Scientific Adam and Eve

[Clueless Morgan]

Anthropologists like to use the term "mitachondrial Eve" to describe the common female answer

I think surely there must be more than one though. I can't see how "modern humans" just emorged fully formed at one point, it had to be a gradual transition. Therefore, there was no point in history where there was ever a "first human" or a last ancestor who definitely wasn't human. There are probably several humans who all people descend from, if there's just one male and one female that basically means we're all interbred.

That reads a bit confused. She is defined as the unique individual who is the latest common female ancestor of all currently living humans *in a purely maternal line*. And while we are inbred in a certain sense because we probably all originate from some organism 3 billion years ago or so, there were never just 2 humans - as long as we were anything close to humans, the population size never dropped below several thousands. This is what analysis of the human gene pool tells us

My understanding of Mito-Eve is that she is the human to whom we can trace the mitochondrial mutations that we all currently share.  In other words, when she was born of her mother, she was born with certain mutations in her mtDNA that were unique to her, and that is what scientists can trace our mutations back to, hence why we can pinpoint a specific person as being our Mito-Eve.  We don't know exactly who she was, exactly when she lived, or even much about her, but we are reasonably certain that this one person existed and that she is the individual who happened to be the one whose mtDNA has persisted among the human species.

The same with Y-Adam.

I read an article that I linked in a different post on this thread that its plausible that they could have lived at the same time.

It's possible, but not necessary.  mtDNA is passed from mother to child and can be traced back through the female ancestral lineage.  The Y chromosome is passed from fathers to sons and can only be traced through the male ancestral lineage (since a woman only donates an X chromosome with her egg).  It's not necessary that Mito-Eve and Y-Adam live at the same time, and not necessary that they met, had sex or produced offspring.  It might not even be the case that Y-Adam be a descendant of Mito-Eve since we're talking about the lineage of two different aspects of our genome.

And please correct me if I am wrong, but I thought that speciation was the point where an evolutionary line did branch out on its own? Wouldn't this be a clear distinction in the space time continuum? ok, I don't know what that last part was supposed to mean, I just want to sound smart too :/

Speciation is very hard to put a pin in as to when it occurs; it's more of a concept than a precise moment in time.  As I said before, it's similar to looking at the electromagnetic spectrum and assigning a specific wavelength to when "green" ends and "blue" begins.  There is no clear dividing line, there's a spectrum of definitely-green to definitely-blue with a lot of sorta-greens and sorta-blues and lots of blue-greens and green-blues in the middle.  We know that there is a difference between green and blue, but we can't say exactly where that transition occurs.  It's kinda like this:



There is no single moment in time when you have a Homo erectus giving birth to a Homo sapiens; our delineation of species into kingdoms, phyla, classes, orders, families, genuses and species are taxonomic categorizations that we, humans, impose on the biological world.  The reason creationist harp on about "no transitional fossils" is precisely because there is no hard line between one species and its parent or daughter species.

Why are mules for example sterile? I believe the same went for Ligers, which are real! Does evolution have a safety mechanism that keeps us equal but separate?

Well, mules are sterile because of a chromosomal mismatch (though not all mules are sterile, just most).  Horses have 64 chromosomes and donkeys have 62, meaning a mule (the resulting offspring of a female horse and a male donkey) as receiving 32 chromosomes from its mother and 31 from its father, which leaves one chromosome without a match and ends up screwing up the fertility of the mule.

A female liger can often be fertile, while the male is sterile, so it's not all that similar to mules, which are predominantly sterile with the occasional fertile offspring.  Don't know why.  It could be due, simply, to the genetic distance from each other, but I don't really know.

Here's a freaky thought: Humans and chimps are closer, genetically, than tigers are to lions.  Could we interbreed with a chimpanzee and produce viable offspring?