Mitochondrial Eve

Transcript

On January 1, 1987, a paper was published in the journal Nature which rocked the world of anthropology.

Researchers Allan Wilson, Mark Stoneking, and Rebecca Cann used the then-new science of genetic analysis to analyze the DNA in human mitochondria.

What they found was evidence that humans on Earth can trace their ancestry back to a single woman who lived approximately 180,000 years ago.

Learn more about Mitochondrial Eve, the mother of everyone, on this episode of Everything Everywhere Daily.

To start, we need a bit of background on how human genetics works.

Most of your genes are some combination of your mother and your father. What genes came from who can differ, so even siblings or fraternal twins can look very different, even though they have the same parents.

This mixing of genes is why sexual reproduction is so successful as an evolutionary strategy.

However, not all genes can be combined in such a manner. The mitochondria, which are the energy-producing center of our cells, have DNA that only comes from our mother.

That means that me, you, and everyone in the world will have that particular bit of DNA in common with our mothers. It isn’t something that is recombined with DNA from our fathers.

That means that the DNA in our mitochondria doesn’t change very much over time because it isn’t recombining during the process of reproduction.

However, it does change a little bit over time. These are mutations that occur naturally.

These mutations, statistically, occur at regular intervals. By determining the rate of mutation, you can create a type of Molecular clock and work backward to determine how long it was since different DNA diverged from the same DNA.

It was using this technique that the researchers determined how far back it was since we had our last common female ancestor.

What they determined is that it was a woman who lived about 180,000 years ago, give or take a few tens of thousands of years, and she lived in Africa.

She was dubbed Mitochondrial Eve.

There is one other thing we know about her. She must have had at least two daughters. Why? Because if she had zero, she couldn’t have passed along her mitochondrial DNA. If she had one, then that daughter would be our Mitochondrial Eve.

This technique has lead to some surprising conclusions and overturned many other theories in anthropology.

First, it lent a great deal of credibility to the “Out of Africa” hypothesis. This theory holds that humans developed in a single place in African and then left Africa in one or more migrations to populate the rest of the world, within the last 200,000 years or so.

This is the dominant theory today and it is supported by most evidence, especially genetic evidence.

Prior to the use of genetic evidence, the multiregional hypothesis had many adherents. This held that humans had a common ancestor about 2,000,000 years ago, they then spread around the world and evolved separately.

Secondly, it helped narrow down exactly where in Africa Mitochondrial Eve might have come from. Based on an analysis of the genes of current human populations, and based on 3,000-year-old remains, it is believed that Eve came from the region of what is today the Kalahari Desert in Southern Africa.

The term “Eve” obviously comes from the bible, and as such, there is some confusion over what the term Mitochondrial Eve means.

Mitochondrial Eve was not the first human or the first woman. She also wasn’t the only woman when she was alive. Other women alive when she was simply didn’t have female descendants who made it to today.

She is simply just the most recent common female ancestor that every human on Earth has today.

Moreover, and this is what really confuses many people, Mitochondrial Eve can change over time. As I just said, Mitochondrial Eve is defined to be the most recent female ancestor we all have in common, who we can identify via our mitochondrial DNA.

Over time, with increases in populations, people moving, and intermarrying, genetic populations become mixed and that person who is the most recent ancestor can change….but the fact still remains that we would still have a single recent ancestor which shares our mitochondrial DNA.

As I mentioned, only females can transmit mitochondrial DNA.

You might be wondering if there is an equivalent ancestor for males?

The answer is…..yes.

The male equivalent would be DNA passed in the Y chromosome. This is only passed from males to other males.

So, is there a Y Chromosome Adam who is the counterpart of the Mitochronial Eve?

Again, yes. However, Y Chromosome Adam and Mitochondrial Eve were not hanging out in some genetic Garden of Eden. In fact, they didn’t even live remotely close to each other.

It is estimated that Y Chromosome Adam may have existed about 60,000 years ago, as opposed to Mitochondrial Eve who existed 180,000 years ago.

How is this possible? Shouldn’t they have been at least somewhat contemporary?

Well, no. It all has to do with reproductive potential.

Not even factoring in children surviving to adulthood, there is a limit to the number of children a woman can have in her lifetime. For example, an 18th-century Russian woman holds the known record for having given birth 27 times in her life, with several multiple births.

However, there are many examples of chiefs, kings, and emperors who have fathered hundreds of children.

Ghengis Khan, who lived only 800 years ago, may have fathered thousands of children. Genetic testing has shown that 8% of all men living in the former Mongol Empire are direct descendants of Ghengis Khan, which means that at least 1% of everyone in the world today is descended from this one man who only lived centuries ago.

These super fathers are why there is such a time difference between our genetic Adam’s and Eve’s.

And just like our Mitochrondial Eve might change, so too will our Y Chromosome Adam. In fact, in the future, it might very well become Ghengis Khan.

To top it all off, I’ve been very specific when talking about both of these genetic ancestors. I’ve only discussed the specific origins of specific DNA. That doesn’t mean that these are our most common recent ancestors.

If you do the math, the number of ancestors we have doubles every generation. You have 2 parents, 4 grandparents, 8 great-grandparents, etc.

Assuming you have 25 years between generations on average, you quickly get to a point where we have billions of ancestors, which is much larger than the number of humans which existed.

That means the most recent common ancestor might have existed only about 3,000 to 5,000 years ago. This person might have been male or female, and statistically would have probably lived in southern or eastern Asia.

It is hard to track this person genetically because as I mentioned above, genes get mixed, and we can’t track this as well as we can with mitochondrial DNA and Y chromosomes, which are only passed by a single sex.

The thing which really lowered the date for this most recent common ancestor was the expansion of Europeans to places like the Americas, Australia, and the Pacific several hundred years ago.

So, when you hear someone say that all of humanity is one family, it isn’t just some crunchy, granola, kumbaya slogan. It is a literal truth.

All of us, you, me, and everyone listening to my words are all very distant cousins of each other.

—————————-

Executive Producer of Everything Everywhere Daily is James Mackala.

The associate producer is Thor Thomsen.

Today’s five-star reviews come from Podcast Republic listener Matthew who writes:

Interesting, ecclectic…I love it.

Thanks, Matthew. I’ll take it!

Thanks to everyone who has left reviews, and who have shared the podcast with their friends. Let’s face it, you all have at least one nerdy friend who would love this type of show. Share it with them and spread the nerd.