Who We Are and How We Got Here summary

So, 50,000 years ago, the ancestors of modern non-African humans started to migrate out of their original continent. On their journeys, they encountered other species of humans descended from Homo erectus, including Neanderthals. But, within 10,000 years, they had proved so dominant that they were the only human species left.

Neanderthals are an interesting bunch. As a species, they were physically quite distinct from modern humans due to their large frames and projecting brows. Those features partly explain why they have a reputation for being “primitive.” But archeological finds demonstrate they were just as sharp as modern humans’ ancestors.

If you compare people from Europe, the Near East and parts of Central Asia, you’ll see that genetically speaking they have an extraordinary amount in common. But look at DNA from between 10,000 and 4,000 years ago, and it’s possible to deduce that there were at least four major populations throughout this area. And each one of these was as distant from each other as modern Europeans and East Asians.

This begs the question: what happened?

The Rig Veda, a foundational Hindu text that’s about 3,000 to 4,000 years old, relates how the warrior god Indra destroyed his enemies’ fortresses and established a new land for his chosen people, the Arya. Fortress remains in the Indus Valley in northern India can be dated to this period. So does this mean there is some truth to the legend?

Today, there are two main branches of languages in India, Indo-Aryan in the north and Dravidian in the south. A 2007 DNA study showed that all Indians are a mix of two ancient populations, one called Ancestral North Indians (ANI), who were related to Western Eurasians, and the other Ancestral South Indians (ASI), who aren't related to any populations outside of India.

Looking at genetics also gives us some idea about where Native Americans originated from.

In 2012, the author conducted a study that determined that all Native Americans from Central America southward were descended from a single population, which he named the “First Americans.” Supposedly they migrated to America sometime after 15,000 years ago.

Humans have made East Asia – China, Japan and Southeast Asia – their home for at least 1.7 million years. We know that because that’s the age of the oldest Homo erectus skeleton found in China. As the country still holds one-third of the world’s population today, we can be sure that an awful lot of migration has occurred in the intervening years.

The author’s laboratory has conducted studies which show that there are three main East Asian populations, descending from two ancient lines: the Yangtze River Ghost Population and the Yellow River Ghost Population.

Sometimes, people make the mistake of presuming that the migration that took modern non-Africans out of Africa 50,000 years ago was the last population movement that happened on the continent.

But this is far from the truth. There have been four major expansive migrations in Africa in just the last few thousand years.

The 1973 sci-fi novel Race Against Time is based on an interesting conjecture. It suggests that by the year 2300, humans would have turned into one “standard” population, losing biological diversity in the process.

There’s a problem with the premise, however. It’s built on the idea that population mixing that took place over the last few centuries is unique in human history. Genome analysis shows the truth of the matter: diverse populations have always bred with each other, simply as a result of frequent population movements. In practice, that sometimes meant couplings of powerful men with women from less powerful populations.

Back in 2006, the author was studying the genomes of African-American men. He was trying to work out why prostate cancer occurs 1.7 times more often among that group that among Americans of European ancestry.

His lab identified one part of the genome which contained at least seven factors that raised the risk of prostate cancer.