You may know koko as a huge, happy, captive gorilla who uses some sign language. She is 44 years old now. She lives in California. She likes kittens. She even understands the birds and the bees and can help plan her parenthood—or at least that's what a popular YouTube video would have us believe.

In the video, Koko's caretaker, Francine “Penny” Patterson, presents the gorilla, who is too old to give birth herself, with a notepad outlining four scenarios by which she could become a mother. A group of gorillas—one adult male, two adult females and a baby—could come live with Koko and her adult male companion, Ndume, Patterson tells Koko. Alternatively, a newborn and one or two older babies could join them; in a third scenario, just a single infant could be added. The fourth option, she explains, is that two adult females could be brought in to make babies with Ndume for Koko. Patterson hands the list to Koko, who stops scratching her chest and appears to contemplate her decision. With her right index finger, Koko taps at the last option on the notepad. “Very good idea because it would make Koko happy and it would make Ndume happy,” the caretaker tells the gorilla.

So there we have it: Koko must know how babies are made. Why else would she choose baby makers over an actual baby?

It is popularly assumed that animals know all about where babies come from. In Koko's species, the sexually mature silverback males jealously guard so-called harems of females against other males. And victorious challengers often kill the infants sired by the defeated silverback before settling down to make their own. Furthermore, the gorillas avoid inbreeding between close kin by having individuals that reach reproductive age leave their family to go find a new one.

Gorillas hardly hold a monopoly on strategic sexual and parenting behaviors. Hens eject undesirable sperm before it fertilizes their eggs. Baboon dads step into the fray when their kids need social and political support. Some females holler when copulating with alpha males but not low-ranking ones—a means of advertising their attractiveness to other influential consorts. Everywhere we humans look, creatures are behaving as if they understand exactly what sex accomplishes, how they are related to potential mates as well as offspring, and how crucial it is to continue their line—with winning genes to boot. We love to narrate observations of animal sex and parenting with language that implies common ground between them and us. But do other species actually know that it is sexual intercourse that produces babies? Does Koko?

Animal minds

In fact, there is no literature on whether animals understand reproduction. Scientists' best chance of finding out what animals know about how the world works comes from research conducted by primatologist Daniel Povinelli of the University of Louisiana at Lafayette on what nonhuman primates (the animals most like us cognitively) could fathom about physics and other areas involving cause and effect. In his books Folk Physics for Apes and World without Weight, Povinelli describes decades of experimental work aimed at understanding what apes know about gravity.

Some chimpanzees can be successfully trained to sort objects by the effort required to lift them. But when they are then instructed to sort objects from heavy to light without lifting them first, the chimps perform no better than by chance—evidence that their comprehension does not arise from actually thinking about weight. As Povinelli puts it, the chimps' ability stems from physical smarts, not cerebral smarts.

To comprehend unobservable phenomena such as gravity or impregnation, a creature has to be capable of abstract reasoning, the ability to mentally form representations of unseen underlying causes or forces. Humans use abstract reasoning to transfer knowledge from one situation to another, which allows us to solve problems we have never encountered before and to even invent new diversions for ourselves. Although animals such as chimpanzees are far cleverer than scientists have traditionally acknowledged, they do not appear to have this particular cognitive skill. I'm reminded of the time an astute sixth grader answered my question about “Why don't chimps play baseball?” not with their anatomical incompatibilities but with “Because you can't explain the rules to them.”

Of course, just because researchers have yet to detect abstract reasoning in apes does not necessarily mean it is absent. Let us say for the sake of argument that apes do have this ability. In that case, individual apes would all still have to independently discover that sex leads to babies, or they would need to share this reproductive knowledge using some form of language. Which brings us to our next problem. Other species do not have the gift of gab.

Koko can, as a result of years of training, name hundreds of objects when prompted, but she does not engage in discussion. Without her ability to sign, you probably would not be tempted to describe Koko's native verbal communication skills as sophisticated. Gorillas grumble in the presence of large amounts of food, they grunt as they approach one another or separate from their young, they make copulatory grunts, and they chuckle when they play. Primatologists Alexander H. Harcourt and Kelly Stewart, both then at the University of California, Davis, have studied these vocalizations in mountain gorillas (which are fundamentally similar in lowland gorillas, Koko's kind) and found that they are no more complex than the threat displays gorillas make in the heat of the moment. Their utterances telegraph social status and potential near-future behavior of the vocalist, but that is all.

Indeed, limited verbal skills are the norm among wild primates. Vervet monkeys have what is perhaps the closest thing to human language, and it does not begin to measure up in its complexity. As Dorothy Cheney and Robert Seyfarth of the University of Pennsylvania have observed from their extensive studies of these animals in East Africa, the vervets make distinct predator alarm calls for “eagle,” “snake” and “leopard.” These buzzy shrieks or “words” are not learned like human words but are innate. Although the alarm calls are arbitrary, like our words, they are never used to gab about a snake they saw yesterday or to fear-monger about a leopard they may encounter tomorrow. Even if one argued convincingly that these calls are monkey words, it is difficult to get from that rudimentary “language” to one in which the speaker can explain, “When we have sex, that's what starts a baby growing.”

Moreover, there is no evidence to suggest that animals have a concept of time that would allow them to link a cause such as intercourse with such a delayed effect such as a baby and to plan accordingly. Orangutans, bonobos and chimpanzees have all been observed saving tools for future use. The most sinister is Santino, a chimp at a Swedish zoo, who hoards piles of rocks under a mop of hay for tossing at visitors when they least expect it. But present observations of so-called future planning in apes are hours or a few days at most—not nearly long enough to span their gestation period, which is nearly as long as that of humans.

If animals lack the abstract reasoning, language and future planning capabilities needed to intentionally procreate, then they must know what to do (have sex) even if they do not know why (that having sex is what allows them to produce offspring and perpetuate their species). Indeed, animals may carry out all kinds of seemingly complex behaviors without actually anticipating the outcomes. Cognitive scientist Sara Shettleworth of the University of Toronto points to the example of crows that drop walnuts on hard surfaces and thereby break the nuts open. Many observers assume that the crows consciously perform this behavior with the aim of obtaining food. But a more scientific approach to understanding the nut cracking, Shettleworth notes, is to assume the cause is “proximate”: the bird's internal physiological state—hunger—is linked to the presence of walnuts and hard surfaces. That is, physiology that encourages conditioned food-procurement behavior based on past success is what causes a crow to fly above hard surfaces and drop nuts, not the crow's logic about how to best satiate its hunger.

Looking to proximate causes for animal behavior is a difficult concept for humans to accept. We assume that because we know why we do things, other animals doing something similar must also know, and we anthropomorphize their behavior. But that kind of reasoning lacks the rigor needed to truly understand animal cognition.

It is more logical to explain gorilla behavior, and indeed most of the things that animals do, without attributing to them any of our powers of imagination, especially where baby making and biological paternity are concerned. Consider the silverback who kills his new consort's offspring by another male. Infanticidal silverbacks can get more of their genes into future generations of gorillas than noninfanticidal ones. So if there is any biological basis for this complex behavior or for learning it, or both, it is passed on to their sons, who may repeat their behavior, and to their daughters, who may produce sons that exhibit it. These silverbacks must display less aggression around their kin and vice versa around non-kin, and this selectivity could be aided by familiarity over time. By the time the new silverback sires infants of his own, he has lost the urge to kill them, maybe because of behavior-influencing hormones that are communicating between his body, the babies and their mothers. No aspect of this phenomenon requires any reproductive or paternity knowledge on their part.

If they only knew

If we could somehow teach our great ape cousins that sex produces babies, then we might expect their behavior in the wild to change dramatically. Males and females that wanted offspring might start collecting semen and manually inserting it. Males might also stick around longer after coitus, potentially until birth, and then remain with the baby and mother until the youngster is old enough to live independently. Females might become more competitive for mating opportunities with males they prefer. If forced to mate against their will, they might even attempt to abort the pregnancy. Females who wanted to avoid pregnancy might hide themselves away during their estrous period, when they are fertile and attract the most male attention.

Knowing where babies come from would lead to an understanding of how individuals are related, which would have its own behavioral consequences. Both males and females might begin to take an interest in the reproductive behavior of their mature offspring and perhaps start positioning their family in the society when offspring are still immature so as to help them eventually land an elite mate. They might even prevent youngsters from leaving the group at reproductive maturity so they could better influence their reproductive lives. Brothers and sisters, knowing they come from the same parents, might also form tighter and more enduring relationships than they are known to do in these species. Aware of their relationship to offspring that mate with individuals in other groups and produce babies of their own, apes would probably show decreased competition and violence between groups that might have normally been enemies but are now understood to be blood-affiliated.

In other words, if apes comprehended that sex leads to babies, they would act a lot more like people. Which brings us back to Koko. I didn't just watch that one film of Koko. I watched many others, and in so doing I noticed that Koko practices her signs and learns new ones by exposure to symbols on a notepad. It seems that each time a symbol is presented to her she taps it with her finger first, whether she can recall and perform the correct sign or not. Koko's motherhood choice, then, did nothing to demonstrate that she understood the question, let alone baby making.

No matter how passionate or nurturing it is, nothing about the sexual, social and parental behavior of animals requires knowledge of reproduction. In contrast, much about Homo sapiens behavior does. Somewhere along the line, our species developed cultures rich in beliefs about procreation, family and connectedness—beliefs that in many ways set us apart from our ape cousins and indeed every other creature on the planet.