24
2. There is nothing special about the human brain. For evolutionary psychologists, the brain is just another body part, just like the hand or the pancreas. Just as millions of years of evolution have gradually shaped the hand or the pancreas to perform certain functions, so has evolution shaped the human brain to perform its function, which is solving adaptive problems to help humans survive and reproduce successfully. Evolutionary psychologists apply the same laws of evolution to the human brain as they do to any other part of the human body. Evolution does not stop at the neck; it goes all the way up.
3. Human nature is innate. Just as dogs are born with innate dog nature, and cats are born with innate cat nature, humans are born with innate human nature. This follows from principle 1 above. What is true of dogs and cats must also be true of humans. Socialization and learning are very important for humans, but humans are born with the capacity for cultural learning, which is innate. Culture and learning are part of the evolutionary design for humans. Socialization merely reiterates and reinforces what is already in our brain (like the sense of right and wrong). This principle of evolutionary psychology is in clear contrast to the blank slate (“tabula rasa”) assumption of the Standard Social Science Model. In the memorable words of William D. Hamilton, who is often regarded as the greatest Darwinian since Darwin, “The tabula of human nature was never rasa and it is now being read.”25 Evolutionary psychology is devoted to reading the tabula of human nature.
4. Human behavior is the product of both innate human nature and the environment. Genes very seldom express themselves in a vacuum. Their expressions—how the genes translate into behavior—often depend on and are guided by the environment. The same genes can express themselves differently depending on the context. In this sense, both innate human nature, which the genes program, and the environment in which humans grow up are equally important determinants of behavior. Unlike those in the school of the Standard Social Science Model, evolutionary psychologists do not believe that human behavior is 100 percent determined by either factor. As we mentioned in the introduction, however, we will mostly focus on innate human nature, because this is the forgotten side of the equation.
The Savanna Principle: Why Our Brains Are Stuck in the Stone Age
The second principle of evolutionary psychology discussed above—that there is nothing special about the human brain as a body part—leads to an important implication. Just as the basic shape and functions of the hand or the pancreas have not changed since the end of the Pleistocene Epoch (“the Ice Age”) about ten thousand years ago, the basic functioning of the brain has not changed very much in the last ten thousand years. The human body (including the brain) evolved over millions of years in the African savanna and elsewhere on earth where humans lived during most of this time. This ancestral environment, where humans lived in small bands of 150 or so related individuals as hunter-gatherers, is called the environment of evolutionary adaptedness, or the ancestral environment.26 It is to the ancestral environment that our body (including the brain) is adapted. Even though we live in the twenty-first century, we have a Stone Age brain ( just like we have Stone Age hands and a Stone Age pancreas
).
The evolved psychological mechanism produces adaptive behavior in the ancestral environment. Adaptive behavior is behavior that increases the chances of survival or reproductive success by solving the adaptive problems. Eating lots of sweet and fatty foods, which contain higher calories, is adaptive behavior that solves the adaptive problem of procuring sufficient food to survive. Becoming jealous at the remotest possibility of a mate’s sexual infidelity, and guarding that mate so that she could not have sexual contact with other men, is adaptive behavior that solves men’s adaptive problem of paternity uncertainty.
Our hominid ancestors spent 99.9 percent of their evolutionary history as hunter-gatherers on the African savanna and elsewhere on earth. It was not until about ten thousand years ago, when the Agricultural Revolution happened, that our ancestors started planting and cultivating their food through agriculture and animal husbandry. Almost everything we see around us today—cities, nation-states, houses, roads, governments, writing, contraception, TVs, telephones, and computers—came about in the last ten thousand years. Recall that our entire body is adapted to the ancestral environment and that we have a Stone Age body (including the brain). That means that our body is not necessarily adapted for things that came about since the end of the Pleistocene Epoch about ten thousand years ago. Ten thousand years is a very short period of time on the evolutionary time scale; it is simply not enough time for our body to make changes to accommodate things that came about in the meantime, especially since the environment has been changing too rapidly relative to how slowly we mature and reproduce. (It takes humans about twenty years to mature and be ready to reproduce. And, remember, only twenty years ago, for most people outside of the military and scientific circles, there was no such thing as the Internet or cell phones.) In other words, we still have the same evolved psychological mechanisms that our ancestors possessed more than ten thousand years ago.
This observation leads to a new proposition in evolutionary psychology called the Savanna Principle,27 which states that
The human brain has difficulty comprehending and dealing with entities and situations that did not exist in the ancestral environment.
One example of an entity that did not exist in the ancestral environment is TV or any other realistic images of other humans, such as photographs, videos, or films. The Savanna Principle would therefore predict that the human brain has difficulty comprehending and dealing with images shown on TV. This indeed appears to be the case.28 A recent study shows that individuals who watch certain types of TV programs are more satisfied with their friendships, as if they had more friends or socialized with them more frequently. According to the Savanna Principle, this is probably because the human brain, adapted to the ancestral environment, has difficulty distinguishing between our real friends in the flesh and the characters we repeatedly see on TV. In the ancestral environment, any realistic images of other humans were other humans, and if you saw them repeatedly and they did not try to kill or harm you in any way, then more than likely they were your friends. Our Stone Age brain therefore assumes that the characters we repeatedly encounter on TV, very few of whom try to kill or harm us, are our real friends, and our satisfaction with friendships thereby increases by seeing them more frequently.
Maladaptive Adaptations
Take the example of our preference for sweets and fats as an evolved psychological mechanism. This psychological mechanism solved the adaptive problem of survival in the ancestral environment by allowing those who possessed it to live longer. Our preferred consumption of sweets and fats was therefore adaptive in the ancestral environment. However, we now live in an environment where sweets and fats are abundantly available in every checkout line in every supermarket, in every city, in every industrial society, twenty-four hours a day, seven days a week. In other words, the original adaptive problem (malnutrition) no longer exists; very few people die of malnutrition in industrial societies. Yet we still possess the same psychological mechanism that compels us to consume sweets and fats. Because our environment is so vastly different from the ancestral environment, we now face a curious situation where those who behave according to the dictates of the evolved psychological mechanism are worse off in terms of survival. Obesity (to which over consumption of sweets and fats leads) hinders survival. The Savanna Principle suggests that we continue to have (currently maladaptive) preferences for sweets and fats, and as a result become obese, because our brain cannot readily comprehend the supermarkets, the abundance of food in general, and indeed agriculture, none of which existed in the ancestral environment. Our brain still assumes we are hunter-gatherers with very precarious and unpredictable sources of food. If our brain truly comprehended supermarkets, we would not crave sweet and fatty foods.
Similarly, male sexual jealousy is another evolved psychological mechanism that hasn’t quite caught up to modern times. It solved the adaptive problem of reproduction in the ancestral environment by allowing men who possessed it to maximize paternity certainty and minimize the possibility of cuckoldry. Sexual jealousy was therefore adaptive in the ancestral environment. However, sex and reproduction are often separated in the modern environment; many episodes of sex do not lead to reproduction. There is an abundance of reliable methods of birth control in industrial societies, and many women use the contraceptive pill. For these women, sexual infidelity does not lead to childbirth, and their mates will not have to waste their resources on someone else’s children. Even if their mates cheated on them and got pregnant as a result, reliable paternity testing removes any paternity uncertainty. In other words, the original adaptive problem (paternity uncertainty) is less of a threat to reproductive success; men today are much less likely to invest unwittingly in someone else’s genetic children. Yet men still possess the same psychological mechanism that makes them jealous at the possibility of their mates’ sexual infidelity and compels them to guard their mates to minimize the possibility of cuckoldry. The fact that his adulterous wife was on the Pill at the time of her sexual infidelity offers very little consolation to a man.
Further, once again because our current environment is so vastly different from the ancestral environment, we now face a curious situation where those who behave according to the dictates of the evolved psychological mechanism are often worse off in terms of reproductive success. Extreme forms of mate guarding, such as violence against mates or romantic rivals, are crimes in most industrial nations. Incarceration, and consequent physical separation from their mates, does everything to reduce the reproductive success of the men. Yet men continue to exhibit sexual jealousy, and many men engage in extreme forms of mate guarding and vigilance, including violence.29 The Savanna Principle suggests that this is because their brains cannot truly comprehend effective birth control, written laws, the police, and the courts. If they did, they would not engage in extreme forms of mate guarding (such as violence) or any other criminal behavior for which they would likely go to jail.
We caution you that the Savanna Principle as stated above was proposed very recently (even though it is based on observations made earlier by pioneers of evolutionary psychology) 30 and is not yet part of the established literature of evolutionary psychology. Its implications have yet to be subjected to rigorous experimental testing. However, we refer to it throughout the rest of the book, because we believe there is a kernel of truth to it and that it can explain a wide range of otherwise puzzling instances of human behavior.
Human Evolution Pretty Much Stopped about Ten Thousand Years Ago
The Savanna Principle points to a couple of very important—but often neglected—observations about human evolution: Evolution happens very gradually, and natural selection requires a stable, unchanging environment to which it can respond.
Evolution takes many generations, and so the speed of evolution of a species is relative to how long it takes for individuals of the species to mature sexually. Evolution happens faster for fast-maturing species and slower for slow-maturing species. Fruit flies a
re one of the fastest-maturing species in nature, and humans are one of the slowest. It takes only seven days for fruit flies to mature sexually under ideal conditions, whereas it takes fifteen to twenty years for humans. It means that there can be more than fifty generations of fruit flies in one year, before a human baby can even begin to walk. There are more than a thousand generations of fruit flies in one human generation (twenty years), for which humans need more than twenty thousand years. Evolution for fruit flies can happen pretty fast, which is precisely the reason why they are the favorite species for geneticists to study. Human evolution happens much, much more slowly. No human scientists can see it in action the way they can observe fruit fly evolution unfold in the lab.
The second point is even more important: Natural selection under most circumstances requires a stable, unchanging environment for many, many generations. For example, if the climate is very cold for centuries and millennia, then gradually individuals who have better resistance to cold will be favored by natural selection, and their neighbors who have less resistance to cold (who are more adapted to hot climates) will die out before they can leave many children. This will happen generation after generation, until one day all humans have great resistance to cold. A new trait—resistance to cold—has now evolved and become part of universal human nature. But this trait could not have evolved if the climate was cold for one century (only five human generations, albeit 5,200 fruit fly generations) and then hot for another century, only to be cold again in the third century. Natural selection would not know who (with which traits) to select.
Since the advent of agriculture about ten thousand years ago and the birth of human civilization which followed, humans have not had a stable environment against which natural selection can operate. For example, a mere two centuries (ten generations) ago, the United States and the rest of the Western world were largely agrarian; most people were farmers. In the agrarian society, men achieved higher status by being the best farmers; those who possessed certain traits that made them good farmers had higher status and thus greater reproductive success than others who didn’t possess such traits.
Why Beautiful People Have More Daughters: From Dating, Shopping, and Praying to Going to War and Becoming a Billionaire–Two Evolutionary Psychologists Explain Why We Do What We Do Page 3
