Evolution

More heat adaptations: Apart from her head, with its grooming patch of hair, her skin was all but bare. And she sweated, unlike Capo, unlike any other ape outside her species family, for bare, sweating skin was a better temperature regulator than hair for creatures destined to spend their lives in open tropical sunlight. Sweating was a paradox, for it meant Far lost water. So she had to be smart enough to find water sources to make up for that, and, unlike some of the true savannah creatures, her kind would always be tied to some extent to water courses and the coasts.

The most apelike characteristics of the pithecines — their grasping feet, long arms, and stooping gait — had soon been abandoned. Far’s feet were best fit for running and walking, not climbing: her big toe was now a toe, not a thumb. But Far’s rib cage was a little high, her shoulders a little narrow: even now her body still carried with it traces of its vanishing adaptation to the trees — as would modern humans’, as would Joan Useb’s.

Meanwhile her brain had grown to more than three times the mass of a pithecine’s, the better to handle the puzzles of a difficult landscape and the intricacies of still more complex societies of large groups of savannah foragers. That big brain was very energy-hungry, but Far’s diet was much richer than any pithecine’s, with plenty of high-protein foods like meat and nuts, which in turn required greater intelligence to gather. Thus her smartness had been driven by a virtuous circle of development.

All these changes were drastic, and yet they had been achieved by an evolutionary strategy of remarkable economy. It had been heterochrony — different timing. Walker infants looked much as their more apelike ancestors had — as would human babies — with relatively large skulls, small faces and jaws. If you wanted to become Capo, you grew your jaw large and kept your brain relatively small. But Far’s brain had grown large while her jaw had stayed small. Even the much larger size of her body had been achieved by stretching out growing phases: her body had something like the relative dimensions of a fetal Capo, inflated to adult size.

But that large body size and big brain came at a price. She had been born with her development incomplete, because that was the only way her head would have squeezed through her mother’s birth canal. She had been born premature. Unlike the apes and even the pithecines, walker infants could not forage for themselves until long after weaning: aside from their physical immaturity, the ability to exploit food sources like hunted meat, clams, and heavy-shelled nuts was not innate in the newborn, and so had to be learned. But at the same time the children of the walkers were being born into the predator hell of the savannah. So, while they were young, kids needed a lot of care.

These costly, dependent children made it difficult for the walker types to compete with the fast-breeding pithecines, with whom they often shared the same habitats. And that was why the walkers began to live longer.

Most pithecine females, like the apes before them, died not long after their fertility ended — indeed, few long outlived their last birth. Walker women, and men, began to live for years, even decades after their reproductive career was apparently over. These grandmothers and grandfathers began to play a crucial role in shaping walker society. They helped with the division of labor: They helped their daughters care for the children, they helped gather food, they were essential in passing on the complex information required by the walkers to survive.

All this had required a new efficiency in body design. Walker bodies were much better than pithecines’ at maintenance and longevity — all save their reproductive systems; a forty-year-old walker woman’s ovaries were as badly degenerated as would be the rest of her body at age eighty, if she lived that long.

Crucially, the grandmothers’ support meant their daughters could afford to have children more often. That was how the walkers outcompeted the pithecines and apes. Almost all walker children survived long after weaning. Almost all pithecine infants did not.

For the pithecines the emergence of this new form was a disaster. Walkers and pithecines were too close cousins to share the ecology easily. There were few direct conflicts between the types of people: Sometimes pithecines hunted walkers or walkers hunted pithecines, but they found each other too smart and dangerous a prey to be worth the trouble. But in ages to come the walkers — big-brained, flexible, mobile — would slowly drive their smaller-brained cousins to extinction.

Toolmaking and even consciousness were, ultimately, no guarantee of survival.