(Science Week, Day 1!)
A couple of tweets from Richard Dawkins last year:
A certain individual in the time of dinosaurs had 2 children. Nobody knows which was elder, nor whether they were of same or opposite sex. Perhaps they played together in the dust. Then they went their separate ways. One gave rise to all wombats. The other gave rise to us.
No it’s not an oversimplification. It’s literally true. All you need assume is the truth of evolution: it then necessarily follows. Not just wombats and humans: a similar argument works for any two species. If you don’t see why, borrow a copy of The Ancestor’s Tale.
I love when authors read their own work, and The Ancestor’s Tale was before the age of audiobooks purchased online. It was only available abridged in North America, but I was fortunate enough to have family in England source a full-length copy on one billion CDs.
It’s a fascinating thought, striking in its simplicity amid such a complex and obscure history. If you happen to know your cousin, you can know your most recent common ancestors are your grandparents, even if you don’t know your grandparents. And you can know that only your grandparents merit that label.
It’s easy enough to see when it’s your grandparents, and it’s almost as easy to see when considering your first-degree cousin: a family member with whom your most recent common ancestors are your great-grandparents (even if you don’t know your great-grandparents). While the counting and digramming gets more complicated, the idea of common ancestry remains simple, and it’s that same idea which is applicable between you and any other life form.
Timbits, once of the goats I grew up with – and myself – share a most recent common ancestor, much further back into the fog of time: an animal that existed at whatever split would eventually give rise to both humans and goats; a much earlier mammal. With my sister’s conure, Tequila, I share a different common ancestor. Since all birds are believed to have survived and descended from dinosaurs, this ancestor would have to have existed before even the split between reptiles and mammals. I’m not expert, but I think that means it may well have been aquatic.
(To explain the title: The Ancestor’s Tale is framed as a backwards pilgrimage through time, starting from the tip of the branch of the evolutionary tree representing humans, heading downward through the larger branches toward the trunk, which represents the origin of all life. Along the way comes a series of meetings with similar “travellers” also heading toward the trunk from the tips of the branches that represent their own species. The earliest encounters are with the species most closely related to humans, the later ones the more distant, and the junctions represent the common ancestor been humans and each. Because going backwards sets these as conjunctions rather than evolutionary splits, Dawkins uses the term “concestor” to represent them.)
What I find the most stirring about this thought is the certainty – while they certainly can’t be known – that the common ancestors for any given pair of life forms on Earth were real. Each resided somewhere, with some way of life, with some survival strategy, with some personality and outlook on the world; all qualities which, going back in time, would seem increasingly alien to us. We’re lucky to have so much evidence for a general picture. But those specifics – those invididual lives – are left to our imaginations.
For day one of Science Week, I’ve sometimes posted this short visualization of known evolutionary history; it’s one link I’m never ashamed to repeat. This year I wanted to focus on that idea of concestry, but I realize the video complements it beautifully, so I hope you’ll watch if you haven’t done so.