Evolution

But as time went on, and Africa’s climate and habitat range fluctuated, the forest-fringe environment the pithecines favored spread: In a landscape of forest clumps, there was plenty of edge. The pithecine form had proved effective and enduring, and there had been a great churning of speciation events, a radiation of ape people.

The robust gorilla folk had abandoned the adventure of the forest fringe and had taken to the deeper green. Here they had begun to exploit a source of food for which there was little competition: leaves, bark, and unripe fruit unfit for any other hominid type to digest, and nuts and seeds too hard for other animals to crack. To adapt to this lifestyle they had, like potbellies and gigantopithecines, developed huge energy-expensive guts to process their low-quality food and heavily engineered skulls capable of driving those huge jaws with their slablike teeth.

Their social lives had changed too. In the dense forest, where there was always a supply of leaves and bark, stable groups of females came together to live off a single patch of forest. Males became solitary, each trying to maintain his hold over the females in his territory. So the males became larger than the females, and there was a premium on brute physical strength, so that each male could fight off those who would usurp him.

The gorilla-man’s kind were among the least intelligent of the hominids of his day. That big gut was very energy expensive; to balance its budget his body, in the course of its adaptation, had had to make sacrifices elsewhere. Smarts weren’t essential among the harems in the dim, stable gloom of the deep forest, and so the gorilla folk’s big primate brains, very costly in blood and energy, had dissolved.

But because the gorilla-man could be sure of sexual access to his females, his testicles were small. By comparison the skinny pithecine chimp-men had to mate as often as possible with as many females as they could, and needed the large, pendulous balls they displayed so readily, to produce oceans of sperm.

Within these basic pithecine types, the gracile chimp folk and the robust gorilla types, there were many variants. Some enhanced their bipedalism. Some all but abandoned it. Some skinnies were smarter than others; some gorilla folk were dumber than the rest. There were skinnies who used tools even less advanced than Capo’s, and gorilla types who used tools more sophisticated than the gracile pithecines’ stone flakes. There were large and small, skulkers and runners, pygmies and giants, slim omnivores and pillar-toothed herbivores. There were creatures with protruding faces like a chimp’s and others with delicate, flat features almost like a human’s. And there was much crossbreeding among the types, a proliferation of subspecies and hybrids, ornamenting the carnival of hominid possibilities.

Baffled paleontologists of the future, trying to piece this diversity together from fragmentary fossils and stone tools, would devise elaborate family trees and nomenclatures, calling their imagined species Kenyanthropus platypus; or Orrorin tugenenis; or Australopithecus garhi, africanus, afarensis, bahrelghazali, anamensis; or Ardipithecus ramidus; or Paranthropus robustus, boisei, aethiopicus; or Homo habilis. But few of the names fit the reality. And besides, the boundaries between these categories of creature were very blurred. Out in the real world, of course, such labels did not matter; there were only individuals, struggling to survive and raise their offspring, as they always had.

Most of the diverse assemblage here would be lost in time, their poor bones swallowed up forever by the forest’s voracious green. No human would ever know how it was to live in a world like this, crowded with so many different types of people. It was a bubbling evolutionary ferment, as many variants were spun off a fundamentally successful new body plan.

But none of this myriad of species had a future, for all these ape folk had clung to the forest. Their fingers and toes remained long and curved to help grab hold of tree trunks, and their legs were a peculiar compromise between the needs of knuckle-walking tree climber and those of biped. At night they would even make treetop nests like their forest-dwelling ancestors before them. And their brains never developed much beyond the size of Capo’s, and those of their cousins, the ancestral chimps, because their low-quality diet could sustain nothing bigger.