Shadows of Forgotten Ancestors

Hidden among the tangled branches and vines of the Neotropical forests are the most paternal of primate fathers. The monogamously mated males of the small titi (Callicebus sp.) and night monkeys and the tiny Callimiconidae and Callitrichidae are unique in the intensity and duration of their relations with infants … Males of these species share all parental duties except nursing, and although the extent of participation is quite variable within species, they are generally the major caretakers of infants …

Males in these species are often strongly attracted to infants. Immediately after birth, they have been observed trying to sniff, touch, or hold the still-bloody newborn, and they sometimes even lick off the covering birth fluids … Within hours of birth, males carry infants on their backs, groom them, and protect them … Large portions of a male’s day are devoted to infant care, and the most devoted fathers return their infants to the mother only to suckle …

Males also permit infants to take food from their hands and mouths … The food items shared are those that infants have difficulty obtaining or processing themselves, such as large mobile insects or hard-shelled fruit …

Fiercely protective, males will defend infants against any real or imagined threat. In captivity, tiny lion tamarin males have flung themselves against intruders as intimidating as woolly monkeys, macaques, and humans.³⁸

* Apes are bigger and smarter than monkeys, and lack tails. The apes are the chimpanzees, gorillas, gibbons, siamangs, and orangutans. The siamangs are about as closely related to gibbons as chimps are to humans.* The fact that in every human ethnic group and culture males have been on average larger than females has not escaped the notice of primatologists. It may have something to do with the penchant of men for sexism, coercion of women, rape, and harems when they can get away with it. The key question is to what extent anatomy is destiny, a point to which we will return.* Something similar happened when a number of fugitive Englishmen, without a well-established dominance hierarchy (the alpha male and his close followers had been put overboard in a small boat), along with a few Polynesian women settled tiny Pitcairn Island in 1790, after the mutiny on H M S Bounty.* Those who study chimps and bonobos, so the joke goes, are called panthropologists.

Chapter 18

THE ARCHIMEDES OF THE MACAQUES

Some ascribe this to his natural genius; while

others think that incredible effort and toil

produced these, to all appearances, easy and

unlabored results. No amount of investigation

of yours would succeed in attaining the proof,

and yet, once seen, you immediately believe

you would have discovered it—by so smooth

and so rapid a path he leads you to the

conclusion … Such was Archimedes.

PLUTARCH

“Marcellus,” in The Lives of the Noble

Grecians and Romans¹

We humans have not evolved from any of the two hundred other primate species alive today; rather, we and they have evolved together from a succession of common ancestors. As we reconstruct the primate family tree, we discover who our closest relatives are. The behavior of the primates varies so widely, even between species in the same genus, that it really does make a difference for our view of ourselves which ones are our nearest relatives.

The answer, as we’ve already described, seems to be that the chimps are our closest kin, sharing some 99.6% of our active genes. We know from DNA sequencing, as you would of course suspect, that bonobos and ordinary chimps are a lot more like each other than either of them are like us.² But 99.6% is very close. We must share many characteristics of both. (Indeed, there must be behavioral traits that we share with our most distant primate cousins.)

By using molecular and anatomical evidence, together with the record in the rocks, the entire family tree of primates can be drawn, at least approximately, and a timeline placed upon it. The evidence from the bones and from the molecules are not in perfect accord, although they are beginning to converge; in this book, we have given weight to gene sequencing and DNA hybridization data. According to the molecular evidence, gorillas branched off from the evolutionary line leading to us about 8 million years ago; the still unidentified, now-extinct common ancestor of humans and chimpanzees separated from the gorillas maybe a million years later. Very quickly thereafter, the lines to chimps and humans began evolving toward their separate destinies.³ On a planet that’s been inhabited a thousand times longer, that’s pretty recently, as recent as the last two weeks in the life of a fifty-year-old human. This doesn’t mean that humans and chimps themselves began 6 million years ago; only that our common twig in the evolutionary tree branched out then.