How do we know?
This is the story of how humans first evolved in Africa and then began a wave of migrations. These great migrations are the reason why humans are now occupying all parts of the world. But first, we must answer the question, how do we know about humanity’s past? There are two kinds of evidence described by the evolutionary biologist Richard Dawkins:
Fossils (bodies and bones) and Artifacts (ancient tools and art):
These are, says Dawkins, “hard relics dating back more than 10,000 years” or “imprints of these relics preserved in stone.” Fossils and artifacts can be dated using “relative dating.” Here the order in which fossils or artifacts are found in the ground is important. The higher up they are found, the more recent they must be. A more accurate and “absolute method” method for dating fossils uses radiometric methods. In this method scientists know the amount of a particular element and know how fast it decays. This allows them to date fossils from hundreds of years ago to millions of years ago.
DNA is a molecule that was first discovered in 1869 by the chemist Friedrich Miescher. It took nearly 100 years for the structure of DNA to be understood (by Francis Crick and James Watson) in the 1950s. The DNA molecule provides instructions for the reproduction and making of all life forms on earth. By finding out the sequence of atoms in DNA, molecular biologists can trace a life form’s ancestry back into the future.
The great migrations
Using the evidence of dated fossils and artifacts as well as DNA analysis, scientists have strong evidence that our ancient ancestors first evolved in present-day Ethiopia between 300,000 and 200,000 years ago. This population is estimated to have been small and at most 10,000 people.
We emerged from this small family of homo sapiens (the scientific name given to our human species). Due to competition from their fellow family members and the scarce resources, these people started moving away from their original home in search of more food and shelter. Major waves of these migrations “out-of-Africa” occurred from 270,000 to 215,000 years ago and from 130,000 to 115,000 years ago. The most recent and most significant migration took place around 70,000 to 50,000 years ago.
The DNA record shows that as homo sapiens migrated, they sometimes met other human-type species such as the Neanderthals, and they either killed these other species or intermarried.
It is incredible to envisage the long and dangerous trek our ancestors took – first into Asia and Europe and then over the Bering Straits from what is now Eastern Russia into Alaska and from there over thousands of years down the entire American continent. Our ancestors also made long sea voyages from Asia into Australia and Polynesia. We have been a species constantly on the move, exploring and searching for more resources, safety and opportunities.
We are one human
We often forget that DNA shows we humans are all almost identical. The differences are minuscule. Differences in skin and hair colour and in terms of height and weight. However, overwhelmingly we are the same and are one type of human.
Alan Morris of South Africa’s University of Cape Town says that before our ancestors’ migrations and before the world’s human population differentiated into the mishmash of races and ethnicities that exist today, “We were all Africans.”
Science journalists Lydia Ramsey Pflanzer and Samantha Lee write, “Our bodies have 3 billion genetic building blocks, or base pairs, that make us who we are. And of those 3 billion base pairs, only a tiny amount are unique to us, making us about 99.9% genetically similar to the next human. A recent TED talk by physicist and entrepreneur Riccardo Sabatini demonstrated that a printed version of your entire genetic code would occupy some 262,000 pages. Of those pages, just about 500 would be unique to us.”
All our differences are insignificant. We often hear boasts from one society or another claiming superiority over other people, but this is completely false. We are one family. Next time we are tempted to start an argument or fight over some trivial matter, we should pause and stop. We should remember that our common mothers and fathers made great migrations to all our present benefit.
One life force on earth
The commonality amongst humans is just an initial step. All life on earth originated from a common ancestor. The basic mechanism of life is the same across all life forms. 96% of our DNA is shared with chimpanzees but also 60% with a banana! We are cousins of all life on earth. With our evolved large brains, we have great advantages but also immense responsibilities to manage a peaceful world.