What did members of the species Australopithecus afarensis (or, as I call them in my novel, foot-apes) look like? How did their bodies function and move?
The short answers to those questions are readily available online, and artists, such as the excellent Mauricio Anton and John Gurche, have produced wonderfully life-like depictions based on available evidence. But as a novelist I needed somewhat more and couldn’t always find it, either because nobody knows or because nobody had bothered to put the information where I could find it. After all, I ask unusual questions.
For example, what were foot-ape feet like? The pictures all give them feet like ours, but is that based on fossil evidence or not? I was unable to discover whether a reasonably complete foot of A. afarensis has ever actually been examined by human scientists. The individual known as the Dikika Baby does have feet, but at least at the time I was doing my research the feet were still embedded in the rock matrix in which she’d been found.
That foot-apes had humanlike feet would not be a bad guess, given that we know they were obligate bipeds, like us, from the shapes of their hips and knees and the angle at which their spines met their heads. There are also the footprints at Laetoli, which are generally attributed to A. afarensis, since that’s the only hominid we know was alive at the time, and those prints were made by feet like ours. But the very fact that scientists sound unsure about the attribution suggests they don’t have foot-ape feet to compare to the prints. And there could have been another australopithecine in the area we don’t know about yet.
I went with giving my characters human-like feet, but it bothers me that I don’t actually know.
Such questions arise, in part, because we really have very little material on most long-extinct species. Some are described only from a single partial skull or, in the case of the Denisovans, from DNA recovered from a single fragment of one finger. Australopithecus afarensis debuted with a comparative wealth of material–bits and pieces of 13 individuals (a few more have been found since)–but that still leaves a lot unclear.
For example, what is normal? Small sample sizes are vulnerable to random variation. If you only have a handful of examples of a species, there is a chance you could have a handful of weird individuals that aren’t representatives of their species.
Don Johanson and Tim White, who discovered A. afarensis, were initially confused by the size disparity among their finds and debated among themselves as to whether they had one new animal or two. Because the sizes formed a smooth continuum, rather than two distinct clumps, they settled on one species in which males were much bigger than females. Given the available evidence, that was a good guess, and you’ll notice I followed their lead for my book. But it’s important to notice that the evidence they had was thin.
For example, they couldn’t sex the skeletons. I have been unable to confirm whether there are skeletal differences between the australopithecine sexes besides size, but by Johanson’s account he didn’t know of any when they described the species. Possibly the bones were too fragmented, without enough copies of the same bone for meaningful comparison of shape. So we don’t actually know that foot-ape men were much bigger than foot-ape women. Maybe both sexes varied a lot in size? Maybe females were bigger? Maybe the sample really was two species mixed? We can only guess.
I don’t want this post to get too awful long, so I’ll just go through some of the other details I learned and guesses I made quickly.
Besides being bipedal, how did foot-apes move? We know their shoulder joints angled slightly upward and that their hands, though basically human in shape, had slightly curved fingers. The carpal tunnel, where tendons pass through the wrist, was very large. The proportions of their arms and legs were similar to ours (something not true of all australopithecine species), although their forearms were somewhat longer. Overall, they were very strong, rather like chimpanzees are–and chimpanzees can bicep-curl more than their own weight without apparent effort. The femoral neck, however, was much thinner, suggesting weaker hip joints. I’ve read some suggestion that their stride may have been less efficient. Their rib-cages were conical, with plenty of room for a large gut at the bottom (they ate their vegetables raw, something that requires more digestion), but I wonder whether there was as much room for lungs at the top. It’s possible they had less aerobic capacity.
All of this suggest to me a small but very strong humanoid, well able to handle objects, walk, and climb roughly the same way we do (lots of humans do climb trees!), but with some important differences. They were more comfortable hanging by the arms and had a much stronger, more secure grip. They didn’t often walk long distances–an able-bodied human in good shape generally gets bored of walking before getting tired, but that might not have been true of them. They were powerful sprinters (an anaerobic exercise–it’s possible to sprint while holding your breath) but not distance runners.
Artists tend to assume that australopithecines were hairy, the same way living apes are. Of course, we don’t know for sure. Obviously, our lineage lost its hair at some point, but when? We can actually put some boundaries on the timeline; presumably the last common ancestor between us and chimpanzees and bonobos was hairy, and genetic evidence suggests that split occurred between six and 13 million years ago. So, at the earliest, we could have lost our hair then.
We can use the same technique to estimate the time of divergence between the human body louse and its nearest relative, the gorilla body louse (no, that does not mean a human had sex with a gorilla and got crabs, though that’s possible. Another possibility is that a human hunter picked up lice from a gorilla corpse). Human body lice are not closely related to human head lice, presumably because when we lost our body hair our lice got marooned on our heads. Gorilla lice then moved into the empty niche of our pubic hair. So we lost our hair sometime before we got body lice. I don’t feel like looking up the number, but that was something like one or two million years ago. Meaning foot-apes could have been either hairy or not.
Narrowing it down further depends on knowing why are so nearly hairless, and much ink has been spilled on the subject. Ultimately, I find all of the popular explanations untenable, because they all depend on selective pressures that also operate on other species that are still hairy. So I developed my own.
My guess is that we lost most of our hair when we started using fire on a regular basis. After all, a hairy person seems more likely to catch on fire and therefore to be unwilling to risk approaching it. Perhaps a chance mutation produced hairlesses at exactly the right time among a small population willing to experiment–and using fire ended up offering a huge evolutionary advantage.
We don’t have proof of fire use until much later, but Richard Wrangham has argued that the use of fire for cooking triggered the divergence of our genus, Homo, from that of the australopithecines. By definition, we have small guts, small, weak jaws, and large brains, all exactly what you’d expect of an ape eating cooked food regularly and managing fire (a complex, dangerous task, after all!). Combining Wrangham’s logic and mine, we can say that foot-apes were definitely hairy because as soon as some of them stopped being hairy they stopped being foot-apes and became humans.
I have made two further guesses, largely for artistic reasons:
My foot-apes, as adults, have pubic hair that is darker than their body hair and adult men have a mane or crest of longer hair.
My thinking is that head hair, facial hair, and the hair of the groin and armpits all had to become genetically distinct before our general hairlessness happened, or the mutation would have made us bald all over. A contrasting color at the groin would be a useful visual marker of adulthood and might make either an open vulva or an erect penis easier to see–the sexual signal would have a nice frame, so to speak. Longer hair on the head and/or face could exaggerate the physical size of adult men, an advantage for several reasons. I am supposing that australopithecines as a group had males with either manes or beards or both, and that we descend from a species in which both sexes had manes but only males had beards. The foot-apes of the book simply show a different variation of that pattern and are not our immediate ancestor (a point being debated by scientists).
Humans differ from apes in several ways, including our genitals and breasts. Female apes are flat-chested except when nursing. Our closest relatives, the chimpanzees and bonobos, have obvious genital swellings among sexually active females. Chimpanzee (and, I assume, bonobo) males have proportionately smaller penises than our males do, and their penises retract entirely into their bodies when not erect.
Again, guessing whether foot-apes resembled us or the pannids in these respects involves asking why–and largely guessing at answers.
My guess is that permanent breasts signal adulthood. Chimpanzees, like humans, sometimes engage in inter-community violence. Both species often treat young women differently than other victims, kidnapping them rather than killing them. It might therefore be very important to be able to identify yourself as a young woman–and not an adolescent boy–very quickly. Genitals alone won’t do it, they aren’t obvious enough and might be obscured by tall grass anyway. A chimpanzee can show a genital swelling, if has one at the time, but the last common ancestor didn’t likely swell–it’s hard to imagine how such a trait would be lost, given that any female who didn’t sport her species’ sexual signal would have a hard time attracting mates. Rather than evolving swollen vulvas on our own–a bad idea for a biped–our lineage developed swollen breasts as a way to clearly identify women in war.
From an evolutionary perspective, rape is not a fate worse than death.
As to male anatomy, again it likely comes down to signaling. The penis of a chimpanzee is usually hard to see anyway, because he’s a quadruped. If he wants to show off his penis–and sometimes he does–he can sit up or stand bipedally, but at such times he’ll have an erection. When he doesn’t have an erection, it doesn’t matter what his penis looks like because nobody is looking. So he keeps it safely tucked up inside his body.
A bipedal foot-ape, on the other hand, has his penis on display all the time. He doesn’t wear clothing, we can assume. Potential lovers can size him up, as can anyone else who thinks the size of his “equipment” says anything important about him as a man (as Donald Trump recently demonstrated, perceived genital size can bear on subjects that have nothing whatever to do with sexual prowess). He has to look good naked all the time. Therefore, a penis that is visible even when flaccid, and relatively large.
Artists tend to assume australopithecines had dark brown skin, hair, and eyes. That is a good guess. The skin and eyes would have to be dark for protection from the tropical sun, just as in African apes and humans today (pale-skinned chimpazees are children–their skin darkens with age, but only children are used in entertainment and advertizing). The other African apes are all dark-haired, as are most populations of humans, too. But orangutans are famously orange, so there’s nothing about being a tropical ape that precludes other colors. And there’s nothing about being either simian or human that precludes variety–some chimpanzees have brown or grey hair, rather than the typical black. Humans vary, too. Some monkey species are very variable.
A variety of colors is neither required nor precluded by the evidence–and it’s more interesting artistically. What I settled on was a variable species, usually with hair some shade of brown, but more rarely blonde. Occasional mutations result in some families being red, black, or grey. My foot-apes use a variety of habitats and depend on group defense for safety, so they didn’t depend on camouflage. There would be no strong selective pressure against the persistence of such odd coloring.
Making It Personal
All of this is vague, species-wide information. Let’s make it more personal by supposing a single individual, a woman–a woman with dark brown hair, a somewhat thin, oval face, light-brown, almost hazel eyes, and a flock of freckles sprinkled, ebony on sienna, across the flat bridge of her nose: Semana, my main character.