Upright: The Evolutionary Key to Becoming Human - Hardcover

Craig Stanford is co-director of the Jane Goodall Primate Research Center and associate professor at the department of anthropology, University of Southern California. His previous books are: Significant Others: The Ape-Human Continuum and the Quest for Human Nature (Basic, 2001), The Hunting Apes: Meat-easting and the Origins of Human Behavior (Princeton U. Press,1999), and Chimpanzee and Red Colobus: The Ecology of Predator and Prey (Harvard U. Press, 1998).

PREFACE

BABY STEPS

I remember vividly the first time that each of my three children took her or his
first unassisted steps. My firstborn had been "cruising" for weeks — pulling
herself up and walking while holding on to furniture, people, dogs, and
anything else that she could grab. But at ten months she was ready to be a
biped. She stepped away from my hands and walked several lock-legged
goose steps into her mother"s arms. My daughter"s wide eyes showed her
shock at the performance. We beamed, imagining that our parenting skills
had something to do with teaching her this most natural of all uniquely
human acts. Three years later we were living in a village in rural Mexico and
obsessing about the diseases that our younger daughter was contracting by
crawling in the dust. Then one day she stood up and toddled, and that was
that. My son was a different story; I was in East Africa, having left on a
month-long trip knowing I would likely miss the big event. Sure enough,
shortly after I arrived in Uganda, I learned through the crackling static of a
phone call that Adam, after much frustration at trying to carry a ball while
crawling, had simply stood up and walked, the ball in his arms and an ear-to-
ear grin of accomplishment on his face.
Few of us appreciate our history of becoming bipeds, perhaps
because walking requires so little energy or thought. Most of us think that our
exalted intellect or our ability to grasp with our thumbs is what sets us apart
from the other primates. But all primates share the grasping thumb, and the
difference between an ape"s brain and our own is not as great as people
think. Some parts have undergone a critical reorganization, such as the
speech centers, but a human brain is basically a ballooned version of a
chimpanzee brain.
Our ability to stand and walk habitually on two feet, however,
represents a fundamental change from the kind of creatures that our
ancestors were. Bipedalism preceded the expansion of brain size by about
five million years; it truly announced the dawn of humanity. Becoming bipedal
made us human. Whenever a fossil human is discovered, the first piece of
crucial information that everyone wants to know is "Did it walk upright?" The
second question is "How will it change our family tree?"
To an extent unappreciated by most of us, walking is sexy. It is
the key part of a cascade of traits that evolved together in an intricate mosaic
of ape and early human features. For instance, walking on two legs rather
than four released our bodies from the constraints of the synchronized
breathing gait that so many other animals, such as dogs and horses, live by.
Once the lungs of our two-legged ancestors were freed, they could modulate
their breathing in subtle ways that may have contributed to the evolution of
speech. The connection between walking upright and speaking is one of
many vivid examples of the jigsaw-puzzle evolution of our bodies.
Why we are bipedal is not simple to explain. In this book I show
that the question really consists of two parts: what made our ancestors take
their first steps, and what the evolutionary impetus was for those "toddlers" to
become highly efficient marathon walkers and runners. The first steps were,
according to the latest research, mere shuffles that helped our simian
ancestors reach plant foods such as figs that were just beyond their grasp.
Then these marginal bipeds found a light at the end of the endless search-for-
energy tunnel: meat. The meat came in the form of both small game animals,
which could be captured and eaten raw, and the carcasses of animals, both
small and large, for which the Promethean humans fanned out in search of
each day.
Meat eating provided a new and crucial source of protein, fat, and
calories that may have enabled the evolution of bigger brains and helped our
cognitive abilities to evolve. As meat eating became more important, our
ancestors adopted new ways of life that resulted in a hominid that began to
rule the planet. Being bipedal did not, contrary to popular conceptions, lead
directly to brain expansion; the two events occurred millions of years apart in
evolutionary time.
The traditional view of human origins goes something like this: Six
million years ago an ape ancestor left the comfort and security of the African
forests for life on the savanna. Its new home offered many opportunities for
advancement — including open country and a meat-rich diet that the old
home lacked. The ape evolved a means of travel in which standing upright
became not just a quick periscope but a way of life. Upright posture allowed
our ancestors to carry tools, chunks of butchered carcass, and even babies.
But the trade-off was enormous. Predators of every shape and size, from
leopards to saber-toothed cats, wandered the grass searching for prey all day
and night. The new stance left the emerging human without a means of
rapidly escaping predators. The single advantage that allowed early humanity
to survive, and turned the tide in favor of our lineage, was a rapidly expanding
brain. Armed only with its wits, the runty little human eked out an existence
for millions of years, eventually prospering and sending its progeny into the
present as big-brained Homo sapiens.
The familiar image of our ancestors" progression through stages of
hunched-over, shuffling, apelike creatures into humans is an appealing one,
but each of its elements is being called into question. The idea that we
slowly evolved toward perfection is as wrong as it is entrenched. Animals
don"t evolve toward anything; natural selection molds them generation by
generation. At each stage the animal"s form must be efficiently designed so
that it may succeed at eating, rearing offspring, and so on, or natural
selection eliminates that animal"s genes from the next generation. We are
not at the apex of life"s intricate evolution from our ape forebears, no matter
what both popular and scientific accounts claim.

BIPEDS ARE BIZARRE

Standing on two feet is a bizarre posture and an even more bizarre way to
walk. Of the more than two hundred species of primates on earth today, one
is bipedal. Of more than 4,000 species of mammals, one — the same one —
is fully bipedal when walking (a few oddities such as kangaroo rats and
meerkats stand bipedally for a few moments at a time). If we include
thousands more kinds of animals — such as amphibians and reptiles —
walking on two feet emerges as the most unlikely way to get around.
Kangaroos and birds such as ostriches and penguins are bipedal — sort of.
But they are built on an entirely different body plan and are not, strictly
speaking, reliant only on their legs for transport. Even if we throw in all the
extinct forms of terrestrial animal life, such as Tyrannosaurus rex and its kin,
the percentage of bipeds is still remarkably small. And birds and dinosaurs
differ markedly in their brand of upright posture. Most birds have stiff and
relatively short tails. They maintain stability by having their center of mass far
forward from the pelvis; this forward gravity center necessitates standing with
the upper leg bone bent. Birds that have adopted flightlessness, like
ostriches, generate their power stride by rotating the lower leg around the
knee joint. Upright dinosaurs like Allosaurus or Velociraptor opted for a
center of gravity near the pelvis and rotated their entire leg during striding.
The reason that upright posture and walking arose is the most
fundamental question in human evolution. It begets critical puzzles, such as
why bipedalism hasn"t evolved many more times, and whether the evolution of
our unique posture and gait is connected to our massive brain and
extraordinary intelligence.

In this book I emphasize that humankind is only a twig on an evolutionary
bush rather than the top rung of an evolutionary ladder of excellence. The
fossil record for the rise of bipedalism has just begun to tell us that even as
protohumans diverged from the apes, bipedalism existed in a variety of forms.
In 2000, for instance, researchers in Kenya announced the discovery of an
early human fossil that they named Kenyanthropus platyops, which appears
to have been a contemporary of other early human species, such as that to
which the famous fossil human commonly known as Lucy belongs. Until that
discovery, we believed that our family tree had only one trunk. An even more
recent and controversial find, "Toumai," is a primitive fossil from the Sahara
Desert that some experts believe represents the earliest known member of
the human family.
These are heady times in fossil hunting. We are learning that a
wide variety of evolutionary experiments, using bipedalism as a recurring
theme, took off about five million years ago. Most failed. One branching
lineage survived to the present. Also, our early ancestors were not poor
bipeds who evolved slowly into "good" two-legged walkers. Emerging evidence
suggests that a menagerie of species existed with a variety of
characteristics, and they did not form one linear progression from "primitive"
to "advanced" bipeds. Our obsession with linear progress has led us severely
astray in solving the riddle of why we became bipedal.
How we walk today comes from a cornucopia of evolutionary
forces at work on our ancestors" bodies. The modern architecture of the
spine, pelvis, feet, and hands, and even nervous and circulatory systems,
follows directly from the conversion from quadrupedalism to bipedalism. Other
changes, not preserved in stone but equally important in our ability to stand
and walk on two legs, took place in our behavior. Our apelike ancestors lived
in the forest, climbed in trees, and ate fruits and leaves and occasionally
meat. As the hominid emerged from the forest, it underwent changes in
foraging strategies, diet, preferred habitat, and tool technologies. The
hominid"s mating system and social life are unknown to us, although we can
make some reasonable inferences. And from this ape ancestor came one
with a cerebral volume that was only marginally larger but had an entirely new
way of walking. No doubt, changes in social behavior contributed to cognitive
changes. Tool technologies changed too, expanding the resources available
to this population. Because all these new aspects of emerging humanity
cascaded one upon the other, teasing out which caused which is difficult.
The intricate puzzle of our humanity came into focus as new pieces were
added to old ones, slowly changing our ancestors from one thing to another.
How we became bipedal is a chronicle of how we became human.
As our way of moving about changed, so did our niche in the world, our
perspective, and our prospects. This chronicle is also an argument for why
we must move our view of the earliest stages of humanity from old-fashioned
notions of progress and linearity into a more modern Darwinian sensibility.
The debates in human evolution research are fierce, because the fossils are
few and far between, and because their implications are far-reaching. I will try
to convey a sense of the science and the scientific politics that drive the
process of making and breaking theories, as well as recent research that has
uncovered a variety of key pieces of human ancestry. The story at the heart
of this book is truly an odyssey, made more fantastic because it actually
occurred.

Copyright © 2003 by Craig Stanford. Reprinted by permission of Houghton
Mifflin Company.