Around 200,000 years back, Sapiens evolved in Africa. Then around 60,000 years back they left East Africa towards the Arabian Peninsula and from there to India following, maybe a coastal route. This is what the Out of Africa theory says. When these sapiens reached Europe, they met other species such as Neanderthals and Denisovans and interbred with them. The other species died out and now we are the only homo species that remain. At least, that’s what we believed so far.
There not even a slender certainty that it is true. Sapien remains have been found at multiple sites in China that have been dated to between 70,000 and 120,000 years ago. Additional finds indicate that modern humans reached Southeast Asia and Australia prior to 60,000 years ago. This predates the time span normally attributed to the Out of Africa theory, implying that there were previous migrations from 120,000 years back. Here is the interesting data point: all of us — all non-Africans — are descendants of a single ancestral population dating back to 60, 000 years. This implies that the migrations prior to 60, 000 years, was probably a tiny population. Even though they were not that large, they left markers around the world for us to discover. Later a major migration occurred, leading to all of us.
It’s fancy to believe in a simple West to East migration in a linear time frame. Unfortunately, nature behaves differently. Human migration requires complicated models.
The second interesting data point comes from a discovery from a butchered rhino at Kalinga in the Philippines. The bone bed where this rhino met its grim death had 57 stone tools and was dated to between 777 – 631 thousand years before present. This pushes the date of appearance of hominins in the Philippines by hundreds of thousands of years. It is a big discovery. Of course, these were not sapiens, but Homo erectus. It seems there were no land bridges to the Philippines during that time and the only way these hominins could have reached there would have been by deliberately constructing rafts. Think about it, around 700, 000 years, our ancestors built rafts and crossed channels that were 10 KM wide.
We homo sapiens are the only surviving humans around. In fact, it has been that way for the last 10,000 years. We tend to forget that at some point, there were many types of humans (of genus Homo) on earth like the Homo neanderthalensis (Neanderthals), Homo soloensis, Homo floresiensis, Homo erectus, and Homo denisova (Denisovans). While the Neanderthals are the most famous among all of these, sapiens co-existed with the others and intermingled with them. We may even have caused their extinction
While all of us have some Neanderthal ancestry (1 – 4%), some of us (Australians, Indians) have more Denisovan ancestry (5%). This intermingling happened much after the Neanderthal mixture. This happened because all these three — sapiens, Neanderthals and Denisovans — were not different species, but of the same species. They produced offsprings together.
A new paper analyzed the amount of Denisovan ancestry and found that Indians have the largest admixture after the people in Australia. Among the Indians, the largest were among people in the Himalayan region and South and Central India. What is not known is this: Was there a single introgression of Denisovans into sapiens and it got diluted in various rates among the populations of the world or there were three different introgressions.
Looking at this paper, Sunil Deepak asks an interesting question.