Brian Clegg brought up an interesting and somewhat confounding point in Henry Gee’s recent post on Missing Links.

Let’s say one does want to take an anthropocentric point of view, and trace a representative human genealogy over time.

Let’s say that one is not particularly interested in the fact that we are cousins with a particular species of coral reef alga. Just like the fact that we are all related here on Nature Network. These family ties are not relevant to how we interact or feel about one another, as they are too distant and tenuous to hold our interest or imagination for long. As an aside, when I understood that another NN member has worked on a similar subject to me at one point, I immediately did feel that sort of tender family connection with her – a scientific genealogy – and this concept has been explored by others, elsewhere.

Now, that last view is an interesting one, because it is linear. That is, if you take the flattened tree view of genealogy, Mr. Badger has done a lot of pruning to focus on the one branch that leads to him. This is a common representation, and I don’t want to criticize it as much as, or as elegantly, as Eric Michael Johnson did. Suffice it to say that such a focus is easily mistaken for implying that each individual is a link in a chain, or a rung on a ladder, that has a destination.

I am going to play devil’s advocate, and say that I do see the justification for this simple presentation, as long as it is understood that there is a multidimensional context, through which one can trace that one-dimensional path in time, between two points: some “ancestor” and yourself. And that there is no destination out there.

What are the parameters?

• Time. Past, present, future. A unidirectional vector.

• Direct ascendance/descendance. Parents, self, children. Siblings are descendants of one or two direct ascendants. Any cousin, no matter how distant, can be described in terms of a mating relationship linking him or her to direct ascendants or descendants. In a spatial coordinate system, ascendance and descendance already occupy three dimensions. I’m not sure if that is because the time component is already inherent, since it is not possible to have descendants before a certain period of time has elapsed in an individual’s life. And we can only make one or a few progeny at a time. Some mathematician should probably come along and set me straight on this.

• Hypothetical situations. What if? The premise of speculative fiction. Go back to a branch point, and take the road less travelled.

When we think about what we have in common with Ida or with Lucy, it’s as easy to write what links us to them. We have a common ancestor, certainly. Where the term “missing link” is very misleading, is that the real genealogy from that faraway common ancestor to the closest organism (in time) with a proven direct ascendancy is entirely in the realm of hypothesis until a fossil is found that can collapse all possible alternative scenarios into the observation of one that really happened. Such a fossil can not be a missing link; it can only be a point from which we can deduce the existence of a branch node – perhaps a new one.

There is a nice, apparently open access discussion of trait evolution here, by David Baum. Notably: “Tree thinking teaches us that all living organisms are equally distant in time from the root of the tree of life and therefore all are equally advanced. Thus, in the eyes of evolution, a human and a bacterium are equally derived. Although one of these organisms is certainly more morphologically complex than the other, both organisms are remarkable in that they are the product of parents that successfully and repeatedly gave rise to offspring over an unimaginably long time span (at least 3 billion years).”

So, more recently, this article (not open access) sparked my imagination, as it began thus:

After the collapse of the Roman Empire in Europe, the Arab dominance across the Mediterranean was one of the most impressive historical events that occurred in this region. Arabs appeared on the southern shores of the Mediterranean in the early seventh century and quickly conquered North Africa. They spread their language and religion to the native Northwest (NW) African Berber populations, which represented the bulk of the Muslim army that later conquered southern Europe. Referred to either as Moors (in Iberia) or Saracens (in South Italy and Sicily), their arrival in Europe dates to 711 AD, rapidly subduing most of Iberia and Sicily (831 AD). Among European kingdoms their presence was seen as a constant danger, and only by the fifteenth century was the Iberian reconquest completed. In the thirteenth century Frederick II destroyed Arab rule in Sicily and between 1221 and 1226 he moved all the Arabs of Sicily to the city of Lucera, north of Apulia. Lucera was later destroyed by Charles II (1301) but an Arab community was recorded in Apulia in 1336. Guerrilla warfare was still conducted by Arabs in Sicily even after Frederick II’s actions.

Imagine what life was like for our common great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-grandmother, Mara (I’ve named her thus), in that little settlement in Sicily, in 787! Because that long ago, she was in nearly all of our families, among the vocal readership of this blog. Assuming a ripe generational length of 25 years is perhaps a little optimistic when facing a nubile young woman in a conquered territory. The authors made reference to another publication in which the generational length was estimated at 31 years, and so only 40 generations away.)

To some probable relief, the authors found that among the populations studied, the southern Iberian peninsula and Sicily have the highest representation of Berber-like genotypes. It’s too bad they couldn’t have collaborated with French or Greek colleagues, or compared their results to similar calculations on an (eg.) Japanese population. But I am not a geneticist, I just hang around with a lot of them.

Anyhow, getting back to Mara – her particular existence is still only postulated, and will remain in that state of suspended animation until proper evidence allies her to someone who exists in the historical record either before or after her.

Should you go out looking for that evidence, and find the record of existence of a woman who lived at the right time in what is now Catania – well, who is to say that it was her progeny who survived and whose descendants were in your family? What if Mara was the half-sister who died in childbirth? Could you tell the difference based on the morphology of her third lumbar vertebra?

It would be impossible to say that Mara was a missing link in one branch of your genealogy until you had a hand on a lot more evidence. Much less the missing link. How much more impossible, then, to affirm that any sort of fossil is any sort of real “missing link”! At best, it can be compatible with a model – an existing one, or what is more fun, a new unifying one. It may rather be a childless cousin, and flesh out missing information on other branches of your family, but you won’t get a piece of the inheritance for all that. You may get a great boost to the imagination, though.
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Capelli, C., Onofri, V., Brisighelli, F., Boschi, I., Scarnicci, F., Masullo, M., Ferri, G., Tofanelli, S., Tagliabracci, A., Gusmao, L., Amorim, A., Gatto, F., Kirin, M., Merlitti, D., Brion, M., Verea, A., Romano, V., Cali, F., & Pascali, V. (2009). Moors and Saracens in Europe: estimating the medieval North African male legacy in southern Europe European Journal of Human Genetics, 17 (6), 848-852 DOI: 10.1038/ejhg.2008.258