Can someone please explain the Mitochondrial Eve to me simply?

<whew!> There is so much fiction in what you were told or happened upon. Anyone that believes that I am tempted to sell them land in Florida dirt cheap, they can get on it twice a day when the tide is low and they better go with a good gator gun. Adam was first, then Eve from him, they existed in the same time frame. Think why women are more beautiful, they were made from flesh while man was made from dust. I could go into the proper order of things, but it might take ,longer than you were looking for.

I’ll take a stab at starting this.

First, the use of names like “Eve” and “Adam” are probably what makes it hard for people to wrap their minds around these ideas. I really wish they wouldn’t do this. Mitochondrial Eve has nothing to do with the biblical Eve. She was not even the first human woman.

What you need to understand first is what mitochondrial DNA is. Some gross generalizations will follow, just to keep this under 40 pages long.

Inside each of our cells is a nucleus. In that nucleus is DNA. That DNA is what determines how we are made. It determines what colour your eyes are and how tall you are… things like that. But also within our cells are things called mitochondria. These are the power centres of the cell. They make energy so that we can do everything that we do. Mitochondria resemble bacteria more than anything else. They are fundamentally very, very different from all other types of cell in the human body. Similarly, in plant cells, chloroplasts are the power centres, and they also resemble bacteria.

It took a long time to figure out a way for such a thing to have occurred – how could we have bacteria-like cells within our own cells, that function so differently from the way our own cells function? The current theory is that it is a kind of symbiosis – the cell of a very (VERY) early ancestor engulfed a bacteria-like cell, and they each provided the other with something important, such that they thrived better together than either one did apart. We see this in organisms like lichen – a lichen is algae + fungus that work together to thrive.

Ok, our cells contain these bacteria-like cells, mitochondria. Just like bacteria, they contain their own type of DNA, that determines the characteristics of the mitochondria. This DNA is not like the DNA in our nucleus, it is totally separate. Bacteria reproduce asexually, by making perfect clones of each other, and so do mitochondria. So, when more mitochondria are produced in our bodies, they look exactly alike, and they all contain DNA that is exactly alike.

The key – - – - – > Humans reproduce sexually (duh). In terms of our DNA, this means that our offspring receive a cocktail of DNA that is a mixture of the mother’s and the father’s DNA. It is totally unique to the offspring. BUT! The mitochondria of the offspring are ALL inherited from the mother. Think about how big a human egg is, compared with a tiny sperm. Pretty much all that sperm is made of is human DNA and a tail to make it move. But the egg contains a lot of cell material, including mitochondrial DNA. Thus, you received your first mitochondria from your mother, and she received her first mitochondria from her mother. And so on and so on. Not the same individual mitochondria – but they reproduce clonally, so they are indistinguishable from each other.

Well, mostly indistinguishable. There will be, over time, random mutations in the production of new mitochondria (just like there are random mutations in bacteria, that allow them to evolve to be resistant to antibiotics). The rate of mutation is something that we can quantify. Using that rate, and working with samples collected from people of different ethnicity, scientists estimated how long ago the first mitochondria that were enough like ours to have produced our mitochondria over as many generations were inherited. The woman who passed them on is Mitochondrial Eve.

The limitation of this question is that it doesn’t seek to find all the women who were Mitochondrial Eve’s contemporaries, but who didn’t contribute to this line. There would have been many thousands of women alive at the same time (just as there were also many thousands of men) – but we all descended from this one woman, and she was the most recent common ancestor.

You can see how arbitrary a “first” this is… we are sourcing the mitochondrial DNA of the most recent matrilineal common ancestor. This was not the first human, nor was it the most recent common ancestor (who was probably male, as you mention in your details). This explains why Mitochondrial Eve’s mother was not Mitochondrial Eve, nor her mother – because we’re looking for the most recent common ancestor here.

Small-scale analogy – - – - – - > Think of your own family. If you have siblings, then you and your siblings share many “matrilineal common ancestors”: your mother, your grandmother, your great-grandmother, etc. The most recent one is your mother.

Now if you include your cousins in that group, and find your most recent matrilineal common ancestor, you have to go up a generation. Your mother isn’t a common ancestor for both your siblings and your cousins.

Each time you widen the pool of people, you have to go further and further back to find the most recent matrilineal common ancestor. That’s what this is all about.

@dappled_leaves
Thanks for the detailed answer!
Yeaaa I should have clarified .. When I use the term “mitochondrial Eve” it’s certainly NOT meant to implicate any biblical context.. I thought perhaps the tags would be enough to explain that.. Lol and no, I was never under the impression there was one human at any given time.. I guess I should have explained myself better! Lol first time using this site.

Well thanks! Okay so I think I see where I went wrong.. And I think you’re right. The term “first” and “Eve” really are mis leading. When really as you said.. It’s “common” ancestor .. Not the “first” .. Right? And okay, so.. Whom did our most common mitochondrial ancestor mate with? If the earliest Y-chromosomal adam was 140,000 years apart.. Does that mean we just simply haven’t been able to trace him back far enough? Or is he something different all together?

@LiLithh13 “Whom did our most common mitochondrial ancestor mate with?”

Well, she could have had her pick! There were at least tens of thousands of humans around during her time, so there were lots of males. In a way, that’s not an important question, because the matrilineal line tells us the answer to this particular question about our shared mitochondrial DNA. That male didn’t contribute any mitochondrial DNA to us.

But you’re right, he definitely wasn’t Y-chromosomal Adam. That Adam is the result of a similar effort to find out how long ago the most recent common male ancestor lived. Again, it’s a pretty arbitrary benchmark. He would not have been the first human male, and he was not the only male of his time to be an ancestor of people living today. Some of his contemporaries (living at the same time) might also be our ancestors, through the matrilineal line.

Determining how long ago such a person lived is a very different process, because the Y-chromosome is not the same between generations, the way mitochondrial DNA is. The Y-chromosome of an offspring can contain DNA from the mother (from a process called crossing over). Your Y-chromosome (if you were male) and your brother’s are different, and they are both different from your father’s.

Now, perhaps the general goal of each of these two types of study is roughly the same: to find the most recent common ancestor, male and female. However, the scales on which each of these methods is working are so different, and the margin of error so wide for each, that we’ll never narrow it down as far as a single couple. That simply cannot be done. To quote Willow Rosenberg, “It’s like trying to hit a puppy by throwing a live bee at it”. The scientists working on these problems (separately) are not “aiming” at such a couple in any real sense.

In my view, identifying Mitochondrial Eve and Y-chromosomal Adam tells us interesting things about DNA, but it doesn’t contribute all that much to big “How did we evolve?” type questions.

@dappled_leaves , Very good explanation.

I have a question. Do the laws of probability require that eventually there will only be one ancestral copy of the mitochondria? Could the common Eve have theoretically be some pre-human ancestor?

@LostInParadise Well, recall that this search is not looking for the oldest anything. It’s looking for the most recent, and it’s specifically looking at humans as the pool of descendants, so there’s no reason to keep tracing the mitochondrial line backwards to refine the age of Mitochondrial Eve. The first mitochondria would have existed within eukaryotic cells as long as 2 billion years ago (so, well before humans).

But when you ask about probabilities, it makes me think that you are wondering whether this process occurred more than once – whether a single cell engulfed a bacteria, and that cell fathered all eukaryotes, or whether this happened again and again. We really don’t know the answer to that question. As far as I’m aware, we’re not even sure whether plants (remember how the chloroplast resembles the mitochondrion?) and animals are descended from a single ancestor that had a bacterial symbiont, or whether this process occurred once for animals and once for plants.

I think that it certainly could have begun with a single event affecting a single cell. That does not seem farfetched to me.

I had a similar question once. The answer is that all of us do descend from one woman. There were other women but all of those lines died out. We just go back to the most recent woman that we all share DNA with.

@LiLithh13 Welcome to Fluther!

I think it’s an interesting side note that a question about “Eve” was asked by someone whose name resembles Lilith!

While @dappled_leaves does give a fairly decent accounting, albeit somewhat one-sided, I think that you need to consider the alternate scenario.

Once, many, many years ago, six thousand to be exact, the world was a much different place than it is today. For a while we were an entirely uninhabited,water enveloped planet but eventually there arose from the waters a single, giant landmass; the fabled land of Mitochondria which eventually, after a cataclysmic event involving fruit and reptiles, broke apart, by a process known as Mastectomy into several separate and distinct huge, pendulous, islands. Eventually these islands drifted further and further apart until, because the earth is round, they began crashing into each other and breaking apart again and again in what was called Incontinentia by the Greeks, before they went bankrupt the first time, until they formed the seven major continents that we recognize as our planet today. But I digress….

But before this breakup and recombining (called Recombinant DNA in scientific literature). There happened, or was caused to happen, several very important occurrences. Shortly after the solidification of Mitochondria animals of the sea and sky, suddenly and without malice and aforethought, came into existence. Almost overnight these creatures evolved into land based life forms. It was certainly a fortunate happenstance that Mitochondria was present and these animals went on to populate the giant continent. The last and greatest of all these land based mammals was called “Man” (from which we derive such words as Manacle, Mangy and Mandrill) who through “parthenogenesis” brought forth, or excreted, “Woman” (from which we derive the words Woe, WooHoo and Work) from his own body. This act of self-replication, along with several breaks to chase squirrels, took our first man all day and, because the sun was setting before he accomplished the task he, of course, named his excreta “Eve”.

It is because of this, and the fact that this occurred upon the supercontinent Mitochondria, that we refer to this first woman as our “Mitochondrial Eve”. We should, I presume, be thankful that he did not call her Crepuscule.

As a side note it was this “Eve” who upon her nascency turned to see the first males turgid groin ferret and uttered the phrase “AwDamn!” thus giving name to our first male ancestor.

Here endeth the lesson.

@rojo Surely thou jesteth.

Seriously, though, your explanation makes more sense than many of the wild theories spewed forth by the evolution deniers, like that flake who wants to build a Noah’s Ark theme park in Kentucky.

He jesteth. And a damn fine jesteth it was!

It really does make as much sense as creation, too.