Tuesday, August 6, 2013

Y and mtDNA are not Adam and Eve: Part 1

 Co-posted at Panda's Thumb. If you'd like to comment, please join the discussion here.

This is going to be the first of a several part (at least two, maybe more, however many it takes) series of posts discussing both the science and the science communicating regarding a recent paper:
Science. 2013 Aug 2;341(6145):562-5. doi: 10.1126/science.1237619.

Sequencing Y chromosomes resolves discrepancy in time to common ancestor of males versus females.

First, you should go read it. It is short and sweet, and, yay science!

What I'm going to talk about first is how this paper relates to communicating science. Future posts will expand and elaborate on the research. I'll also note that I am not picking on this paper alone, because several other scientific papers have done the exact same thing. This one is just the most recent incident, and, more personally,  I was actively involved in trying (and failing) to prevent the miscommunication. As such, I feel the need to provide more explanation.

The recent paper did an excellent job of publicizing itself. It has a sexy title, and it mentions, "Adam and Eve" in the main manuscript:
"Dogma has held that the common ancestor of human patrilineal lineages, popularly referred to as the Y chromosome "Adam," lived considerably more recently than the common ancestor of female lineages, the so-called mitochondrial "Eve."
Regardless of the results (which are definitely new, and we'll discuss later), these things alone would get it a lot of press. They are tangible ideas that the public can relate to, and make it easy for a science journalist to build a story around.

But, they are also extremely misleading. I think they are also harmful, in the long-term for educating and communicating with the public.

I was interviewed by two different science writers to comment on this paper, and in both interviews I stressed how inappropriate the "Adam Y" and mitochondrial or "mtDNA Eve" analogies are. You can see how well they took that into consideration: here and here. I really enjoyed talking with the journalists, so hope they won't think I'm picking on them either because, to be fair, nearly every popSci article used this analogy (see here, here, here, and here). I'll take a sentence here to especially note the article by Francie Diep, here, that took a different approach.

While I have several reasons to disliking this analogy, I cannot fault the journalists completely for using it in this instance. Aside from my protests, there is no reason science journalists should think that it is a bad analogy, because it was used in the manuscript (without context or explanation).

Okay, so I'm upset that the paper would reference the "Y Adam" and "mtDNA Eve" without explaining them, but why are these analogies wrong? The public connects to them - they are visual and engaging, so what's the problem?

First, a little background:

Who are Adam and Eve?
If you are not familiar with it, in the Old Testament, one of the creation myths is that God created a man (Adam) and a woman (Eve), and all other humans are descended from this pair of first humans.

Simple enough.

What are the Y and mtDNA?
Each person has half of their DNA from their genetic father (who provided the sperm) and half of their DNA from their genetic mother (who provided the egg).

The Y chromosome passes through the genetic male lineages (genetic males are XY, inherit their Y chromosome from their genetic father, and will pass it on to their genetic sons).

The mtDNA is a small circular piece of DNA that all of us have in our cells, but is only transmitted through the genetic female lineage (the egg contains the mtDNA, so although genetic sons and daughters both receive this mtDNA, only the genetic female lineage makes eggs, so mtDNA is only passed on by daughters).

The Y and mtDNA are unique
Unlike the autosomes, which come in pairs (one copy from genetic mom, one from genetic dad), and can swap DNA, resulting in the mixing up of information from genetic mom and dad, neither the the Y chromosome nor the mtDNA have a partner (Y only from genetic dad, mtDNA only from genetic mom). So, it is somewhat simpler to trace these two pieces of DNA back in time.

Using some math and observations of the numbers of observed changes (mutations) on the Y chromosome and the mtDNA, scientists can estimate how closely related any two Y chromosome, or any two mtDNA are, and when they last shared a common ancestor.

What's the problem with "Y Adam" and "mtDNA Eve"?
If we can estimate the most recent common ancestor of the mtDNA and the most recent common ancestor  of the Y chromosome, isn't this kind of like the creation story of Adam and Eve?


There are several reasons people don't like these analogies, but in my opinion there are two overwhelmingly wrong ideas that get propagated when using them. Applied to genetics, using the creation story of "Adam and Eve" to describe the most recent common ancestor of the Y and mtDNA, respectively, implies that:

Bad analogy #1: There were only two humans alive at that time.

There were several other genetic females living at the time of the person who carried the mtDNA ancestor of us all, and several other genetic males living at the same time as the genetic male who carried the Y chromosome ancestor of modern genetic males.

Bad analogy #2: Y "Adam" knew (presumably intimately) mtDNA "Eve".

Just because the person who carried the ancestral Y chromosome is predicted to live about the same time as the person who carried the ancestral mtDNA (120,000-156,000 years ago for the Y lineage versus 99,000-148,000 years ago for the mtDNA lineage), in no way suggests that they lived at exactly the same time. Although it is short on an evolutionary time scale, those are pretty big time ranges when you're thinking about a human lifespan! Further, even if they happened to live at the exact same time, there is no evidence that they were located in the same region or would have interacted at all.

These two erroneous assumptions stem directly from using the "Adam and Eve" analogy. The public is smart, and while they may not have the vocabulary (heck, people outside of our specific sub-disciplines do not share the same vocabulary), they can understand analogies. When we, as scientists, supply an analogy that doesn't accurately describe the research, it is not the public's fault for misunderstanding the work; it is our fault for misrepresenting it.

There is no reason why the "Y Adam" and "mtDNA Eve" should have been mentioned in the primary manuscript, but if it was necessary, it should have clearly been explained why this analogy is not appropriate.

Well, that's a start.

In the follow-up posts I will go into:
1. More detail describing bad analogy #1 and #2 above, and misunderstandings relating to the title
2. An accessible research summary of the actual paper (yay! - This really is the most fun part.)
3. Addressing questions you all have about this topic!

So, stay tuned!!

Part 2: http://mathbionerd.blogspot.com/2013/08/y-and-mtdna-are-not-adam-and-eve-part-2.html
Part 3: http://mathbionerd.blogspot.com/2013/08/y-and-mtdna-are-not-adam-and-eve-part-3.html