“That’s crazy,” replies Brunet, who points to small teeth and other key traits that link the creature with hominids rather than apes. Some paleoanthropologists, for example, have declared Sahelanthropus to be on the line that led to gorillas, not humans. No new orthodoxy has gained enough strength yet to take over the old one. Now some researchers are arguing that human evolution looked more like a bush, with lots of species branching off in different directions. “We saw human evolution as a nice, straight line,” says Leslie Aiello of University College London. These new fossils have thrown cherished orthodoxies into question. Just last year, Michel Brunet of the University of Poitiers, in France, and his team of explorers announced that amid the sand dunes of the Sahara they had found a species between 6 million and 7 million years old: Sahelanthropus tchadensis. In recent years, paleoanthropologists have found perhaps as many as five species that are older than A. Not long ago, the oldest known hominid was Australopithecus afarensis, a species that walked the savannas of East Africa around 3.6 million years ago and is best known from one well-preserved female skeleton found in Ethiopia in 1974 and nicknamed Lucy. Yet paleoanthropologists are learning a lot about our origins. When it comes to early hominids, paleoanthropologists have to make do with a few teeth or skull fragments. Most of their bones were scavenged and scattered by hyenas or other animals, and what little remained rotted. If the earliest hominids were anything like chimps, bonobos, and other living apes, each species may have numbered in the hundreds of thousands, even millions. Such are the daydreams paleoanthropologists indulge in as they endure blazing heat, merciless sandstorms, and years of fruitless fieldwork. Perhaps they would turn your way and look you in the eye-a gaze from your most distant hominid ancestors, the first primates to split off from the other apes and begin the family that produced us. They’d probably look something like chimpanzees-about the same height, with the same coat of hair-but their flat faces and the other odd proportions of their bodies would indicate that they belong to a different species. imagine that you could drop down by an African lake some 7 million years ago and watch the parade of aardvarks, antelopes, and elephants pass by until, sooner or later, you caught sight of a group of apes. Time travel would make everything so much easier. That’s not unusual for any field of science, but the eight mysteries on the following pages are intimate ones, because understanding our origins is key to understanding ourselves.
#THE STORY OF THE HUMAN BODY THE SEVEN MAJOR TRANSITIONS OF HUMAN EVOLUTION FULL#
Age-old questions defy a full accounting, and new discoveries introduce new questions. Still, what we don’t know about our evolution vastly outweighs what we do know. Meanwhile, geneticists have compiled a veritable encyclopedia of evolution-the sequenced human genome-and within a few years they’ll be able to compare it with the genome of one of our closest living relatives, the common chimpanzee. Paleoanthropologists keep digging up new fossils of our ancestors, and some of those fossils have even yielded DNA fragments. Until a few decades ago, most of that evolutionary history was hidden from science’s view.īut these days hardly a month goes by without news of a significant discovery.
![the story of the human body the seven major transitions of human evolution the story of the human body the seven major transitions of human evolution](https://cdn.britannica.com/93/393-050-12C6DE14/increase-capacity.jpg)
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As you munch your cereal, you page through the newspaper, which you can understand thanks to a brain capable of language, abstract thought, and prodigious memory-a brain that has been expanding for 2 million years. You go to the kitchen and eat cereal with a bowl and spoon that are part of a toolmaking tradition at least 2.5 million years old. You wake up each morning and get out of bed using an anatomy that allowed your ancestors to stand upright at least 4 million years ago. Extrapolating these developments enabled the researchers to predict a third phase transition, which may be induced by the current explosion of artificial intelligence, accelerating human cognitive capacities to the next threshold required for a novel mode of language.Everything you do has a history. These phase transitions accelerated the expansion of the hominid brain, exceeding the neural capacity threshold required for the emergence of language.
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The transitions were (1) the emergence of the primate cerebral cortex, with its unique characteristic of additional cortical areas together with size expansion, and (2) the replacement of natural selection as the main evolutionary mechanism by triadic niche construction, an interactive expansion of ecological-, neural-, and cognitive-niches. The brain capacity of human ancestors underwent two phase transitions, which were supported by preadaptations during the animal protolanguage period, resulting in the emergence of human language.