so which came first: the chicken or the egg?
Semantically speaking? Evolutionarily speaking? Speaking in terms of species?
If it can be just any old egg – the egg came first. By a long, long, long time. If you mean a chicken egg (and I’m pretty sure you do), then it depends on how you define a chicken egg: is it one that was lain by a chicken – or what that hatched a chicken?
Because every chicken hatched from an egg. So at some point, the very first totally-absolutely-definetely-a-chicken hatched out of an egg that had been lain by an almost-but-not-quite-a-chicken. But if you want to be technical about it, then that was not a chicken that laid it, so it was not a chicken egg.
(I’m not helping yet, am I?)
BUT REALLY: It all depends on which definition of species you want to use.
- Living bio-species (what we see around us and how we normally use the term) distinguish different populations that incapable of breeding with each other for more than two generations. This is where we have the problem with the riddle – because bio-species definition doesn’t accommodate evolutionary long-term change occurring in deep time.
- But, you might want to talk about a morpho-species: a group of organisms that share enough anatomical traits that we’re pretty damn sure they could breed. (This is what we usually work with in the fossil record. we identify body shapes and forms and we have to guess about whether they could breed with each other depending on how similar they are. We’ve gotten pretty good at it. Sometimes we call them palaeo-species, just to be clear that this is how we identified them. But we’re still trying to match a model of bio-species. Which may or may not even be the right model to match…)
- If that isn’t good enough for you, we can talk about chrono-species: or a lineage of organisms who descended from each other, while changing in body shape.
Think of it this way: you’ve got Thing A which over time changes form and evolves into Thing B.
All members of Thing A and Thing B can breed.
But then the valley floods and all the Thing As on one side die out from some disease that was in the water that only Thing Bs can survive. (There’s still some left on the other side of the mountain range but no one knows how to get there.)
With more time, Thing Bs slowly have children and grandchildren and great-grandchildren who look and act so different that we call them Thing C.
Thing Bs and Thing Cs can breed, no problem – but if one last remaining Thing A was found (managed to make it across that mountain range because the rest of its people had starved and it was hoping for a better life) and it’s only hope of having a child was meeting a Thing C? We’d have a problem.
So how many species is that? Three? Two? Thing AB and Thing BC? Or just Thing A and Thing C?
If you’re talking about a lineage (since we know for certain that Thing A was ancestral to Thing B and Thing B to Thing C), then they’re one lineage. Which is totally a chrono-species. ONE SPECIES.
But – if you’re talking about a morpho-species: we’ve got three separate species.
BUT – if you’re talking about a bio-species: …well. That’s the problem, isn’t it? Where do you draw the line?
And, if you’re talking about the fossil record – where you can never even be sure whether the piece of an ankle that you found belongs to a Thing A or a Thing B because you defined the groups by what their teeth look like…
(Plus, it turns out that there’s also Thing 3, which is probably a “cousin” of Thing B because it looks kind of like Thing A, but definitely didn’t help make Thing C but no one really knows because all they care about is Thing X and trying to figure out who’s its ancestors are.)
You might just give up on the whole idea of “species” altogether and start talking about “clades”. Because when you say clade you just mean a group of similar things and don’t have to judge whether their affinity is at a species/genus/family/population level.
(Except – just wait – in another fifty years time we’re all going to be debating what “clade” means because it will have picked up a bunch of baggage.)
After all, “species” is just a name we made up to help us squeeze things into boxes. Because as humans with human brains, we like boxes and categories.
Feature Image: from AsapSCIENCE, 2013