Living Columns & Blogs

Linked by our mamas to Ice Age

You might think you don’t know much about the history of Earth’s climate. But dramatic climate change is reflected in your genes.

Here’s the story.

There’s a special type of DNA that flows only from mamas to children. It doesn’t get shuffled with papas in the process of reproduction, like most genes, and that leads to some interesting consequences when it comes to studying human history and climate.

The unshuffled DNA that comes from mothers is called mitochondrial-DNA. Being a simple soul, I just call it "mama-DNA."

Not everybody in the world has the exact same type of mama-DNA. That’s because from time to time a small mutation occurs. As a result of those rare events, people around the world have a total of about 25 different types of mama-DNA.

The earliest and oldest mama-DNA groups are from people native to Africa. That genetic fact fits well with archeological evidence that modern people first arose in Africa and spread from there to the Middle East and elsewhere over time.

African natives have what’s called L-type mama-DNA. (If geologists had named the groups, we would have used long and obscure names such as “Proterozoic” or “Glossopteris” for each one. Mercifully, genetic scientists just used letters of the alphabet for the different groups.)

Two early bands of people who left Africa had M and N mama-DNA that had branched off from the L’s. From there, the story gets complicated as many splits from the M’s and N’s lead to the diversity in mama-DNA we see around the world today.

Native Americans have mama-DNA in groups A, B, C, D and X. People in northeast Asia have just the same types. That fits with the archeological evidence that North America was originally peopled by immigrants who came from Siberia into Alaska.

The passage from Siberia was made easier because the Ice Age was in full swing at the time. A great deal of Earth’s water was locked up in glacial ice, so sea level was much lower, making a land passage possible for tribes moving from Siberia into North America. That’s just one link between climate history and our genes.

National Geographic is sponsoring a mama-DNA project in which you can participate for a small fee. Through that program I’ve learned that my mother, maternal grandmother and maternal great-grandmother, etc., are in group-H. That fits with genealogical information that shows we go back to American colonial history and, prior to that, England.

About half of native Europeans are H’s. Just like me, Barack Obama may well be an H, because his mother and his maternal grandmother were of European origin.

The H-group arose about 45,000 years ago in the Middle East. The H-clan spread into Europe, but around 15,000, when glaciers were at their maximum during the most bitter part of the Ice Age, we were pushed south into what’s now Spain, Italy and the Balkans. The world’s climate then changed once more, and Earth climbed out of the "deep freeze." We H-folks spread gradually north throughout Europe as the ice sheets retreated. First, we percolated up through France and Germany, then up the coast Norway and northward into the meadows of Sweden, our genes oozing north as the glaciers melted away.

Ultimately, of course, the H group goes back to the L-groups in Africa. Africa is the mother of us all, as both genetics and anthropology show us.

But back to climate and the fact that some of our genes have been pushed around by glaciers. It’s staggering – but ultimately uplifting – to think about the great climate changes that our ancestors faced. Considering they had only the most primitive stone, wood and bone technologies, they did well to survive, let alone take advantage of opportunity to walk across land bridges into new lands. And that makes me quite hopeful about our ultimate response to the next climate shift.

You can learn more about mama-DNA and take an armchair journey with all the peoples of the world back to the Ice Age by looking on the web at National Geographic’s “Genographic Project.”

Enjoy the trip.

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