By Mariano Tovar
If someone were to stand on a pulpit and say that all humans come from a first woman, Eve, and that this is an indisputable biblical truth, we would probably pay little or very little attention. But if a team of researchers were to publish in the prestigious scientific journal Nature that mitochondrial DNA proves that all of today’s humanity comes from a single woman, we would certainly not be so quick to dismiss it.
The findings are not even current. That famous article, “Mitochondrial DNA and human evolution” was published in 1987 and was the first study to uncover the family tree of human evolution. Moreover, it came to that puzzling conclusion: all human beings come from a single woman, who was quickly christened “Mitochondrial Eve”.
Inside every cell of the body there is an organelle called mitochondria that has a DNA distinct from that of the cell itself. It has 37 genes of its own and is descended solely from the mother’s mitochondrial DNA. Scientists sequenced that DNA in individuals from all over the world, analyzed their mutations, and came to the universally accepted conclusion that the original mitochondrial DNA came from a single individual, a woman. The study of the genetic mutations that this mitochondrial DNA has undergone has also served to understand human migrations throughout history.
Where did Mitochondrial Eve live?
Many studies have tried to place that first woman in time and on the map. And from what is known so far, she lived in southern Africa, in what is now Botswana, some 200,000 years ago. The problem is that the earliest evidence of Homo sapiens goes back 300,000 years, so before that woman there were many other women. How do we understand this?
The only scientific explanation is that all women with different mitochondrial DNA had their gene transmission interrupted because they only generated males or had no offspring at some point in history. It seems a little difficult to understand, but the theory of genetic drift 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. This is something that occurs randomly, without taking into account natural selection, mutations or any other external factor, which also have an influence in deciding the dominant sequence.
To make matters worse, the ‘Y’ chromosomes are inherited paternally, so using the same technique as with mitochondrial DNA, studies have been done to arrive at an original first man, who has been christened “Chromosonic Adam”. Many studies note a discrepancy of 50,000 years between the age of the original ‘Y’ chromosome and that of the mitochondrial DNA, but some others place them at a similar time. Adam and Eve, or whatever they were called, could have lived at similar times and in relatively close proximity. Whether they knew each other or not, they are the parents of all humans on the planet today… even if they lived surrounded by many other men and women like them.
