Sexual Selection and Social Comparison
Imagine a world in which people who wanted to save for retirement were required to find someone of the opposite sex who would agree to partner with them to create a joint account. Imagine further that both parties got to draw equally from their interest-bearing account when they retired, but the rules dictated that for every dollar the man deposited into the account, the woman had to deposit a million. Finally, imagine that people could set up as many joint accounts as they desired, so long as they could find a willing partner of the opposite sex. This is an outrageous set of rules, but if such a world existed, what would you do?
Your answer likely depends on whether you’re male or female. If you’re a man, you would probably be happy to establish retirement accounts with any woman with a pulse. With that level of return on your investment, how could you lose? No matter how reprehensible she is, it’s a pretty sweet deal. In contrast, if you’re a woman, you’re in a tight spot. On the one hand, you need to create a joint account so that you can retire with some sort of savings. On the other hand, the rules of the account are stacked against you so strongly that you’re probably going to be very picky when you choose a joint account holder. He’s occasionally grumpy? Forget it. No reason to deal with a difficult joint account holder when there are plenty of nice people out there. He sings off-key? Not worth the pain and suffering. A more tuneful or quieter person will assuredly come along who’ll want to join you. And the list goes on . . .
As is evident in this example, whoever invests more resources into a joint outcome gets to call the shots when it comes to choosing a partner. The sex that contributes a smaller amount will compete for access to the investment made by the sex that contributes more, with the result that the high-investing sex will be much choosier than the low-investing sex. Robert Trivers had this insight in his famous paper on “Parental Investment,” and it turns out that it explains sex differences in mating strategies and mate competition across the animal kingdom.
In biology, the animal that produces the larger gamete (i.e., sex cell or, in this case, egg) is the female, and the one who produces the smaller gamete (in this case, sperm) is the male. For many animals, producing gametes is the sum total of their parenting effort. The female frog lays her eggs, the male frog sprays sperm across them, and then the two usually hop off into the sunset, leaving their hundreds or thousands of fertilized eggs to hatch into tadpoles and eventually grow up to be big and strong, or perhaps to be eaten by the next fish to swim by. There is no parental effort in such species beyond the act of producing and depositing eggs and sperm, yet even that degree of parenting is a significant investment.
Because the volume of biological material necessary to produce eggs is much more than that required to produce sperm, Trivers’ theory suggests that male frogs should compete to be chosen and female frogs should do the choosing. And that is exactly what happens. For example, in many species of frogs, the males sit around a pond or suitable site and croak as long and loudly as they can. The females hop back and forth to compare the volume, pitch, and duration of the croaks, and when it becomes clear who the best croakers are, the females mate with the winners.
Frogs work hard to catch enough flies to produce their eggs and sperm, but humans put frogs to shame with the amount of parental effort we devote to our offspring. It’s difficult to quantify the emotional and social energy that we put into our children, but we can calculate the biological demands. Because we’re mammals, the obligatory female investment in reproduction is substantially greater than just producing the larger sex cell. After producing the egg, human females must gestate it for nine months, with every gram of nutrition given to the fetus pipelined from the mother.
After giving birth, our female ancestors typically breast-fed their babies for another two years, with almost every calorie received by the baby being sourced from the mother. This might not seem like a big deal in a world in which the next meal is only as far away as the pantry—indeed, my wife delighted in the fact that our infant son was a human liposuction machine—but our ancestors found the caloric demand of creating and raising a baby extremely burdensome. Remember, they had to hunt down and kill or dig up and drag home every piece of food they ate.
As a result of this biologically mandated difference in parental investment, for every unit of energy that a human male must donate to produce a child, human females must donate much more than a million times as many.* This is where the joint retirement account analogy comes into play: women have more skin in the game, with the result that men tend to compete for women and women tend to be much choosier than men.
One important way that men compete for women is by showing that they will provide food, shelter, and protection for them and their offspring. Given the caloric cost of having a child, this is a major concern for women, and men have evolved to respond to this concern by showing evidence that they are good providers. Our ancestors displayed their ability to provide by being good hunters, and modern men show their ability to provide by going to college, getting good jobs, or displaying wealth. As I discuss in chapter 10, because humans form long-term, exclusive bonds in which they work together to raise their children, human mate choice is also a mutual decision. For this reason, in addition to these sex differences, there is a fair bit of competition among both men and women to get the most desirable mate.
Sexual Selection
Reproduction is the currency of evolution. If every animal had the same number of surviving offspring, there would be no evolution. Survival is important, but only in terms of living long enough to reproduce and pass your genes on to the next generation. Organisms that successfully raise lots of offspring and that facilitate the reproduction of their close relatives, pass along their proclivities into the next generation. Organisms that fail to do these things represent the end of the line for their genes, and their particular proclivities disappear from the gene pool. In this manner, traits and behaviors that are associated with reproductive success become more common than traits and behaviors that are not.
Due to this process of selection, we evolved to enjoy activities that enhance our reproductive success and dislike activities that don’t. For example, almost all adult humans enjoy sex and almost all humans find feces distasteful. It’s no surprise that having sex increases our chance of passing our genes on to the next generation, and also no surprise that eating feces decreases those chances. It’s important to note, however, that having sex and eating feces are not really parallel activities with regard to our reproductive success. Having sex has little bearing on survival but directly relates to creating offspring. In contrast, eating feces diminishes our odds of survival and thereby diminishes our chance of reproduction.*
This distinction between factors that directly impact survival and factors that directly impact reproduction was crucial for Charles Darwin, the father of evolutionary theory. If I live a thousand years but don’t reproduce, my incredible longevity is evolutionarily irrelevant. But if I live long enough to see my children through to adulthood, my survival facilitated my reproductive success. Of more direct impact is whether I can attract a mate and successfully reproduce, and hence the capacity to attract and retain a mate is of central importance in evolutionary theory. Darwin used the term sexual selection to describe the evolution of those processes that enhance our access to members of the opposite sex.
Sexual selection is a powerful force in evolution. If there is a trait that members of the opposite sex find distasteful, that trait will tend to disappear in the population (even if it facilitates survival) because owners of that trait will have trouble finding mates. For example, it’s conceivable that being a super-timid guy and hiding at the first sign of danger might have facilitated survival, but most women would have found this an undesirable trait because such a partner probably wouldn’t protect her and her children. As a consequence, there haven’t been too many super-timid guys, or at least not many who were willing to act in a super-timid way when women were around. Similarly, if there is a trait that members of the opposite sex find attractive, even if that trait diminishes our chances of survival, it can become common in the population because owners of that trait will have more mating opportunities.
This observation leads us to ask why members of the opposite sex would ever find survival-diminishing traits attractive. By way of answering this question, consider the difference between males and females of one of the most remarkable birds on the planet: peacocks and peahens. A peahen is a sensible bird, with mostly gray-brown feathers and a tail that is just a little longer than it needs to be. If you were a hungry tiger, you could walk right by a nesting peahen and never know it was there, as it would blend into its surroundings. In contrast, a peacock is an audaciously bright bird that sports the most outrageous tail in the animal kingdom. The peacock’s bright coloration would attract the attention of even a myopic tiger, and its cumbersome and heavy tail would make it much easier to catch once spotted.
Indeed, the bright and heavy peacock tail seemed like such an impediment to survival that Darwin famously wrote to the Harvard botanist Asa Gray, “The sight of a feather in a peacock’s tail, whenever I gaze at it, makes me sick!” Darwin is one of history’s greatest scientists because he had incredible insight, but also because he worked so hard to address the weaknesses in his theory. In the case of the peacock, he eventually realized that the costs of the bright color and huge tail in terms of survival were offset by the gains in reproduction. To understand why the peacock’s tail facilitates reproduction, we need to consider why certain traits are attractive.
What Does It Mean to Be Sexy?
Every organism manages the best it can, by whatever means necessary, which ensures that deception is rife among all living things. If deception helps an animal avoid predators or get a mate, then you can count on its being deceptive. My favorite deceptive mating strategies can be found in the species of birds and fish in which some of the males pretend to be females. In these species, males who aren’t large enough to fight off other males have evolved a strategy of feigning femininity, which allows them to consort with females without being challenged by bigger males. These small males then seize the opportunity to sneak an occasional copulation, thereby passing on their genes even though they would never win a fight with the larger males who are interested in the same females.
Perhaps the most extraordinary example of this strategy was witnessed among cuttlefish by Culum Brown of Macquarie University and his colleagues. Cuttlefish can change their color at will, and when they aren’t disguising themselves to match their background, females often show one color pattern while males show another. Brown was observing cuttlefish in their tanks one day when he noticed a male displaying male coloration on the half of his body facing the females, and female coloration on the half of his body facing the males. This deception allowed the two-faced male to court the females while simultaneously preventing the other males from attacking him.
Such deceptions show how animals can be dishonest to achieve their goals. No surprise here; evolution is amoral, and animals adopt whatever strategy works. But life is a coevolutionary struggle, with every organism evolving counterstrategies to deal with the strategies of their competitors. In this sense, evolution is an endless arms race, with animals developing new ways of responding whenever they are faced with novel capabilities on the part of their prey, predators, or parasites. If the balance tips too far in favor of one or the other, then extinction becomes a distinct possibility. When prey animals evolve a disguise, predators evolve greater detection abilities. If males evolve ways to deceive females into choosing them when they are a poor choice, females evolve ways of seeing through this ruse. Females who are easily duped by low-quality males are less likely to leave successful offspring in subsequent generations, so female preferences are shaped by evolution to favor males who show honest signals of quality.
An honest signal of quality is one that is impossible, or at least very difficult, to fake. For example, I can tell you about my yacht and brag about my ski vacations, but unless you’ve seen my balance sheets, you don’t know whether I’m loaded or a liar. Talk is cheap. But if I fly you to St. Moritz and scoot us around in a Maserati, that’s a much better signal that I’m well-heeled (and generous, too). I can also casually mention that I graduated first in my class at Harvard Law School, but again, I could be lying to impress you, so you’d be wise to doubt my claim. In contrast, it’s more convincing if you watch me easily solve a Rubik’s cube, as that allows you to see my brain in action. It’s more impressive still if I can solve a Rubik’s cube without looking back at it once I begin, because I’m demonstrating that I can win with a handicap.
Due to the importance of honest signals, humans are very adept at detecting even subtle cues that indicate quality. I remember one spring morning in college when I was sitting in the courtyard waiting for my friends to join me for breakfast. I happened to have a copy of the New York Times and a pen, so I decided to attempt the crossword puzzle while I waited (despite being hopeless at crosswords). As I sat staring at the first clue, pondering “Brought to tears, possibly,” an older alumnus and his family walked by. He saw me working on the puzzle and sat down to join in. I could have used his help, but before he got a chance, his wife grabbed him by the ascot and pointed out, “He’s working on the Sunday puzzle with a pen, dear. He does not need your help.” She interpreted my subsequent claims to the contrary as pure politeness, and they walked around the corner to admire the blooming trees.
A few minutes passed by and, as luck would have it, my brilliant friend Katrin plopped down next to me as I continued to wonder who was brought to tears, and why only possibly. She solved the first few dozen clues as fast as I could write the answers, at which point I realized I was now merely a scribe and shooed her away so I could give it a try. With perfect timing, the alumnus and his family passed by again, and when he tried to sit down for a second time, his wife admonished him, “Dear, he’s solved nearly half the puzzle in less than five minutes. He does not need your help.” Trying to solve a crossword puzzle with a pen is not really an honest signal, but solving it is,* and that’s why we pay attention to such details.
To return to the peacock, its bright color and extraordinary tail are honest signals of male quality because they are an enormous handicap, and that’s why the peahen finds the bright colors and huge tail so alluring. Growing a large and brightly colored tail is a bit like trying to solve the Sunday crossword with a pen. Any idiot can start the process, but it takes a pretty special organism to carry it off. Peahens are responsive to this fact, so they are attracted to peacocks who are able to survive year after year despite schlepping around five feet of brightly colored tail feathers.
A mature peacock could well be the most honest signaler in the animal kingdom, but lots of birds adopt a toned-down version of this strategy. Numerous species have long tail feathers, and when biologists artificially shorten or lengthen their tails, they find that the females respond accordingly, flocking to the long-tailed lads and shunning those who’ve had their tail feathers clipped. Not only do females of many bird species find long tails sexy, but as we saw with peacocks, color is also important. Bright colors advertise your presence to predators, so female birds can use the brightness of a male’s colors to deduce his quality. A brightly colored bird must be strong and fit to survive looking that way, whereas a dull-colored lad may well be slow and clumsy, and thus would be less suitable as a mate.
Keep in mind that female birds aren’t thinking this through. Rather, those females who prefer brightly colored males leave more offspring in the next generation, and hence pass on the tendency to prefer bright colors. The same holds true for human preferences—we don’t need to understand why we find an hourglass shape attractive in women or a triangular shape attractive in men. Evolution simply ensures that most people have these preferences.
So, birds are evolutionarily primed to prefer bright colors, but not all colors are created equal. Animal immune systems rely on plant pigments called carotenoids (such as beta carotene) to function properly, but animals are incapable of producing carotenoids on their own—they rely on plant photosynthesis to do the job for them. Animals who are struggling to fight off infections need to dedicate every bit of carotene to their immune systems, whereas healthy animals have an excess of carotenoids in their system. The reds, oranges, and yellows that many birds display on their feathers are made up of carotenoids. Because birds can afford those colors only if their immune system is robust, bright colors (particularly bright reds, oranges, and yellows) are honest signals of internal quality, even though they are being worn on the outside.
Bright reds are inherently honest signals of quality due to the metabolic cost in producing them, but there are other honest signals of quality that anyone can produce. For example, some birds have evolved to signal their dominance through the size of a black or brown patch on their chest or throat. Black feathers are no more costly than white feathers to produce, yet in these species, a larger dark patch indicates a higher position in the hierarchy. This was confusing when it was first discovered, as even the weakest males can easily grow a larger patch,* and hence it seemed that female birds of these species were falling for cheap talk.
But further study revealed that other males take these color patches very seriously, and don’t take kindly to subordinates strutting around with large dark patches as if they’re dominant. Wearing the wrong-size patch is an affront to every other male in the flock, and when biologists tested this possibility by painting larger black patches on low-status males, they essentially painted a target on their chests. Every other male in the flock will go out of its way to attack such usurpers, in an effort to show them that they’re just posers and would be wise to shrink their patch. In such cases the size of a patch becomes an honest signal, even though it can be produced without biological cost, thanks to the social consequences of wearing a larger patch than one should.*
What are honest signals of quality in human males? Size is a good indicator, as you can’t grow to be six feet tall if you’re not well nourished and healthy. Muscles are also a good indicator, as is athleticism, for the same reason. But, of course, humans care a great deal about brains as well as brawn, and markers of a good mind are also honest signals of quality. That is why women tend to find a sense of humor sexy. Not only is it fun to be around funny people, but a good sense of humor requires an agile mind to draw connections that other people find funny.
Facial symmetry is also an honest indicator of quality, as humans have evolved to be symmetric, but illnesses and accidents can disrupt that symmetry. Symmetry is a signal of health and genetic robustness (or at the very least a blessed life), and thus women tend to find it attractive. If you google “Brad Pitt” and look at his face, you’ll be struck by its symmetry. If you google “Lyle Lovett,” you’ll be struck by the indicators of a difficult life.
Symmetry, strength, height, and humor are also honest signals of quality in women, but they are not the primary markers of quality that attract men’s attention. Because being fertile is much more biologically demanding for women than it is for men, men are more interested in women’s honest signals of fertility. Most notably, men are attracted to signs of youthfulness and an hourglass shape—both signals of female fertility. If humans were like chimps in their reproductive habits, and women became more successful mothers as they aged, then no doubt men would be strongly attracted to older women. The evolution of menopause among human females has changed that equation (more on this issue in chapter 10), with the result that men are more attracted to women during their most fertile period, from their late teens to mid-thirties.*
The Theory of (Social) Relativity
Sexual selection and mate competition are the driving forces behind the power of relativity, that is, the importance of our relative standing compared to others. For example, women evolved to prefer men who are kind, generous, funny, cute, and smart; but even if I’m none of the above, they’ll still choose me if I’m their least-awful option. It doesn’t really matter how smart or attractive I am, so long as I’m smarter and more attractive than the other available men. Similarly, it won’t do me a bit of good to look like Henry Cavill and have a brain like Albert Einstein if everyone in my group is better looking and smarter. Although the chances of that are slim, the point is that our absolute levels of any given trait don’t matter that much; what matters is how we stack up against the other relevant members of our group. For this reason, people engage in social comparison all the time.
We begin this process of social comparison initially to learn about ourselves and our social standing. Am I strong or weak? Fast or slow? Rich or poor? Despite what we might think, there are no absolute answers to these questions. It all depends on how we stack up against other people. If I can bench-press more weight than the people who are close to me, I’m strong. If not, I’m weak. Our nearest neighbors are also our most important competition, so we tend to look to those closest to us to answer these questions.
The problem with this tendency to look locally is that it can lead to a very skewed worldview. I remember sitting with my friends late in our senior year of high school, reflecting on the highs and lows of the last four years. One of my friends said that her biggest regret was her lack of athletic success. She was the state champion in at least two sports, competed on the varsity team in several others, and the hardware hanging off her letter jacket would have put a Russian general to shame. I asked her how on earth she could feel that way, given that she was one of the best athletes I knew. She replied that she had failed in her dream to make the Olympic team. That aspiration may sound absurd, but two of her siblings had competed in the Olympics, so that was her standard of achievement.
We can see the effect of relativity in countless domains, and sometimes it makes perfect sense to worry about everyone else. For example, imagine I invented a pill that increased your intelligence by 50 percent, and I offered you one. Immediately after taking the pill, you’d feel so much smarter—all sorts of problems that had seemed complex before would now be child’s play. Particle physics and calculus problems would be amusing ways to entertain yourself while waiting for a haircut. But now imagine that I offered everyone else two pills. You’d be sitting there waiting for your haircut, and everyone around you would be discussing ideas that were way beyond your capacity. In a matter of moments, you’d go from feeling like a genius to feeling like a fool.
In this example, it doesn’t matter how many pills you take if everyone around you is always one pill ahead. Even if you can solve differential equations in your head, if other people are smarter, you’ll get the least interesting jobs, your friends will think you’re slow, and more generally you’ll tend to be left behind. Relativity matters in these instances. But because of the importance of sexual selection, we also get caught up in relativity when other people don’t really matter.
Consider Ilyana Kuziemko of Princeton University and her colleagues’ work on “last-place aversion.” They found that the greatest resistance to raising the minimum wage was among people who were making slightly more than that. Despite the fact that raising the minimum wage has a high probability of helping individuals who are making just above minimum wage at some point in the future, their concerns about their relative standing outweighed the potential advantages that might come from a higher minimum wage. Such reactions might seem like cutting off your nose to spite your face, but sexual selection provides the underlying logic.
Concern with relative standing has also been found in our primate cousins, and is most famously demonstrated in capuchin monkeys by Sarah Brosnan and Frans de Waal of Emory University. In their experiment, they trained monkeys to return a pebble to the experimenter after it was placed in their cage, and the monkeys were paid in cucumber slices for their efforts. The monkeys clearly regarded this payment as fair, given that they learned and sustained the appropriate behavior based on these cucumber rewards.
The critical phase of the experiment took place when the monkeys witnessed another monkey receiving a grape (a preferred food) for the same action that they were completing for a cucumber slice. If fairness is an absolute judgment, it shouldn’t matter what reward the other monkey receives for doing the same task. If a cucumber slice was good enough a moment ago, it should be good enough now. On the other hand, if fairness is a relative judgment, then it matters a great deal what the other monkey is paid.
Consistent with the logic of relativity, the capuchins working for cucumbers often refused to participate further when another monkey was paid in grapes for the same activity. De Waal shows a video from this experiment in his TED Talk Moral Behavior in Animals, and I highly recommend it, if only to see an irate monkey chuck his cucumber slice at the experimenter after the monkey next door receives a grape. At the risk of anthropomorphizing, I’ve never seen a fellow primate more outraged at unfair pay than that little capuchin.
Experiments such as this one provide compelling evidence that once your survival needs are met, everything else is relative. As we discuss in chapter 3, life was a zero-sum game in the world before cities. My fortune typically came about only as a result of your misfortune. The sad truth is that the logic of sexual selection ensures that life remains a zero-sum game even when it doesn’t need to be. If my friend gets a big raise or wins the lottery, I am indeed impoverished by his good fortune, because now it’ll be harder for me to get a mate. Prior to his achievement or good fortune, the woman I had my eye on might have chosen me. Now there’s a good chance she won’t, as he’s more attractive than he used to be.
Sexual selection etches this logic deep into our psyche, making it incredibly difficult for us to rise above it and not feel envy at the success of others—particularly the success of close others. When Sam Smith or Eminem wins a Grammy, I don’t get envious because I don’t know them, I don’t run in their crowd, and I (wisely) don’t try to compete with them. The same holds when Leonardo DiCaprio wins an Oscar; his girlfriend wasn’t going to go out with me anyway. Yet it hits close to home when my good friends outperform me, particularly in a domain I value.
My favorite demonstration of this effect is a wonderful series of experiments by Abraham Tesser of the University of Georgia and his colleagues. In a typical experiment, Tesser brought male college students into the lab to play a word game. The game was a dictionary-style task in which people passed clues to help their partner guess a target word. Tesser arranged for one participant to go first and rigged the game so that the first player always performed poorly. The key issue concerned the quality of clues that this ostensibly poor-performing participant then went on to give his partner. Some of the clues he could give his partner were designed to be really helpful, and some were designed to be really unhelpful.
To make this experiment concrete, imagine you were participating and your task was to help your partner guess the word insightful. If you wanted to help him out, you might give him the clue astute or shrewd. But if you wanted him to fail, you might give him the clue perspicacious. (Who knows what that means?) Later, if he were to complain, you could point out that if he had a half-decent vocabulary, he’d have nailed it.
Tesser found that people were more likely to give helpful clues to their partner if he was a friend rather than a stranger, but this result held only when the task was described as unimportant. When the task was described as an important indicator of verbal skills, Tesser found that after failing at the task themselves, people were more likely to give helpful clues to strangers than friends. These data suggest that good performance on the part of a friend was more threatening than good performance on the part of a stranger. It’s an ugly truth about people, but these results show that we undermine our friends when there is a risk they’ll outperform us in important domains. This is what sexual selection has wrought.