A short history of nearly everything - Bill Bryson [225]
“There is simply no compelling reason we know of to explain why human brains got large,” says Tattersall. Huge brains are demanding organs: they make up only 2 percent of the body's mass, but devour 20 percent of its energy. They are also comparatively picky in what they use as fuel. If you never ate another morsel of fat, your brain would not complain because it won't touch the stuff. It wants glucose instead, and lots of it, even if it means short-changing other organs. As Guy Brown notes: “The body is in constant danger of being depleted by a greedy brain, but cannot afford to let the brain go hungry as that would rapidly lead to death.” A big brain needs more food and more food means increased risk.
Tattersall thinks the rise of a big brain may simply have been an evolutionary accident. He believes with Stephen Jay Gould that if you replayed the tape of life—even if you ran it back only a relatively short way to the dawn of hominids—the chances are “quite unlikely” that modern humans or anything like them would be here now.
“One of the hardest ideas for humans to accept,” he says, “is that we are not the culmination of anything. There is nothing inevitable about our being here. It is part of our vanity as humans that we tend to think of evolution as a process that, in effect, was programmed to produce us. Even anthropologists tended to think this way right up until the 1970s.” Indeed, as recently as 1991, in the popular textbook The Stages of Evolution, C. Loring Brace stuck doggedly to the linear concept, acknowledging just one evolutionary dead end, the robust australopithecines. Everything else represented a straightforward progression—each species of hominid carrying the baton of development so far, then handing it on to a younger, fresher runner. Now, however, it seems certain that many of these early forms followed side trails that didn't come to anything.
Luckily for us, one did—a group of tool users, which seemed to arise from out of nowhere and overlapped with the shadowy and much disputed Homo habilis. This is Homo erectus, the species discovered by Eugène Dubois in Java in 1891. Depending on which sources you consult, it existed from about 1.8 million years ago to possibly as recently as twenty thousand or so years ago.
According to the Java Man authors, Homo erectus is the dividing line: everything that came before him was apelike in character; everything that came after was humanlike. Homo erectus was the first to hunt, the first to use fire, the first to fashion complex tools, the first to leave evidence of campsites, the first to look after the weak and frail. Compared with all that had gone before, Homo erectus was extremely human in form as well as behavior, its members long-limbed and lean, very strong (much stronger than modern humans), and with the drive and intelligence to spread successfully over huge areas. To other hominids, Homo erectus must have seemed terrifyingly powerful, fleet, and gifted.
Erectus was “the velociraptor of its day,” according to Alan Walker of Penn State University and one of the world's leading authorities. If you were to look one in the eyes, it might appear superficially to be human, but “you wouldn't connect. You'd be prey.” According to Walker, it had the body of an adult human but the brain of a baby.
Although erectus had been known about for almost a century it was known only from scattered fragments—not enough to come even close to making one full skeleton. So it wasn't until an extraordinary discovery in Africa in the 1980s that its importance—or, at the very least, possible importance—as a precursor species for modern humans was fully appreciated. The remote valley of Lake Turkana (formerly Lake Rudolf) in Kenya is now one of the world's most productive