Homo sapiens is part of a group called hominids, which were the earliest humanlike creatures. Based on archaeological and anthropological evidence, we think that hominids diverged from other primates somewhere between 2.5 and 4 million years ago in eastern and southern Africa. Though there was a degree of diversity among the hominid family, they all shared the trait of bipedalism, or the ability to walk upright on two legs.
Scientists have several theories about why early hominids evolved. One, the aridity hypothesis, suggests that early hominids were more suited to dry climates and evolved as the Africa’s dry savannah regions expanded.
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According to the savannah hypothesis, early tree-dwelling hominids may have been pushed out of their homes as environmental changes caused the forest regions to shrink and the size of the savannah expand. These changes, according to the savannah hypothesis, may have caused them to adapt to living on the ground and walking upright instead of climbing.
Hominids continued to evolve and develop unique characteristics. Their brain capacities increased, and approximately 2.3 million years ago, a hominid known as Homo habilis began to make and use simple tools. By a million years ago, some hominid species, particularly Homo erectus, began to migrate out of Africa and into Eurasia, where they began to make other advances like controlling fire.
Though there were once many kinds of hominids, only one remains: Homo sapiens. Extinction is a normal part of evolution, and scientists continue to theorize why other hominid species didn’t survive. We do have some clues as to why some species were less successful at surviving than others, such as an inability to cope with competition for food, changes in climate, and volcanic eruptions. ^44start superscript, 4, end superscript
Between 70,000 and 100,000 years ago, Homo sapiens began migrating from the African continent and populating parts of Europe and Asia. They reached the Australian continent in canoes sometime between 35,000 and 65,000 years ago.
Scientists studying land masses and climate know that the Pleistocene Ice Age created a land bridge that connected Asia and North America (Alaska) over 13,000 years ago. A widely accepted migration theory is that people crossed this land bridge and eventually migrated into North and South America. ^66start superscript, 6, end superscript
How were our ancestors able to achieve this feat, and why did they make the decision to leave their homes? The development of language around 50,000 years ago allowed people to make plans, solve problems, and organize effectively. We can’t be sure of the exact reasons humans first migrated off of the African continent, but it was likely correlated with a depletion of resources (like food) in their regions and competition for those resources. Once humans were able to communicate these concerns and make plans, they could assess together whether the pressures in their current home outweighed the risk of leaving to find a new one.
Map of the world showing the spread of Homo sapiens throughout the Earth over time. Homo sapiens are reflected with red arrows (shown populating the entire world over time), Homo neanderthalensis is reflected in orange in what is Europe and the Middle East today, and Homo erectus is represented in yellow in Africa, South Asia, and Southeast Asia.
When humans migrated from Africa to colder climates, they made clothing out of animal skins and constructed fires to keep themselves warm; often, they burned fires continuously through the winter. Sophisticated weapons, such as spears and bows and arrows, allowed them to kill large mammals efficiently. Along with changing climates, these hunting methods contributed to the extinction of giant land mammals such as mammoths, giant kangaroos, and mastodons. Fewer giant mammals, in turn, limited hunters’ available prey.
In addition to hunting animals and killing them out of self-defense, humans began to use the earth’s resources in new ways when they constructed semi-permanent settlements. Humans started shifting from nomadic lifestyles to fixed homes, using the natural resources there. Semi-permanent settlements would be the building-blocks of established communities and the development of agricultural practices.
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