Walk or Roll?

How many steps do you take a day? Fitness experts say kids should take more than 12,000 to stay healthy. Sounds like a lot. Perhaps you'd rather bike or skate (also healthy choices). If you have a long way to go, Dad might drive you. A long time ago, people didn't have these choices, because they didn't have any wheels. In fact, a really long time ago, no one even walked on two legs.

Stand Up Straight!

Of all the millions of species of animals living on earth, none walks on two legs the way humans do. True, birds have only two legs, but their postures and bone structures are entirely different, and their primary means of moving is to fly. Over the centuries, human beings have developed a unique skeletal structure and the anatomy to walk and run upright. It is one of the things that makes us human.

Scientists disagree about when and why our early ancestors began to stand up straight. Did they first stand upright to see over tall grasses or to expose less of their bodies to the hot sun? Did walking upright make finding food easier? Could they run faster to escape predators? Whatever the reason, stand up they did.

Most scientists believe that humans evolved several million years ago in Africa from tree-climbing primates like the chimpanzee. Chimps, however, move along the ground by "knuckle walking," stopping occasionally to stand up straight and grab a tasty fruit or leaf. They can't stand or walk easily on two feet. But our human ancestors could. And as early humans walked upright more and more, their bodies gradually changed over millions of years. Their feet became arched to absorb shocks, bear more weight, and enable them to take long, striding steps. Their backbones developed a double curve to bring everything in line above their feet. Their skulls slowly changed shape to balance more comfortably on top of their spines. Their thighbones sloped inward and muscles grew stronger to help steady them as they placed their weight on one or the other foot between strides.

Standing on two legs had some additional benefits. It freed up their breathing, which may have enabled them to develop language. And it also freed up their hands. Then they made tools, built shelters, carried babies, and brought home more and better food, which helped their brains to grow larger. They began to look, act-and walk-like modern humans.

Where'd They Go?

Their bodies were getting bigger, too, and most large animals range farther in search of food than small ones. Where did the first walkers go, now that they could cover more ground more easily?

As the earth's climate changed over the years, early humans walked around Africa, over savannas and through forests, across rivers and hills. They camped and stayed in some places and then moved on when food became scarce. Generation after generation lived and walked like this, finally moving north and out of Africa. After 150,000 years, descendants of the first walkers made it into Asia. They walked into Europe, too, where they had to get used to the cold. Fossils tell us that early humans were living in Asia by about 1.8 million years ago, and in Europe about 800,000 years ago. Then, much later, perhaps around 12,000 years ago, humans walked into North America and spread all the way to the tip of South America.

Whew. That's a lot of walking. The wheel hadn't been invented. No one was riding horses yet. Early humans populated the world on their own two feet.

Living Barefoot

Much of that early walking was probably done barefoot. No one knows when the first shoes, probably sandals, were invented. But if you go outside barefoot a lot, you may notice that the bottoms of your feet get tough (and dirty) and you can walk almost anywhere without hurting them. People who walk barefoot all the time-and about a billion of them live on the planet today-develop a thick layer of keratin on the soles of their feet. This is the same material that hair, horns, and claws are made of. With their toughened soles, they can walk over rocks, thorns, and even hot coals (though not many people try this).

But tough soles can't protect you from everything. As our ancient ancestors walked, perhaps someone got tired of stubbing her toe, or maybe someone's feet got cold. People then began to make foot coverings of plant fiber or animal hide. These materials don't survive well through the years. The earliest pair of sandals that we know about is only 9,000 years old. Found in a cave in Utah, the sandals are woven of sagebrush bark and were well preserved by the dry climate. With a little mending, they would still be fashionable today.

On the Road

So, early humans walked everywhere, with or without shoes. There were no roads, of course, and certainly no sidewalks. But soon foot trails crisscrossed the land. The trails followed the paths of animals and they connected settlements. People carried trade goods back and forth across them. Shepherds herded their livestock along them. But before the wheel, how did people move huge loads? How did ancient people move massive stones to build pyramids, temples, and monuments?