Convergent and divergent evolution
As a zoologist (yes even ichthyologists are zoologists) the way species from different continents with little or no genetic relationship can end up… looking like they might be cousins. Hedgehogs and echidnas. Or if you’re going to look at long, thin sticky tongues and a diet of underground insects, pangolins, anteaters and echidnas. That’s an example of convergent evolution. Different species facing the same problems/needs getting selected toward a similar end-design. But actually their nearest (genetic material) relations are something very different.
On the opposite extreme you have animals which are closely related but not that similar. Chimpanzees and humans… oh, wait. Besides sharing a lot of the same genes, the behavior of chimps and their diet, and social structure are not that divergent. And in looks, well some of you do look like you might be cousins of mine – even if I pretend I don’t know anything about you. But there are other, better examples. Rock hyraxes which bound around the cliffs of Africa and their nearest genetic relative the hippopotamus – which never bounds around cliffs, and can in fact be stopped by a sturdy (very sturdy) knee-high wall. There are assuredly a lot of extinct steps between them and their common ancestor, but one has to wonder if it did live in rivers and lakes and climb cliffs?
One sees the same in many things – from cultures to body shapes, even within a species like ours with huge geographical and environment spread. Look at Japanese rock-climber and say French one. They may look like their national stock in face, but the physiognomy is likely to be similar – because, duh, the requirements of power-to-weight ratio, and upper body strength for optimal brachiating are not dictated by nationality. The same is true of say long distance runners, or Sumo wrestlers. At a somewhat different level I have found scientists working on say fish population dynamics from China or Iceland (I have worked with both) are very like their national stereotype in broad external terms… yet within the working field were more similar to each other, than the Chinese guy was to a Chinese acrobat, or Icelandic guy was to an Icelandic pole dancer or a banker, for that matter.
It’s one of the reasons I find the current fashion of putting people in external characteristic pigeon-holes particularly nonsensical. The Zulu traditionalist has almost no common ground with a wealthy third generation-of-wealth pampered black American author. Both of these have more in common with me (and not all that much) than each other. I understand both imperfectly – but FAR better than they understand each other. But it’s just fine for the black author to write about the Zulu – because of the pigment of her skin, but wrong for me to write about either.
The same convergence is why so many of my American readers found so much to enjoy in Changeling’s Island (1) (Baen) (the text is a link. I get an extra percentage if you use it) –among several of my books with Australian or African settings rather than American – I was writing about people who are very like their those you might find in small communities across a dozen countries and Anglophone cultures. With some exotic differences — but these in a way are largely superficial. The environment that shaped those cultures and those behaviors is some ways very similar. Much the same root-stock of background and cultures went into the mix.
On the opposite extreme I’ve read a few (not all) Australian authors where I had so little in common I might as well have been reading the sf/fantasy of a NYC dweller. The Australian authors I’m thinking of inevitably are relatively successful in East and West Coast US urban centers, and unsurprisingly come from densely populated cosmopolitan urban centers themselves, and from the same social and educational strata as the typical Tor author. Especially given the pervasiveness of the internet at blending cultures, and the slavish imitation of the US coastal urban enclaves by coastal urban enclaves of Australia the biggest difference between the Urban arts grad in trad publishing from either is a confusion about whether it is hot or cold at Christmas.
Anyway, while all of this is interesting and possibly important from the writer’s point of view, why I was bringing this up was because I write sf (and also true, but less so in fantasy), which involve the concept of alien life. Now when designing these, you’re going to hit up against ‘they’re just humans with stick on antenna’ type complaints about the alien creations of many. And to fair I’ve said the same about a LOT of modern fantasy, where the horses (ubiquitous) are remarkably like the automobile, and huge usually medieval high societies exist without the slightest hint of the vast numbers of peasants and primitive agriculture required to support even a tiny landed gentry in the fashion described.
I’ve always found it valuable to posit the drivers of a convergent evolution for my alien species – otherwise, seriously… we might end up hippos meeting hyraxes, or shades of blue meeting colonial bacteria – unaware of the other’s existence, let alone sentience. But given the drivers for a sentience… there is reasonable chance in my opinion, that evolution will solve similar problems in similar Occam’s Razor ways, at least some of the time. Intelligent amoeba there may be, and tri-podal pseudo-lichens with seven sexes. But actually, bipedalism and bilateral symmetry, and binary reproductive strategies solve a lot of problems in the simplest possible way.
The trick, of course is to create the selective pressures. You’re an author. You get to do that.
And from that things flow logically, and you’re much less likely to create implausible beings.
It’s kind of like motive, but at the species level.