Heva Mitochondrialis

MITOCHONDRIAL EVE

Amici, Americani, Compatrioatae,

As my siblings and my friends from the Pentecostal Church of my youth will recall, the apparent discrepancies between the scientific account of the origin of the universe and humankind, and the Biblical account of Creation bothered me a great deal as a teenager. When as an adult I became a Catholic and began unlocking the treasures of the Church over the past 2000 years – especially the early Church Fathers and all those Catholic clergy (like Father Georges LeMaitre) who were scientists – I came to discover that there is no conflict between real science and the teaching of Holy Mother Church found in Sacred Scripture, Sacred Tradition and Her Magisterium. This post is a continuation along that theme and I hope it (along with other recent posts) helps the reader (whether Catholic, Orthodox or Protestant) in seeing and understanding the essential unity of science and our Christian Faith.

The next Old Testament reading on Creation in the daily Divine Liturgy is Genesis 2:18-25, the account of the creation of Eve, wife of Adam and Mother of Humankind. This post will explain the scientific basis for the Genesis account. Much of what is provided below was prepared and delivered as an apologetics training course some 10 or so years ago.

In 1987, geneticists in the journal Nature examined the mitochondrial DNA (mtDNA) from 147 people across all major racial groups. These researchers found that the lineage of all people alive today falls on one of two branches in humanity's family tree. One of these branches consists of nothing but African lineage. The other contains all other groups, including some African lineage.

The geneticists concluded that every person on Earth can trace his or her lineage back to a single common female ancestor who lived around 200K years ago. Because one entire branch of human lineage is of African origin and the other contains African lineage as well, the study's authors concluded Africa is the place where this woman lived. The scientists named this common female ancestor Mitochondrial Eve.

Another geneticist, Dr. Wesley Brown, in 1980 noticed that when the mtDNA of two humans is compared, the samples are much more similar than when the mtDNA of two other primates -- for example, two chimpanzees -- is compared. Brown found, in fact, that the mtDNA of two humans has only about half as many differences as the mtDNA of two other primates within the same species. This suggests that humans share a much more recent common ancestor

Evolutionists maintain that the Mitochondrial Eve was not the first -- or only -- woman on Earth during the time she lived. Instead, this woman is simply the most recent person to whom all people can trace their genealogy. According to them, there were many women who came before her and many women who came after, but her life is the point from which all modern branches on humanity's family tree grew. If true, then why is she the only one to have successfully passed down her mtDNA?

When the researchers in the 1987 study looked at samples taken from 147 different people and fetuses, they found 133 distinct sequences of mtDNA. After comparing the number of differences among the mtDNA samples within races, they found that Africans have the most diversity (that is, the most number of differences) of any single racial group. This would suggest that the mtDNA found in Africans is the oldest. Since it has had the most mutations, a process which takes time, it must be the oldest of lineages around today.

The two distinct branches contained the mtDNA are found in the five main populations on the planet:

1. African
2. Asian
3. European
4. Australian
5. New Guinean

Researchers found that in the branch that was not exclusively African, racial populations often had more than one lineage. For example, one New Guinean lineage finds its closest relative in a lineage present in Asia, not New Guinea. All of the lineages and both of the two branches, however, can all be traced back to one theorized point: Mitochondrial Eve.

So how did Eve end up being humanity's most recent common ancestor? We shall investigate that, as well as some arguments lodged against the Mitochondrial Eve theory. But first, what is DNA, what are mitochondria, and why do scientists use mtDNA to track lineage?

Biologists have been aware of mitochondria since the 19th century. In the late 1970s the value of using the DNA within mitochondria to track ancient human history became clear. Mitochondrial DNA differs in a few key ways from nuclear DNA -- the variety of DNA located within the nucleus of each of one’s cells determines eye color, racial features, susceptibility to certain diseases and other defining characteristics. mtDNA, on the other hand, contains codes for making proteins and carrying out the other processes mitochondria undertake.

The genes carried in the form of nuclear DNA are the result of a merger between mother's and father's DNA -- this merger is called recombination. mtDNA, however, is derived almost exclusively from the mother. This is because the egg of a female human contains lots of mtDNA, while male sperm contains just a bit of mitochondria. A function of a single mitochondrion is generating power for the cell containing it, and sperm use a few mitochondria in the tail to power their race towards the egg for fertilization. These mitochondria are destroyed after the sperm fertilizes the egg, and thus any mtDNA that could be passed on from the father's side is lost.

This means that mtDNA is matrilineal -- only the mother's side survives from generation to generation. A mother who gives birth only to sons will see her mtDNA lineage lost. Examination of mtDNA so far has yielded only rare and unusual cases where paternal mtDNA survives and is passed onto the child. Mitochondria are also valuable to evolutionists because copies of the exact same mtDNA one has can be found in cells throughout one’s body. Within each cell, too, there may be thousands of copies of mtDNA. Conversely, the nuclear DNA in a cell usually contains just two copies. It is also easier to extract mtDNA than nuclear DNA, since it is found outside the fragile and more rapidly decaying nucleus of the cell.

What all this adds up to is that a one’s mtDNA is the same as one’s mother's, since there is no recombination to form a third version, distinct from both one’s mother's and father's but a combination of both. This makes mtDNA much easier to track from an anthropological standpoint. Humans have been around for a long time. In the hundreds of thousands of years we've been walking the planet, our numbers have grown. How is it that only about 200K years ago a single woman became the great-grandmother of us all? Does NOT human history go further back than that? In the following text we will see how humanity may have come close to extinction, setting the stage for Mitochondrial Eve to leave her enduring legacy.

It was estimated that Mitochondrial Eve lived about 200K years ago. With a margin of error included, she would have been alive between 500K and 50K years ago. Given that Eve is thought to have lived during a time when there were other women alive, how is it that all of us alive today descended from her alone? There are a couple explanations for how only Eve’s mtDNA alone could have survived. Most likely a combination of converging factors is responsible.

The likeliest possibility is that an evolutionary bottleneck occurred among humankind while Eve was alive. This is a situation where a large majority of the members of species suddenly die out, bringing the species to the verge of extinction. This sudden decrease in numbers is NOT due to any kind of failure to adapt. Instead, it's more likely the result of a catastrophe of some sort, for example, the result of a comet hitting the Earth or a super volcano eruption. Afterward, just a few members remain to repopulate the group and continue to evolve. Bottlenecks are suspected to have taken place at different times in humanity’s history Thus, it is credible that an event like this could have taken place during Eve’s lifetime.

A 1998 report concluded that about 70K years ago, humanity was reduced to only about 15K people on the whole planet. With very few people spread out across the planet, humankind was on the verge of extinction. The event that caused the near-loss of our species was an eruption of Mount Toba in Sumatra. This volcanic eruption was so immense that it lowered global temperatures, killed off the animals and plants that nourished humans, and spurred the coldest ice age the planet has seen, lasting 1,000 years.

The Mitochondrial Eve theory evokes similar scenarios. IF the human population was reduced dramatically, AND there were NOT many women around to bear children, THEN the stage is set for one “Lucky Mother” to emerge as a most recent common ancestor. It is possible that after a few generations, the mtDNA of the other women died out. IF a woman produces only male offspring, THEN her mtDNA will NOT be passed along, since children do NOT receive mtDNA from their father. This means that while the woman’s sons will have her mtDNA, her grandchildren will NOT, and her line will be lost. It is possible that this was the cause of Eve emerging as the sole “Lucky Mother” who in essence gave birth to us all.

Alternate Hypothesis - A reviewer of this presentation asked: Is it truly Eve we are talking about or is it not more likely that the "Lucky Woman" was Noah's wife? She fits the conditions described exactly...except the literal readers of the Bible would place her more in the 5,000 - 10,000 BC range. While the Bible states we have one common mother in Eve, the events that have occurred since then would seem to make it impossible to ascertain what she was like. Only Noah's wife, or the wives of his sons could be the focal point of our mtDNA since the Flood. And the Flood provides exactly the kind of cataclysmic event that would have created a bottleneck as described in your presentation.

My answer to this alternate hypothesis is as follows: For mtDNA to be common in all humans, both Noah’s wife and the wives of Noah’s sons must have had common mtDNA. Given that the wives of Noah’s three sons were from parents other than Noah and Noah’s wife, this means the common mtDNA must have originated with a primordial Eve.

Although talk of genetic mutations and DNA sequences makes it seem complex, at its core, tracking mtDNA is based on a deceptively simple notion: People whose ancestors were once closely related should have almost identical mtDNA. mtDNA can undergo mutations over time, but it takes time for these mutations to occur. Logically, the fewer there are, the less time has gone by since two families' ancestors diverged. Those people who have just a few differences in their mtDNA sequences would be more recently related than those sequences which bear many differences.

Let us suppose your great-great-grandmother on your mom's side -- whom we'll call Mildred -- had a sister, whom we'll call Tillie. Both shared identical mtDNA which they received from their mother. But imagine that Tillie and Mildred had a terrible argument, and Tillie moved across the country, while Mildred's descendants -- including you -- stayed put. Tillie and Millie never spoke again. Both women gave birth to girls, and so their matrilineal mtDNA was passed on. But as the generations continued, the families of the two grew less and less aware of the existence of the other branch, until neither line was aware of the other. But the two lines are about to be inadvertently reunited. Researchers placed a national advertisement asking for test subjects for a study of recent human population trends using mtDNA for mapping. By coincidence, you and a distant cousin of yours on Tillie's side of the family both decide to volunteer.

After they collect a DNA sample from you, the researchers compare your mtDNA to the sequences from the other candidates. Lo and behold -- they find that two volunteers are cousins. Comparing your mtDNA to your cousin's, the geneticists should be able to tell about how long ago Tillie and Mildred had their argument. If they checked the local populations of your area and your cousin's area, they should also be able to tell whether it was Tillie or Millie who migrated, by finding which population shared more of the mtDNA present in your family line. More people with the same mtDNA means that that sequence has been around longer. What's more, they can also conclude that since you and your cousin share similar mtDNA, you have a most common recent ancestor, the woman who is mother to Tillie and Mildred.

Since it takes a while for mtDNA mutations to occur, it would be pretty difficult for these imagined geneticists to pin down you and your cousin with accuracy. But when this technique is extrapolated over a period spanning tens or hundreds of thousands of years, it becomes much more viable. Not everyone accepts the Mitochondrial Eve theory, however.

Evolutionary mapping through the use of mtDNA is inexact. As mtDNA study continued after the late 1970s, scientists discovered a property known as heteroplasmy -- the presence of more than one sequence of mtDNA found in the same person. Even within a single person, there are differences between mtDNA that make comparing one person or group to another tricky. The 1987 study of the Mitochondrial Eve came under attack when it was pointed out that the "African" population the researchers sampled was actually made up almost entirely of African-Americans. Is it possible that in the few hundred years since Africans had been imported to the Americas against their will that African-Americans' mtDNA had mutated enough so as to render the sample useless? In the face of the criticism, researchers took an additional sample of Africans living in Africa, but found virtually the same results.

Another problem with mtDNA study is the differences in the rate of mutation. If a particular sequence of mtDNA was concluded to develop a mutation in 1,000 years, then would two strains of mtDNA from the same lineage with two mutations have diverged about 2,000 years ago? This is how researchers decided Mitochondrial Eve was living around 200,000 years ago. The researchers assumed that mtDNA mutates at a consistent rate. However, the rate of mutation for mtDNA is uncertain and immeasurable. If we look at the rate of mutation among a whole group of organisms, say, all people alive today -- called the phylogenetic rate -- we might conclude that mtDNA mutates at a consistent rate. But if we look at a single family line within that larger group -- the pedigree rate – we will most likely find an entirely different rate of mutation.

Since the "mutational clock" used by the researchers was called into question, they expanded the date for Eve's existence to between 500,000 and 50,000 years ago. Decades after the Mitochondrial Eve study was published, the results are still hotly debated. Are we all descended from a most recent common ancestor who lived 200,000 years ago? Can mtDNA even tell us precisely? These questions remain unanswered by science and frame the future work of evolutionary geneticists. But the 1987 study changed the way we think about ourselves as humans. It pointed out that somewhere down the line of history, we are all related.

Genesis chapter2: The LORD God formed man out of the clay of the ground and blew into his nostrils the breath of life, and so man became a living being. Then the LORD God planted a garden in Eden, in the east, and he placed there the man whom he had formed. …The LORD God then took the man and settled him in the garden of Eden, to cultivate and care for it. The LORD God gave man this order: "You are free to eat from any of the trees of the garden except the tree of knowledge of good and bad. From that tree you shall not eat; the moment you eat from it you are surely doomed to die." The LORD God said: "It is not good for the man to be alone. I will make a suitable partner for him." …So the LORD God cast a deep sleep on the man, and while he was asleep, he took out one of his ribs and closed up its place with flesh. The LORD God then built up into a woman the rib that he had taken from the man. When he brought her to the man, the man said: "This one, at last, is bone of my bones and flesh of my flesh; This one shall be called 'woman,' for out of 'her man' this one has been taken."

Pope Pius XII stated: "When, however, there is question of another conjectural opinion, namely polygenism, the children of the Church by no means enjoy such liberty. For the faithful cannot embrace that opinion which maintains either that after Adam there existed on this earth true men who did not take their origin through natural generation from him as from the first parents of all, or that Adam represents a certain number of first parents. Now, it is in no way apparent how such an opinion can be reconciled with that which the sources of revealed truth and the documents of the teaching authority of the Church proposed with regard to original sin which proceeds from a sin actually committed by an individual Adam, and which, through generation, is passed onto all and is in everyone as his own" (Humani Generis 37).

The story of the creation and fall of man is a true one, even if not written entirely according to modern literary techniques. The Catechism states: "The account of the fall in Genesis 3 uses figurative language, but affirms a primeval event, a deed that took place at the beginning of the history of man. Revelation gives us the certainty of faith that the whole of human history is marked by the original fault freely committed by our first parents" (CCC 390). Conclusion: If there is no Fall, then there is no Redemption.