Human History Isn’t a Straight Line – It’s a Tangled Web

Human history is often shown as a neat March of Progress from one species to the next. Find out how DNA testing proves it’s much more complicated than that.

Our science textbook in school had a diagram that I’m sure readers will remember. On the left-hand side was a picture of a primitive ape.

From there, from left to right, the diagram showed a sequence of more and more human-like creatures. At the far right was the crowning glory of the process, the modern human. He was male and white, of course.

The famous image is called The March of Progress. A picture is worth a thousand words and this one made its point better than anything else could.

FAMOUS IMAGE CALLED THE MARCH OF PROGRESS

Human evolution is a proven scientific fact. Even so, the diagram doesn’t tell the whole story.

It implies that evolution went merrily along in a straight line with one creature smoothly turning into the next. That’s how people, including scientists, viewed evolution fifty years ago.

Nobody meant to deceive anybody, least of all impressionable school-kids. Even so, this assembly-line view of an organic process is simplistic.

MOST THOROUGH REVIEW OF HUMAN GENETIC DIVERSITY EVER

That got even clearer this week as the journal Science published a new study. It provides the most thorough review of human genetic diversity ever done.

As we’ve discussed in earlier stories, DNA technology has done more than screen for diseases and solve crimes, vital as those things are. It’s also shed light on human history.

A research team from the Wellcome Sanger Institute and the University of Cambridge sequenced 929 human genomes. They found a lot more variation than anybody knew about before. As well, the way our ancestors varied, moved around and mixed over the last 2.5 million years was complicated.

HOW OUR ANCESTORS MOVED AND MIXED WAS COMPLICATED

The standard model is that our human ancestors split off from Neanderthals and Denisovans about 500,000 years ago. What we call modern humans arose around 200,000 years ago in what we call the paleolithic period.

The ancestors of all homo sapiens came from Africa. Around 50,000 years ago, some of them started wandering out of Africa and mingling with groups in other parts of the world.

That’s when things get complicated. Everybody started mixing and moving around everywhere.

EVERYBODY STARTED MOVING AND MIXING EVERYWHERE

A big part of the reason was that around 10,000 years ago, a thousand years or so after the ice age started winding down, our ancestors went through the neolithic revolution. That’s when people moved away from hunting and gathering and gradually started their own food production.

To find out more about this complex era, the team used brand new, top quality gene sequencing tools to study the DNA from 929 people from 54 separate groups all over the world. It’s part of the Human Genome Diversity Project (HGDP) and it holds details we’ve never had access to before.

They found millions of newly discovered DNA variations that only show up in in one part of the world. They’re rare if you look at them globally but quite common in certain parts of Oceania and Africa.

MILLIONS OF NEWLY DISCOVERED DNA VARIATIONS

Up until now, scientists have mainly looked at DNA samples from people whose ancestors were European. That’s who was convenient to study but since most people aren’t European, it left out a lot of critical information.

This study changes that and it will have a lot of medical and other benefits for underrepresented populations. Team member Dr. Anders Bergstrom put it this way. “The detail provided by this study allows us to look deeper into human history, particularly inside Africa where less is currently known about the timescale of human evolution.”

They also found that even though there are all these new local genes, it’s not like everybody in those places had the gene and nobody had it anywhere else. Instead, we can find traces of just about any genetic variation wherever we look.

“GRADUAL AND COMPLEX PROCESSING IN THE LAST 250,000 YEARS”

Dr. Bergstrom explains, “We find that the ancestors of present-day populations diversified through a gradual and complex process mostly during the last 250,000 years, with large amounts of gene flow between these early lineages. But we also see evidence that small parts of human ancestries trace back to groups that diversified much earlier than this.”

That’s where our March of Progress notion falls apart. For example, I have some Neanderthal genes in my ancestry and most readers probably do as well.

This comes from an event where modern humans mingled with Neanderthals not long after they left Africa. On the other hand, people who live in East Asia and Oceania have Denisovan genes that seem to have come from a couple of prehistoric “mixers.”

SOME MODERN HUMANS MOVED BACK INTO AFRICA

Also, as we’ve talked about in earlier stories, we can find Neanderthal DNA in people from West Africa. That shows that some modern humans moved back into Africa from Eurasia after their ancestors met up with some other kinds of people there.

Traditionally, anthropologists pieced together our past by looking at fossils and artifacts like stone tools and weapons from early hominids. We’ll always need that technique but the Human Genome Diversity Project provides another, and often more complete, picture.

.Hélène Blanché, is the Head of the Biological Resource Centre at the Centre d’Etude du Polymorphisme Humain (CEPH) in Paris. She explains it this way.

“HELP US UNDERSTAND OUR SPECIES AND HOW WE HAVE EVOLVED”

“The Human Genome Diversity Project resource has facilitated many new discoveries about human history in the past two decades. It is exciting to see that with the latest genomic sequencing technology, these genomes will continue to help us understand our species and how we have evolved.”

This is only the beginning of how DNA can explain the descent of humanity. Every culture has a story about where humans came from. Today, we need a new, global, science-based story that everyone in the world can tell each another.

Dr. Chris Tyler-Smith, who just retired from the Wellcome Sanger Institute, explained, “Already we can glimpse several tantalizing insights into human history. It will be particularly important for better understanding human evolution in Africa, as well as facilitating medical research for the full diversity of human ancestries.”

We always have more to learn if we dare to know.

Learn more:

Wellcome Sanger Institute
Insights into human genetic variation and population history from 929 diverse genomes
Hunter-Gatherer Culture and Storytellers
Neanderthal DNA Leaves Winding Trail
Is the Birthplace of All Humans in the Kalahari?

One thought on “Human History Isn’t a Straight Line – It’s a Tangled Web

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.