Sex's feel-good evolution: Charles Darwin's erotic shocker

Charles Darwin got more than science right. Evolution also explains why we get it on

By David A. Rosenbaum
March 10, 2014 12:00AM (UTC)
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Margot Robbie and Leonardo DiCaprio in "The Wolf of Wall Street"

Excerpted from "It’s a Jungle in There: How Competition and Cooperation in the Brain Shape the Mind"

Declaring that your mind doesn’t have a head honcho can be scary. It violates your sense of self, your sense that you’re an individual. Seeing yourself as a conglomerate of self-interested imps rather than a clear-headed captain of your own fate can leave you feeling disoriented. Where’s your compass? How do you know which way to go?

If you think it’s scary to fire your own mental guy or gal in charge, think what it must have been like for Charles Darwin, the hero of the story to come, who suggested that no chief executive is needed to explain the formation of species, including the species to which we humans belong, homo sapiens, otherwise known as “knowing man.”


You probably know the core of Darwin’s theory, but I’ll review it here to set the stage for what’s to come. I won’t go into details about evolutionary biology. My aim will simply be to lay out Darwin’s theory as a general model for the kind of cognitive theory I wish to propose for mental function.

Darwin and the Deity

Charles Darwin was born in 1809 into an affluent British family. His grandfather was Erasmus Darwin, a well-known thinker and physician in his day.


Charles didn’t have to work for a living. Blessed as he was with the freedom to contemplate nature without having to sweep chimneys or swab floors, he could ponder at leisure the diverse forms of life he observed as he ambled through the countryside and wandered on the shore. His most famous ambling occurred on the Galapagos Islands, off the coast of Ecuador, which he visited on a voyage around the world aboard a boat called, aptly enough, the Beagle.

As a child, Darwin learned that God created the heavens and the earth. Darwin learned as well that soon after God created the heavens and the earth, God created all of the earth’s plants and animals. Finally, young Darwin learned that God created Adam and, from Adam’s rib, God created Eve. God did all this in just a few days, after which God took a one-day sabbatical and then returned to work, doing God-knows-what ever since.

Darwin would later question the authenticity of the Bible’s Creation story. Doing so took courage, for God is all-mighty. Among God’s abilities are making the sun and stars, parting the seas, forming mountains, and knowing everything that can possibly be known, even while giving people the freedom to think for themselves.


Charles Darwin was raised in a politically progressive Christian (Unitarian) family. The book in which he proposed his radical idea is one of the most famous books in the history of science, On the Origin of Species by Means of Natural Selection.

Darwin was vilified for his radical proposal. For example, in a cartoon that appeared in his lifetime, his head was drawn atop a chimpanzee’s body. But as so often happens when an author’s work stirs debate, the arguments about Origins drew a great deal of attention to the work being criticized and helped make the book a bestseller.


Darwin’s fame lived after him. He was buried in Westminster Abbey, a place where monarchs, great poets, and other famous scientists were interred. Darwin was buried there because, despite the controversy around his work, he was recognized as a truly important thinker, one whose idea could hardly be ignored. Over time, Darwin came to be hailed as one of the most important thinkers in the history of Western civilization—along with such luminaries as Newton (a fellow interree at Westminster Abbey), Karl Marx, Albert Einstein, and Sigmund Freud (none of whom lies there). The book you’re now reading is just one of many that have applied Darwin’s thinking to a domain beyond which Darwin originally intended. High tribute, indeed, to his idea!

Darwin’s Idea

What was Darwin’s idea? It was that the species of the earth can be traced to a single, original species and that all the species that have ever been here got here, stayed here, or died off through a process called natural selection.


Natural selection is a simple process. The way it works can be summarized in one sentence: Species that produce offspring tend to survive. It doesn’t hurt to state that principle another way as well: Species that don’t produce offspring tend not to survive.

“Wait a minute!” you might exclaim. “That can’t be the whole story! I could have thought of that myself !” Perhaps, but the idea has so suffused our culture that it’s hard to imagine not knowing it, at least if you’re the kind of person who reads books like this one. Being ignorant of Darwin’s idea of natural selection is nearly as unimaginable as not knowing that the earth is round. Because of hindsight bias—the difficulty of recreating what it’s like to not know something you once didn’t know but do now—you may find it incredible that there was ever a time when you or others didn’t have command of Darwin’s concept.

The elegance of Darwin’s idea is the way the story plays out, coupled with the fact that it relies on a small set of functional mechanisms and assumptions. Those functional mechanisms are three in number. They can be rattled off easily: replication, variation, and selection. The assumptions that go along with the mechanisms are sex, death, and finite resources.


Before I describe how these functional mechanisms and assumptions play out to yield the panoply of species, I should explain why I have begun this chapter by intoning God and why, for that matter, this chapter has the title it does: Darwin and the Boss. The main reason is that there is an analogy behind what I have written here and what I plan to write about later: Natural selection is to God what the jungle principle is to the mental executive. Let me explain.

The functional mechanisms and background assumptions that Darwin offered are sufficient to explain the origin of species. Saying this another way, you don’t need to invoke a divine guiding figure who designs, creates, and kills off species to explain how species originate within the Darwinian system. By the same token, you don’t need a central executive to explain how thoughts arise or die, how behaviors are chosen or suppressed, or how motives arise and subside. What I mean is that Darwin’s suggestion for the origin of species applies to the origin of mental events and the behaviors they allow. Darwin’s attempt to supplant a theistic account of the origin of the species with a self-organizing account inspires the attempt to supplant an executive-laden theory of mental phenomena with an account that eschews a mental overseer. This is not to deny that some mental processes can be called “executive processes.” That term is used by cognitive psychologists today to refer to volition. But saying that the mind as a whole acts as if someone inside directs traffic needn’t imply that there really is such an inner director.

To understand this more fully, consider the following question: How do the mechanisms and assumptions of Darwin’s theory of natural selection lead to the diversity of life forms we see? In particular, how can the observed diversity of life forms be explained without appealing to a divine being who runs the show?

A way to answer this question is to consider an imaginary world that has just one animal and just one plant. Fortunately for the plant, the animal exhales carbon dioxide. Fortunately for the animal, the plant exhales oxygen. Also, luckily for the plant, the animal poops near the plant, so the plant, through its roots, ingests essential nutrients. And happily for the animal, the plant has lots of yummy leaves that the animal likes to eat.


At first, this looks like a happy scenario. The plant and animal could go on like this for a long time—forever, perhaps, in a happily-ever-after scenario. But as in fairy tales, where the characters are supposed to live on forever but you know that’s impossible, the happily-ever-after ending for the cohabiting plant and animal is also unlikely to last long. If a strong wind comes along and blows the plant’s leaves off its branches, that’s it for the plant and for the animal too. If the animal gets stuck under a rock or freezes or drowns, that’s curtains for the animal and its leafy friend. The story ends all too suddenly. Life ceases to exist if either of these two living things perishes.

To keep things going, what’s needed is multiplicity. Many plants and animals must be on the scene. That way, nature avoids putting all her eggs in one basket. With many animals, if one of them happens to get pinned beneath a rock or happens to freeze or drown, some other animal may be able to take its place. If there are many plants and one gets plundered by flood or gets blown away by a strong gust of wind, some other plant that’s still rooted in the soil can carry on. Having many plants and animals boosts the chances that life continues. This is replication, one of the three functional mechanisms in Darwin’s theory.

Another functional mechanism in Darwin’s scheme is variation, otherwise known as diversity. Diversity allows species to be prepared, in effect, for what may happen. If all the members of a species are the same, with exactly the same capacity for lift ing themselves out from under fallen rocks, for withstanding cold temperatures, or for escaping floods, then all the members of the species will be equally susceptible to those mishaps. However, if the members of the species happen to differ in their physical or behavioral features, then some of them will be more likely to survive than others.

The term used in Darwin’s theory to refer to survival is selection. That’s the third functional mechanism in his model. Selection is vital in natural selection because it provides the means of choosing members of a species that have what it takes over those that don’t. The choosing isn’t divine. There’s no Zeus hurling lightning bolts at creatures whose time, he has decided, has come. Rather, the process is random. Organisms that happen to have features that enable them to survive tend to generate more offspring than organisms that don’t. The surviving organisms are selected-for. The others, the ones that don’t make it, are “selected out.”


Even well-adapted organisms don’t live forever. Darwin appreciated that it would be bad for organisms to live interminably. Elephants surviving endlessly would pile up. Impalas enjoying immortality would run out of running room. This is because resources are scarce. There are only so many goods to go around—only so many leaves for lunching, so many holes for hiding, and so on. Surviving requires competition for food and shelter, not to mention mates.


Mentioning mates brings up the matter of sex, which is another key part of Darwin’s theory. Why should sex exist? What’s the point of it? Te question, I realize, may sound ridiculous. “It feels good!” you may exclaim, not quite sure what planet I live on. Before you focus too much on my hedonics—no worries there, I assure you—it’s more pertinent to recall the pragmatic, less hedonistic, side of sex: Sex produces offspring. Without sex, there would be no babies, no puppies, no kittens, no cubs.

The feeling-good part of sex is, strictly speaking, not critical to its practice. Still, the hedonic (pleasure) part of sex promotes its continuation in generations to come. People don’t watch X-rated movies because they want to fantasize about wheeling baby strollers. They don’t ogle sex gods or goddesses because they’re contemplating the tax deductions they’ll enjoy by claiming more dependents. Sex, or at least the kind that comes with pleasurable moans and groans, is all about the here-and-now. When you watch Nature TV and see animals copulating, you know they’re not planning for their children’s educations. Instead, they are reveling in the buildup to oh-that-feels-good. That feeling, or the drive toward it, impels animals (including humans) to do all the strutting, prancing, dancing, and displaying that constitute courtship.


The fact that sex feels good motivates organisms to do what they do to complete sex acts, thereby generating next generations. Sex also spreads genes. If a guy has one set of genes and a gal has another, their offspring get a melange of ma and pa chromosomes. The genes the kids pick up may be good ones from dad and bad ones from mom, or vice versa. It’s impossible to tell in advance all the genes that will have positive or negative effects.

“Good” and “bad” are relative terms, defined a posterior rather than priori. Beth may have married Bud despite his dandruff , but the genes that caused Bud’s flakes may later, when expressed in Bud’s and Beth’s baby, bestow on that kid immunity to some disease. Bud may have married Beth because of her freckles, but the genes for those winsome flecks may later predispose Beth’s and Bud’s kid to get some illness no one would wish on a friend. The good or bad consequences of a gene, then, are a matter of chance. Accordingly, sex, in Darwin’s theory, has the statistical consequence of quickening chance effects. Were there no sex (or were there sex with only oneself ) the opportunity for genetic diversity would be low.

Sex or, more specifically, competition for mating provides a forum to show off features that, as far as the participants can tell, bode well for survival. In humans, clear skin may signal resistance to infection, a firm butt may signal strength, and a capacity for cool dance moves may signal agility. It’s rare for physical or behavioral features that prospective mates find appealing to be obviously bad for survival. They may not be especially good for survival once history runs its course except insofar as they are useful for attracting mates. Peacock plumes are the paradigmatic example of sexual attractants with an advantage other than attracting mates. Basso voices in human males may be another. Breasts in human females may also serve that function, for lactation in other mammals comes without swollen mammaries.

Some More from Evolutionary Biology

The Darwinian drama of individuals finding themselves more or less able to spawn offspring is a drama whose future direction no one knows or needs to know. The reason is that it can run its course without a prior plan. Indeed, there may be no plan at all.

This last point is of inestimable importance for the theory of cognition to come, especially because cognition is so much about predicting and planning. Later in this book I will suggest that what we take to be plans are just activities of neural populations shaped in basically the same way as other biological populations. Believing that we have plans need not imply that plans per se exist in our minds. Plans could be internal responses to situations (stimuli) we encounter that in turn trigger behaviors we call voluntary, intentional, or, indeed, planned.

Returning to evolutionary biology, scholars in that area of study have said much more about natural selection than I have here. My aim has just been to give the flavor of the Darwinian process in simple and, at times, fanciful terms.

Speaking fancifully is not meant to diminish the sophistication of the tools used by evolutionary biologists and their colleagues to explore the dynamics of natural selection. Those tools include studying fossils, counting organisms with different features in different environmental niches, and developing mathematical models of real and artificial life forms. With such methods, it has been possible to confirm Darwin’s theory or, saying this another way, to show that Darwin’s theory can withstand efforts to disconfirm it.  Darwin’s theory has gained so much credibility that it is possible to say it is no more speculative than Newton’s theory of gravitation.

Evolutionary biologists have also uncovered some phenomena of special interest for what’s to come in this book. I will discuss three of them here: (1) the founder effect, (2) punctuated equilibrium, and (3) niche opportunities.

The Founder Effect

The founder effect is the tendency of initial, successful occupants of a niche to have an exceptionally strong effect on succeeding generations. The effect holds when the rate of interbreeding among first settlers and their seed exceeds the rate of breeding with newcomers.

One illustration of the founder effect concerns the Amish, who live in Central Pennsylvania, where I happen to reside. The Amish live in insular communities. They mainly keep to themselves and mainly marry in-county. As a result, they enjoy less genetic variation than other, more open communities. As a further result, they have unusual traits. Due to a recessive allele shared by two members of the founders of this colony in the mid-1700s, a disproportionately large number of Amish have Ellis-van Creveld syndrome.  Individuals with this syndrome are shorter than usual, have unusually broad hands and faces, and have malformed wrists and an extra finger—a syndrome known as polydactyly. Ellis-van Creveld syndrome is traceable to two of the small number of individuals who first settled in the area that the Amish now inhabit.

The founder effect has psychological analogues. One is imprinting. Here, in the case of ducklings, the sight of a figure that may plausibly pass for Mama Duck is latched onto by recent hatchlings. They follow this figure even if she, he, or it is not their parent, provided it’s the first reasonable facsimile of a parental figure they encounter. This phenomenon was made famous by the Austrian ethologist Konrad Lorenz, who, it happens, worked with greylag geese rather than ducklings, though the phenomenon works with either species. Imprinting is analogous to the founder effect in that primary experience has extraordinary impact.

Two other psychological analogues of the founder effect can be mentioned. One is the tendency of words that are learned first to be read aloud at exceptionally high speeds—much higher than would be expected based solely on how oft en they are repeated. This has been shown both in tasks that require reading of printed words and in tasks that require naming of pictured objects.

The other psychological analogue of the founder effect is speaking a language with an accent reflecting the dialect spoken where you were raised. In my case, I was raised in Philadelphia, so I speak with a Philly accent. When I say “noodle,” I can’t help but say “neeodle.” When I say “legal,” I can’t help but say “liggle.” I can try very hard to say these words without my Philly twang, but it’s nearly impossible for me to do so. The same phenomenon occurs for people who speak English with a Russian accent, for people who speak Hebrew with a German accent, and so on. The fact that accents are so hard to shed—extensive voice coaching is usually required—attests to the founder effect for speech.

Punctuated Equilibrium

Besides the founder effect, another phenomenon of special interest from evolutionary biology is punctuated equilibrium. This is a relatively sudden change in the rate of evolutionary change. The term punctuated equilibrium refers to the fact that fossil records have shown that, in evolution, there have been periods of relative stasis or equilibrium punctuated by periods of very rapid change.

Punctuated equilibrium is important here because in mental development there are similar surges. One occurs around the age of 18 months, when in healthy human toddlers there is an explosion of language. From 18 months to 24 months, toddlers roughly double their vocabularies, from about 1,000 words to about 2,000 words.

On a faster time scale, mental states also tend to change quickly after periods of seeming quiescence. You don’t gradually see a shape, and you don’t gradually learn a fact. As is true of evolutionary states, mental states are punctuated. Minds jump from state to state, from not understanding to understanding, from not seeing a solution to seeing one. If there is a stream of consciousness, as William James suggested, the stream doesn’t flow continuously.  Rather, what you think of from moment to moment is a series of discrete realizations.

Niche Opportunities

The third phenomenon of evolutionary biology of interest here is the existence of niche opportunities . When niche opportunities arise, a species occupies a new habitat and survives within it with a low population density for a long time. Then, if conditions become more hospitable, the species proliferates.  I mention niche opportunities because an analogous phenomenon may be recognized in individual experience. If you once learned to ride a bicycle, you will always be able to do so, provided you suffer no disabling physical change. Being away from a bike for years doesn’t prevent you from knowing what to do once you recycle. The knowledge you have for bike riding is there all along and can be reawakened. Likewise for other skills.

The ability to re-engage skills that have lain dormant for years seems at first to be inconsistent with a prediction that might be made by applying the theory of natural selection to individual brains. That prediction is captured by the familiar phrase “use it or lose it.” If mental representations are untapped for long periods, the Darwinian account would seem to suggest that they should die. The phenomenon of niche opportunities shows, however, that, in the wild, species may “bide their time” if conditions for their survival are not too unfavorable. So too may neural ensembles that support long unpracticed skills, like long-ago biking or erstwhile skiing. As long as the neural ensembles supporting such skills are not crowded out by other competing elements, they can remain viable.

No Stone Goes Unturned

A last point about evolutionary theory that’s central for what’s to come can be called the “no-stone-goes-unturned” principle. This is not a phrase used by evolutionary biologists to capture a core principle in their field, as far as I know, but it’s one that, for me, captures the essential idea that nature is virtually perfectly efficient and that, by implication given the analogy I’m pursuing here, what’s good for the global goose (species) is good for the individual gander (the individual mind).

What I mean is that no potentially habitable niche goes unoccupied. Wherever living things can possibly live, they do so—under stones, under eaves, atop mountains, in the hottest deserts, in the coldest coves. Even in places where you’d least expect life to flourish, life can be found. The most salient example I know of are hydrothermal vents unfathomably deep in the sea, where there is scarcely a photon from the sun. Hydrothermal vent worms live there, comprising a life form no one knew about until its recent discovery by a deep-diving sub. So hardy are the life forms on Earth that pains are taken by NASA to ensure that no bacterium goes along for the ride to other worlds, lest extraterrestrial neighborhoods get infected by terrestrial bugs.

There’s a tie-in between the no-stone-goes-unturned principle and brain use. A claim in the popular press is that we use only 1/8 of our brains, or some such fraction. Admittedly, some people act like they use less brain power than they should. But that’s different from saying parts of their brains lie idle. Wherever neuroscientists have looked, they’ve found brain regions that are busy. As long as healthy neurons are present in an area of the brain, neurons studied there have been shown to be active. Finding a healthy region of the brain that’s completely dormant is as likely as looking under a stone and not finding a weevil, worm, or wily bacterium. The trillions of living things on Earth find places to live in every nook and cranny. If a “Vacancy” sign appears anywhere in the outer jungle, it doesn’t stay up for long. Vacancies are filled in the blink of an eye. The brain, too, provides a welcome environment for opportunistic bands of neural gnomes to flourish, as long as the living conditions aren’t too difficult. Given the hospitable environment of the brain, a wondrous diversity of neural, and then mental, life can spring up.

Excerpted from "It’s a Jungle in There" by David A. Rosenbaum with permission from Oxford University Press USA. Copyright 2014 Oxford University Press USA and published by Oxford University Press USA. All rights reserved.

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