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12 Theories of How We Became
Human, and Why They’re All Wrong
Scientists have trouble agreeing on the
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https://news.nationalgeographic.com/2015/09/150911-how-we-became-human-theories-evolution-science/
BY MARK STRAUSS,
NATIONAL GEOGRAPHIC
PUBLISHED SEPTEMBER 12, 2015
What a piece
of work is man! Everyone agrees on that much. But what exactly is it
about Homo sapiens that makes us unique among animals, let
alone apes, and when and how did our ancestors acquire that certain something?
The past century has seen a profusion of theories. Some reveal as much about
the time their proponents lived in as they do about human evolution.
1. We Make
Tools: “It is in making tools that man is
unique,” anthropologist Kenneth Oakley wrote in a 1944 article. Apes use found
objects as tools, he explained, “but the shaping of sticks and stones to
particular uses was the first recognizably human activity.” In the early 1960s,
Louis Leakey attributed the dawn of toolmaking, and thus of humanity, to a
species named Homo habilis (“Handy Man”), which lived in East
Africa around 2.8 million years ago. But as Jane Goodall and other researchers
have since shown, chimps also shape sticks for particular
uses—stripping them of their leaves, for instance, to “fish” for underground
insects. Even crows, which lack hands, are pretty handy.
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2. We’re
Killers: According to anthropologist Raymond Dart, our
predecessors differed from living apes in being confirmed killers—carnivorous
creatures that "seized living quarries by violence, battered them to
death, tore apart their broken bodies, dismembered them limb from limb, slaking
their ravenous thirst with the hot blood of victims and greedily devouring
livid writhing flesh.” It may read like pulp fiction now, but after the
horrific carnage of the Second World War, Dart’s 1953 article outlining his “killer ape”
theory struck a chord.
3. We Share
Food: In the 1960s, the killer ape gave way to the hippie ape.
Anthropologist Glynn Isaac unearthed evidence of
animal carcasses that had been purposefully moved from the sites of their
deaths to locations where, presumably, the meat could be shared with the whole
commune. As Isaac saw it, food sharing led to the need to share information about
where food could be found—and thus to the development of language and other
distinctively human social behaviors.
4. We Swim in
the Nude: A little later in the age of Aquarius, Elaine Morgan, a TV documentary writer,
claimed that humans are so different from other primates because our ancestors
evolved in a different environment—near and in the water. Shedding body hair
made them faster swimmers, while standing upright enabled them to wade. The
“aquatic ape” hypothesis is widely dismissed by the scientific community. But,
in 2013, David Attenborough endorsed it.
5. We Throw
Stuff: Archaeologist Reid Ferring believes our ancestors began
to man up when they developed the ability to hurl stones at high velocities.
AtDmanisi, a 1.8- million-year-old hominin site in
the former Soviet republic of Georgia, Ferring found evidence that Homo
erectus invented public stonings to drive predators away from their kills.
“The Dmanisi people were small,” says Ferring.“This place was filled with big
cats. So how did hominins survive? How did they make it all the way from
Africa? Rock throwing offers part of the answer.” Stoning animals also
socialized us, he argues, because it required a group effort to be successful.
This
painting inspired by archaeological finds at Dmanisi, in the Republic of
Georgia, shows a female Homo erectus preparing to throw a stone to
drive hyenas away from a deer carcass.
PHOTOGRAPH BY JOHN GURCHE, NAT
GEO IMAGE COLLECTION
6. We Hunt: Hunting did
much more than inspire cooperation, anthropologists Sherwood Washburn and C. S.
Lancaster argued in a 1968paper: “In a very real sense our intellect,
interests, emotions and basic social life—all are evolutionary products of the
success of the hunting adaptation.” Our larger brains, for instance, developed
out of the need to store more information about where and when to find game.
Hunting also allegedly led to a division of labor between the sexes, with women
doing the foraging. Which raises the question: Why do women have big brains
too?
7. We Trade
Food for Sex: More specifically, monogamous sex. The crucial turning
point in human evolution, according to a theory published in 1981 by C. Owen
Lovejoy, was the emergence of monogamy six million years ago. Until then,
brutish alpha males who drove off rival suitors had the most sex. Monogamous
females, however, favored males who were most adept at providing food and
sticking around to help raise junior. Our ancestors began walking upright,
according to Lovejoy, because it freed up their hands and allowed them to carry
home more groceries.
On
an elephant that died of natural causes, archaeologists tested how fast they
could butcher meat with primitive stone tools. Each man cut a hundred pounds an
hour.
PHOTOGRAPH BY DAVID L. BRILL,
NAT GEO IMAGE COLLECTION
8. We Eat
(Cooked) Meat: Big brains are hungry—gray matter requires 20 times more
energy than muscle does. They could never have evolved on a vegetarian diet, some researchers claim; instead, our brains
grew only once we started eating meat, a food source rich in protein and fat,
around two to three million years ago. And according to anthropologist Richard Wrangham, once our ancestors
invented cooking—a uniquely human behavior that makes food easier to
digest—they wasted less energy chewing or pounding meat and so had even more
energy available for their brains. Eventually those brains grew large enough to
make the conscious decision to become vegan.
9. We Eat
(Cooked) Carbs: Or maybe our bigger brains were made possible by
carb-loading, according to a recent paper. Once our ancestors had
invented cooking, tubers and other starchy plants became an excellent source of
brain food, more readily available than meat. An enzyme in our saliva called
amylase helps break down carbohydrates into the glucose the brain needs.
Evolutionary geneticist Mark G. Thomas of University College
London notes that our DNA contains multiple copies of the gene for amylase,
suggesting that it—and tubers—helped fuel the explosive growth of the human
brain.
10. We Walk
on Two Feet: Did the crucial turning point in human evolution occur
when our ancestors descended from the trees and started walking upright?
Proponents of the “savanna hypothesis” say climate change drove that
adaptation. As Africa became drier around three million years ago, the forests
shrank and savannas came to dominate the landscape. That favored primates who
could stand up and see above the tall grasses to watch for predators, and who
could travel more efficiently across the open landscape, where food and water
sources were far apart. One problem for this hypothesis is the 2009 discovery
of Ardipithecus ramidus, a hominid that
lived 4.4 million years ago in what’s now Ethiopia. That region was damp and
wooded then—yet “Ardi” could walk on two legs.
As
the Africa climate became more arid, after about three million years ago,
forests gave way to grasslands—and our ancestors had to adapt.
PHOTOGRAPH BY MAURICIO ANTON,
NAT GEO IMAGE COLLECTION
11. We Adapt: Richard Potts, director of the
Smithsonian's Human Origins Program, suggests that human evolution was
influenced by multiple changesin climate rather than a
single trend. The emergence of the Homo lineage nearly three
million years ago, he says, coincided with drastic fluctuations between wet and
dry climates. Natural selection favored primates that could cope with constant,
unpredictable change, Potts argues: Adaptability itself is the defining
characteristic of humans.
12. We Unite
and Conquer: Anthropologist Curtis Marean offers a vision of human
origins well suited to our globalized age: We are theultimate invasive species. After tens of
thousands of years confined to a single continent, our ancestors colonized the
globe. How did they accomplish this feat? The key, Marean says, was a genetic
predisposition to cooperate—born not from altruism but from conflict. Primate
groups that cooperated gained a competitive edge over rival groups, and their
genes survived. “The joining of this unique proclivity to our ancestors’
advanced cognitive abilities enabled them to nimbly adapt to new environments,”
Marean writes. “It also fostered innovation, giving rise to a game-changing
technology: advanced projectile weapons.”
So what’s
wrong with all these theories?
Many of them
have merit, but they share a bias: the idea that humanity can be defined by a
single well-defined trait or group of traits and that a single stage in evolution
was a crucial turning point on the inevitable road to Homo sapiens.
But our
ancestors weren’t beta tests. They weren’t evolving toward something, they were
just surviving as Australopithecus or Homo
erectus. And no single trait they acquired was a turning point,
because there was never anything inevitable about the outcome: the toolmaking,
stone-throwing, meat-and-potato-eating, highly cooperative, adaptable—and
oh-so-big-brained—killer ape that is us. And is still evolving
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