The Evolutionary Origin of Human Behavior

by Keith C. M. Glegg

A friend suggested that I look at this book, and its subtitle certainly suggests some value to me: “How Play and Evolution Carried Us from our Reptile Predecessors to the Storytellers We Are”. A merging of evolution, play, and storytelling -- what could be more apropos for my work? I immediately ordered it from

This book was recommended to me by a friend who knows about my studies in the role of play in the evolution of human cognition. I have been putting together bits and pieces from a broad range of books, and here was a book expressly dedicated to this topic! its subtitle certainly suggests some value to me: “
How Play and Evolution Carried Us from our Reptile Predecessors to the Storytellers We Are”. A merging of evolution, play, and storytelling – what could be more apropos for my work? I immediately rushed to the Amazon website to order a copy. When it arrived, I could hardly wait until that evening when I’d have my first chance to devour it.

The first chapter started off with a straightforward setting of the stage. The author defines his terms, explains the key factors of animal evolution that he’ll be relying on, and sets the stage for the main argument. There wasn’t anything surprising in Chapter 1, other than the author’s peculiar perceptions of evolutionary theory. It’s not that his approach is wrong-headed; but he does have an odd way of phrasing well-known ideas. I often found myself, after reading several sentences, exclaiming to myself, “Ah, he’s just talking about X!” There was this omen of things to come – this sentence:

“But what was missing is a single evolutionary theory of human behavior, accompanied by that of a brain, in which all the parts fit together naturally, including at least some suggestion of how they would have to work in order to have been crucial in human evolution, and the evolving external behavior that would have been necessary to sustain human survival.”

Yes, the writing offends a strict reader, with its run-on sentence and a tense mismatch in the first clause, but there’s something more alarming in this sentence: an overly simplistic view of the human mind. Our minds are complicated and messy kluges of different systems that sometimes interfere with each other. It would be impossible to stitch together a single theory that explains all this (other than the overarching theory of natural selection). The brain’s parts do NOT “fit together naturally” – they’re jammed together in a hodgepodge that sometimes makes mistakes. Only theoretically inclined people like physicists or mathematicians would attempt to impose a neat scheme on the brain.

I was not going to be deterred by one mistake, even one so egregious as this. I pressed on to Chapter Two – where this book met its Waterloo. The author begins by stating what he considers to be a paradox:

“If these animals are programmed in such a way as to link hunger with killing other animals, how could they have achieved and sustained the necessary reproductive capacity to avoid becoming extinct?”

Translating into plain English: why don’t carnivores eat their young? The answer is ridiculously simple: animals have a variety of mechanisms for differentiating kin from prey. A combination of visual, auditory, and olfactory cues (especially pheromones) provide the clear-cut message necessary to distinguish prey from kin. The only programming that a carnivore needs is “Don’t eat your own kin!” and the so-called paradox evaporates. But this simple concept has escaped Mr. Glegg. He devises a more complicated hypothesis to explain the matter: that parents “play” an attenuated form of killing-game with their offspring. They’re still indulging their killer instincts, but those instincts are muted. What mutes them? Perhaps Mr. Glegg explains how in a later chapter – he certainly doesn’t offer an explanation in Chapter Two.

So Mr. Glegg asks us to believe that there’s some instinctive force in the genes that mutes the killing-behavior into a kind of “play killing” – yet he implicitly rejects the simpler hypothesis that there’s an instinctive force in the genes that simply blocks the instinct to kill kin. Why he accepts genetic instinct in one case but rejects it in the simpler case, I do not know.

By the way, what prevents a carnivore from killing its mate? Do carnivore mating couples engage in play-killing, too? Again, the “don’t kill your own kin” hypothesis explains this much better than Mr. Glegg’s “play-killing” hypothesis.

Indeed, animal behaviorists have shown repeatedly that various sensory triggers control much of animal behavior. Many animals mark their territories with urine or some other olfactory agent; competitors who encounter those marks will know that they’ll have to fight to remain in the territory. Animal behaviorists have been able to fool many animals by providing simple visual, auditory, or olfactory cues on which their test subjects rely. So if animals can be so sensitive to such cues, why shouldn’t they be able to differentiate their offspring from their prey?

This is only the beginning: the author next defines this basic form of play, which he calls “primal play” as an activity between parent and young. Yes, such play does take place, but an even more important factor in the play of mammals is play among the youngsters. Indeed, in many species, the young spend more time playing with their little friends than with their parents. Yet Mr. Glegg defines his key form of play in ignorance of this important phenomenon.

Here’s another quote from the book:

“…if the animal eats small lizards, its play can be expected to look like an animal killing a small lizard, and not like a lion trying to kill a zebra.”

This makes great sense at first glance, but one need only consider the domestic cat to realize just how wrong this statement is. Cats hunt small animals like lizards and mice. Cats never tackle prey anywhere near their size. Yet the play of kittens involves much tackling, rolling around, and wrestling. Adult cats do not tackle their prey, they don’t roll around on the ground while fighting it, and they do not wrestle with it. How could Mr. Glegg have missed such an obvious point?

Next, Mr. Glegg discusses what he calls “exercise play”, which he describes as “apparently pointless exercise activity”. My guess is that he’s talking about gamboling among herbivores. Since such play cannot possibly fit into his hypothesis about play being some sort of muted play-killing, he dismisses as “unnecessary”, “a way of employing excess food”. I shook my head in dismay upon reading this: the gamboling play of horses, sheep, antelopes, and other large prey animals has long been understood to be the means by which the young master the skills of escape and evasion. Why, for example, do calves kick up their heels while playing? Because it’s a last-ditch defense against a predator who is immediately behind the prey animal. This is not some dark secret that has been hidden for years -- it’s easy to find with Google.

The bloopers just keep coming. Mr. Glegg discusses in detail the evolutionary factors that discourage animals from eating their own eggs. Apparently he is unaware of the fact that malnourished animals don’t lay eggs or bear young. Indeed, some species carry out a kind of natural abortion during times of starvation, re-absorbing the nutrients of their still-gestating young or eggs.

Here’s another jaw-dropping claim:

“…as soon as human societies begin to produce more food than they need, they begin to produce less children.”

Talk about getting it exactly backwards! It’s absolutely beyond doubt that birth rates in starving societies are greatly depressed, because mothers cannot get enough calories to support the metabolically expensive process of gestating a fetus. If they do give birth, a low-calorie diet often leads to the death of the child, and if the child survives, it will likely be mentally and/or physically handicapped. As the food supply increases, women have more children who have a greater chance of reaching adulthood. The fertility rate continues to increase with the availability of food. I suspect that Mr. Glegg is referring to the well-established fact that the birth rate starts to decline in wealthy societies. This has nothing to do with calories – the reasons are controversial, but most explanations revolve around factors such as educational opportunities for women, availability of birth control, greater urbanization, and reduced dependence upon males.

I’m not done yet -- here’s another blooper: the claim that herbivore play is an evolutionary vestige, rather like the appendix in humans:

“…since primal play is certainly hereditary at this point of the mammal’s evolutionary development, some version of such behavior might continue to be transmitted from one generation to the next, even in those mammals that subsequently become plant-eaters.”

In other words, herbivores play only because their ancestors were once carnivores. But what about herbivores who have no carnivores in their evolutionary history? Mr. Glegg never addresses this problem.

I really must bring this long-winded review to an end, so I’ll conclude by exposing his treatment of the evidence. He points out that his hypothesis makes a clear prediction: that herbivores (I cannot understand why he insists on writing “plant-eating” and “animal eating”) will not play and some carnivores will play. He then looks through the evidence. He correctly notes that fish and reptiles do not play. Neither do amphibians, but he doesn’t mention that. For birds, he acknowledges that his hypothesis predicts that carnivorous birds should play, but finds only a small scrap of evidence to support his claim. There is in fact very little evidence of play by carnivorous birds, but he brushes the dearth of evidence aside with the claim that behavioral researchers probably don’t know how to recognize primal play when they see it.

He really goes overboard in his discussion of the primates. He lists seven broad categories: gorillas, orangoutangs, gibbons, rhesus macaques, chimpanzees, baboons, and humans. This sequence, he notes, is one of increasing carnivory: gorillas are exclusively herbivorous while humans have the greatest amount of meat in their diets. He therefore predicts that we will see more play as we move through this sequence. He provides evidence to support his claim, and confidently pronounces that his hypothesis has survived a harsh test.

The problem is that he’s faking the evidence. Simply google the words “gorilla” and “play” and, after you get past the playground equipment, you’ll find plenty of evidence about the extensive play behaviors of these exclusively herbivorous creatures. The same thing goes for orangoutangs.

Thus, the evidence plainly refutes Mr. Glegg’s hypothesis, but he shoves that aside and presses on.

I hope you can understand why I abandoned reading this book after Chapter Two. I figured that anybody who could make such egregious mistakes, demonstrating such towering ignorance of the basic facts, could not possibly have anything worth my time to read.