Jul 02 2012
One of the themes of this blog is the misreporting of science information in the lay media, so I am always interested in a particularly bad piece of science reporting. Several readers pointed me toward this piece in The Telegraph about studying genetic ancestry. I know newspaper writers usually don’t write their own headlines, but in this case the headline is partly a quote from the article itself: “Scottish lecturer found to be ‘grandfather of everyone in Britain.’”
That is a misleading and useless characterization of the science story covered in the article. The phrase “grandfather of everyone in Britain” does appear as a quote from “scientists”, although no specific name is given. I know from personal experience and talking to other scientists who have been misquoted by the media that the presence of quotation marks does not mean that a real scientist actually uttered those words. It is possible that they did, however. Typically a reporter will interview an expert for thirty minutes or more about the topic of their report, and then use only small bits from the interview, or perhaps none at all. Good journalists will use the expert to help them understand the topic and shape the article they are writing. However, too often journalists (especially those who are not specifically trained as science journalists) will just fish for provocative quotes they can weave into the article they have already mostly written. Even worse, they may put quotes into the mouths of their experts. “Would you say that…”
So when I see terrible statements attributed to “scientists” I always have to wonder if the problem was with the scientist, the journalist, or both.
In any case, you probably don’t know from the headline alone what the article is about, except for a vague notion that it has something to do with genetics. The article is about a Scottish man who had his DNA tested and was found to have a mitochondrial DNA (mtDNA) profile that looks distinctly African.
What this means is that the line of his ancestors that traces back along the female line only goes back to an African female, probably in the last few hundred years. Mitochondrial DNA comes only from the female line (well, almost completely) so it is a way to trace the line of female ancestors. Incidentally, the Y chromosome comes only from males, so that is a way to trace male ancestry.
The history of humanity is an interesting one. It is now very clear that humans evolved in Africa. Africans, in fact, have more genetic diversity than the rest of humanity combined – by far. This means that humans were evolving in Africa for a much longer time than their history outside of Africa, which from a genetic perspective is just one tiny offshoot of the African populations.
Further, the human population passed through a number of so-called bottlenecks in our history – times when the number of human ancestors was reduced to a very small number, perhaps just several thousand. There is still some debate about the number, severity, and duration of these bottlenecks.
A few more points are helpful to make sense of this type of genetic information. First, if you go back far enough everyone is related to everyone else. Think about it this way, you have two parents, four grandparents, eight greatgrandparents, 16 greatgreatgrandparents, etc. You don’t have to go back many generations until the number ancestors you have is more than the population of the earth. The same is true of everyone else on earth.
The solution to this apparent paradox is that many of your ancestors occupy more than one position in your ancestral tree – they are your greatgreatgreatgreatgrandfather, for example, along more than one line, because one set of your grandparents were actually distant cousins. In the end, we are all cousins, if you go back far enough.
This also means that it is very likely that all people living today are descended from every human living in the distant past, especially during times of a population bottleneck.
Researchers have found, however, that all existing mtDNA traces back to a single female living about 190,000 years ago (who they have whimsically and perhaps regrettably nicknamed “Eve”). But shouldn’t we trace our mtDNA back to the thousand or so women living during that particular bottleneck? No, because every time a woman has no children or bears only sons, their mtDNA line ends. Over time, from that bottleneck, only one mtDNA line persisted.
The same is true for the male Y chromosome line, which traces back to a male living about 130,000 years ago (and of course he has been dubbed “Adam.”)
With all this in mind, we can perhaps make better sense of this news item. What geneticists found a bit surprising is that the Scottish lecturer had a mtDNA profile that looked very ancient, especially compared to others native to the British isles. This, of course, does not make him personally to be the ancestor of everyone in Britain, or even that he has the DNA of someone who was such an ancestor. It only means that he has a relatively recent (meaning hundreds rather than thousands of years) female ancestor from Africa. There are many possible sources of this ancestor, mostly involving the slave trade.
That fact is completely unremarkable and unsurprising. I guess that wouldn’t have made such a provocative headline. Still, it is a mildly interesting story that could have been used as a vehicle to explain some basics of human genetics and history. Instead we get an article which does more to confuse than to inform.
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