What Makes Us 'Human'?
Are humans really biologically and socially different from the rest of the created world? Are there definitive characteristics that separate humans from other forms of life, or are humans simply an improvement on the body plans of other animals, the result of random processes that have occurred over millions of years?
There have been many attempts to answer these questions. Paleontologists have identified many features unique to human skeletons, enabling them to distinguish between human and ape (chimpanzees, gorillas, and orangutans) fossils.
For example, apes and man share the same tooth pattern in their jaws; two incisors, one canine, two premolars, and three molars. But the tooth-bearing mandible (jawbone) in humans is smaller in relation to the skull and V-shaped, while that of an ape is U-shaped.
Another skeletal feature, the human pelvis, is more bowl-shaped than that of an ape, providing support for the abdominal organs as a result of the constant upright position of humans. But these skeletal qualities can't fully define "what makes us human." They only describe some of the attributes of the "vessel" that "houses" a human.
Anthropologists have looked for cultural evidence to identify and describe human remains and help determine "what makes us human." Humans have been described as tool users, once thought to be a quality unique from all other animals. However, extensive studies over the years by many researchers has identified the tool use by chimpanzees, and more recently gorillas, indicating that use of crude tools is not necessarily a unique human feature. Even a sea otter uses a crude tool, such as a rock, to crack open shell fish. The use of fire and burying the dead are also cited as evidence of "what makes us human." It certainly could be argued that using fire and evidence of burials are unique to humans, but these activities result from the spiritual nature within humans. Fire use and religion (funerals) do not fully explain "what makes us human."
Currently, molecular geneticists have taken their turn at defining a human based on DNA sequence differences between humans and apes. The arrangement, sequence, and expression levels of our DNA will provide valuable information of what makes a human unique from other created kinds, including the skeletal features and behavioral differences mentioned above.
Part of what it means to be human is how we became human. Over a long period of time, as early humans adapted to a changing world, they evolved certain characteristics that help define our species today.
Walking Upright
Walking-One Step at a Time
The earliest humans climbed trees and walked on the ground. This flexibility helped them get around in diverse habitats and cope with changing climates.
From at least 6 to 3 million years ago, early humans combined apelike and humanlike ways of moving around. Fossil bones like the ones you see here record a gradual transition from climbing trees to walking upright on a regular basis.
7–6 million years ago
Sahelanthropus may have walked on two legs.
Becoming bipedal
By 6 million years ago
The oldest evidence for walking on two legs comes from one of the earliest humans known, Sahelanthropus. Walking upright may have helped this species survive in the diverse habitats near where it lived—including forests and grasslands.
Leg support
6 million years ago
The upper part of this thigh bone is similar in size to those of other large apes. But the angled part more closely resembles that of modern humans. It formed a strong bridge with the hip to support the body’s weight, suggesting Orrorin tugenensis walked upright.
Strong knee
4.1 million years ago
Every time you take a step, you briefly stand on one leg—putting stress on your leg bones. The wide area of bone just below this the knee joint in Australopithecus anamensis is a result of that stress. It provides strong evidence that this individual walked upright.
Mostly bipedal
By 4 million years ago
Fossils from around this time period come from early human species that lived near open areas and dense woods. Their bodies had evolved in ways that enabled them to walk upright most of the time, but still climb trees. As a result, they could take advantage of both habitats.
Curved spine
2.5 million years ago
The curve of your lower back absorbs shock when you walk. It is uniquely human. You can see a similar curve in the spine of this early human, Australopithecus africanus, who walked upright in a way very similar to modern humans.
Hip support
1.95 million years ago
The size and broad shape of the hip bones of Homo erectus are similar to a modern human’s, showing that this early human species had given up climbing for walking.
Fully bipedal
By 1.9 million years ago
The pelvis and thigh bones (outline to right) of Homo erectus are similar to modern humans, and show that this early human was able to walk long distances. That ability was a big advantage during this time period. East Africa’s environments were fluctuating widely between moist and dry, and open grasslands were beginning to spread.
Long leg
1.89 million years ago
The long thigh bones of Homo erectus enabled its owner to take long strides and therefore to walk farther and faster than earlier humans.
- Press your fingers beneath the top bones of both of your hips.
- Now stand on one leg at a time.
- Can you feel the muscles contract?
These are the muscles that support your body during walking. They attach to the areas that curve inward above the hip socket.
Tools & Foods
Early humans in East Africa used hammerstones to strike stone cores and produce sharp flakes. For more than 2 million years, early humans used these tools to cut, pound, crush, and access new foods—including meat from large animals.
Handaxes came in handy
Beginning 1.7 million years ago
Around this time, toolmakers began to strike huge flakes off stone cores. They shaped the large flakes into handaxes by striking smaller flakes all around the edges. These multipurpose tools dominated early human technology for more than a million years. Ancient handaxes have been found in Africa, Asia, and Europe.
Handaxe Makers Cope with Catastrophe
Smithsonian scientists and their Chinese colleagues found these handaxes in the same sediment layer with tektites, small rocks that formed during a meteor impact 803,000 years ago.
Since the handaxes and tektites were in the same layer, both are the same age. Early humans must have moved into the area right after the impact. They may have made the handaxes from rocks that were exposed when forests burned.
What’s cooking?
By 790,000 years ago
Control of fire provided a new tool with several uses—including cooking, which led to a fundamental change in the early human diet. Cooking released nutrients in foods and made them easier to digest. It also rid some plants of poisons.
The earliest hearths are at least 790,000 years old. Some researchers think cooking may reach back more than 1.5 million years.
Early humans butchered large animals as long as 2.6 million years ago. But they may have scavenged the kills from lions and other predators. The early humans who made this spear were hunting large animals, probably on a regular basis.
Reducing the risk
Hunting large animals was a risky business. Long spears like this one were thrust into an animal, enabling our ancestors to hunt from a somewhat safer distance than was possible with earlier weapons. Three wooden spears like the 400,000-year-old one illustrated here were found at Schöningen, Germany, along with stone tools and the butchered remains of more than 10 horses.
Explosion of technology
By 100,000 years ago
Eventually new kinds of tools replaced stone handaxes. Some were small or made of several parts. Some were made of bone, ivory, or antler. Over the past 100,000 years, as modern humans spread around the world, the pace of technological change accelerated—leading to today’s extraordinary diversity of specialized tools.
Carving and shaping
Burins are specialized stone flakes with sharp, chisel-like tips. Humans used them to work bone, antler, ivory, and wood and to carve designs and images on the surfaces of these materials.
Fishing
More than 70,000 years ago, humans in Central Africa used some of the earliest barbed points to spear huge prehistoric catfish weighing as much as 68 kg (150 lbs.), enough to feed 80 people for two days. Later, humans used harpoons to hunt large, fast marine mammals.
Hunting fast and dangerous prey
Spear-throwers provided leverage for hurling spears and darts greater distances with more speed and accuracy and with less chance of injury from prey. Stone or bone points, attached to spears or darts, enabled humans to exploit fast-moving prey like birds and large, dangerous prey like mammoths.
Storing things.
Early humans may have made bags from skin long ago. By around 26,000 years ago, they were weaving plant fibers to make cords and perhaps baskets. About 20,000 years ago, in China, they began making pottery.
Social Life
Group Survival
Sharing food, caring for infants, and building social networks helped our ancestors meet the daily challenges of their environments.
Over time, early humans began to gather at hearths and shelters to eat and socialize. As brains became larger and more complex, growing up took longer—requiring more parental care and the protective environment of a home. Expanding social networks led, eventually, to the complex social lives of modern humans.
Sharing resources
Beginning 2.6–1.8 million years ago
Some groups of early humans began collecting tools and food from a variety of places and bringing them to favored resting and eating spots. Sharing vital resources with other members of the group led to stronger social bonds and enhanced the group’s chances of survival.
More time to grow
Beginning 500,000–160,000 years ago
By this time, early humans had evolved much larger brains. Infants were born with small brains, enabling the head to pass through the birth canal. The brain continued to grow throughout a long childhood. During adolescence, youngsters continued to prepare for the challenges of adulthood.
Two Roads to Adulthood
Humans are unique among primates in having long, distinct periods of childhood and adolescence. These stages enable us to learn, play, socialize, and absorb important experiences prior to adulthood.
During childhood, human children depend on adults for food and care. During adolescence, a growth spurt occurs, and male and female body features develop.
Explore one of the Earliest-known Human Shelters
This 400,000-year-old shelter at Terra Amata, France, provided protection for an early human family or social group. Scientists found post holes and other evidence of multiple shelters at this site. Some shelters were as long as 14.9 m (49 ft.).
Scientists also found fossil human feces here. They contain pollen from plants that blossom in late spring and early summer, indicating when humans occupied the shelters.
Building Social Networks
Beginning 130,000 years ago
Over time, humans began interacting with social groups located far from their own. By 130,000 years ago, groups who lived 300 km (186 mi) apart were exchanging resources. Social networks continued to expand and become more complex. Today, people from around the globe rely on one another for information and goods.
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