The theory of the one common ancestor for all of humanity is as old as time, usually told as the bible story Adam and Eve, but years ago a group of researchers found conclusive evidence that the entirety of mitochondrial DNA in the world comes form a sole person, a woman that the scientist dubbed “Mitochondrial Eve”.
The story begins much earlier that when the original study that demonstrated this theory was published, but for the sake of simplicity, we will set the date to 1987 when the now renowned article “Mitochondrial DNA and human evolution” was published. This study was considered one of the biggest breakthroughs at the time as it was the first study to uncover the family tree of human evolution and reach the conclusion that we all come form a single source, the woman called “Mitochondrial Eve”.
Why is this so important? Surely this is kind of the same debate as the “who came first, the chicken or the egg?”. Well, it is important because this is the essence of who we are as a species. The mitochondria is the powerhouse of the human cell, it has different DNA than even cells and it directly descends from the mother’s mitochondrial DNA. Its 37 genes are completely unique and unrelated to any other part of the body.
When scientists began their study, they sequenced DNA from individuals that came from all over the world, and they discovered that the original mitochondrial DNA came from a single individual, which considering the matrilineal way of inheriting this DNA had to come from a woman. This conclusion led to some other even more fascinating discoveries, like the understanding of human migrations throughout history.
So, if we all come from the same woman, where do we come from?
That question is a lot harder to answer. There is a lot of conflicting evidence that make the first woman hard to place on a map. The most accepted theory is that she came from the African continent, more specifically the southern part, and the most agreed upon place seems to be present day Botswana. The timeline is what is causing more of an issue, as according to the calculations, this first woman was born around 200,000 years ago, but the earliest evidence of Homo sapiens goes back 300,000 years
This would mean that, before her, there were plenty of other women that could have been the origin of the human race as we know it, but that seems to contradict the findings.
There is one theory that seems to be quite universally accepted but still has a few question marks in it. That is that every other woman with different mitochondrial DNA was eliminated from the mitochondrial gene pool when they only had males or had no children. While this seems almost impossible nowadays, we must bear in mind that the mid boggling number of humans that exist today was not present even a thousand years ago, so this might be a lot more possible than we might think.
This is backed by the theory of genetic drift, which explains that “in small populations of any species with different versions of a DNA sequence, the less frequent versions tend to disappear and the majority one ends up becoming fixed in 100% of the population after a series of generations.”
Complicating things further, Y chromosomes are passed down exclusively through the paternal line, which has allowed researchers to apply a method similar to that used in mitochondrial DNA studies to trace back to a theoretical common male ancestor, often referred to as “Chromosomal Adam.” While some genetic analyses suggest a gap of roughly 50,000 years between this ancestor and the so-called “Mitochondrial Eve,” others argue they may have existed around the same period.
It is possible they lived in overlapping regions, though there is no way of knowing if they ever crossed paths. What is clear, however, is that these two individuals, among a much larger population, represent the most recent common ancestors along the male and female genetic lines for everyone alive today.