The history of the planet Earth goes back as far as 4.5 billion years. However, human history covers a comparatively short span of Earth history, much less than 0.1%. However, human evolution is a complex story.
Mammals first appeared in the Triassic period (about 251 million years ago). After the extinction of dinosaurs about 66 million years ago, mammals began to flourish on the earth. Primates, a subset of mammals, evolved 59-40 million years ago in the forests of Africa. Part of them lived on the treetops, and the other part lived on the ground. Apes are tailless primates. They can divide into two; great apes (Hominidae) and lesser apes (Hylobatidae). Animals such as gorillas, chimpanzees, bonobos, and orangutans are among the great apes. Around 7-6 million years ago, human ancestors were divided genetically from their apelike relatives such as chimpanzees and bonobos.
The group of modern and extinct apes is also known as the hominid. Hominin (modern humans and their closest ancestors) can refer to as a subset of the hominid family. Early hominins used to live on treetops, but later they left the forest and began to live on the grasslands. Accordingly, they evolved to stand on their own two feet. Thus, they were able to see a vast area. It was helpful to survive against enemies. The other importance of standing on feet is that the other two limbs are free for different functions, such as making tools.
Evolution of Homo genus
As mentioned previously the homo genus genetically separated from chimpanzees like ancestors (Hominins species evolved into two groups, pan, and homo), 6 to 7 million years ago. Since then, several ancient human species have inhabited the earth such as Homo habilis, Homo erectus, and Homo sapiens. From those, all human species are now extinct except for modern humans. It is important to note that these species are not in a straight line of descent. For instance, Homo habilis did not evolve into Erectus, or Neanderthals did not evolve into Homo sapiens. Human evolution is not linear progress. In fact, most of these species lived simultaneously. Modern humans are descents of only one group of human species that have lived on the earth.
Leap from apes to homos
Humankind was very much in the middle-of-the-food chain from 5 – 6 million years until 100,000 years ago – and it wasn’t until then that they became top of the food chain. However, for other animals, it took millions of years to become the top of the food chain. Comparatively, humans took a much quick jump. As a result, humans are anxious and stressed because they aren’t used to being at the top of the food chain for a long time period.
Humans, on the other hand, have a larger brain than consumes 25% of their body’s energy. The invention of fire and the ability to prepare food paved the door for the development of a smaller intestine and a larger brain. Less energy is delivered to the limbs as more energy is utilized for the brain. As a result, compared to their ape-like siblings, humans have weaker legs and hands.
When and where did our species originate?
During the last two decades of the 20th century, there was a debate whether Homo sapiens originated from local ancestors across the globe or originated in a single region and then spread. Two major and opposing old opinions were known as the ‘Out of Africa’ model and the ‘Multiregional’ model.
Out of Africa model
The most widely accepted hypothesis for the origins of modern humans was the ‘Out of Africa’ model. According to this model, modern humans descended from a single group of ancestors in Africa within the last 200,000 years and they moved to the Middle East 100,000 years ago. The various physical characteristics that may currently be found in modern people from various geographical places throughout the world are thought to have evolved in the last few thousand years or so.
Modern humans replaced all other human species as they spread. The most extreme variant of this scenario proposed that modern humans would completely displace older humans, with no interbreeding. Interbreeding between these populations was allowed in less extreme forms. Homo heidelbergensis replaced the population in Africa and Europe, Homo erectus in Asia, and Homo neanderthalensis in Europe.
The Multiregional Model
The ‘Multiregional’ model suggests that early humans lived in a series of regional groups, rather than being isolated individuals. Hence, interbreeding between different regional populations did occur. That is why geographically separated populations remain similar to one another.
Recent findings – including new fossils and improved DNA research and dating techniques – confirm the complexity of modern human (Homo sapiens) origins. As similar to the out of Africa model Homo sapiens came from a population of Homo sapiens that spread out of Africa 60,000 years ago but interbred with local ancient populations as they did so. That is why Neanderthal and Denisovan genes are found in all living populations outside Africa.