Convergent Evolution

[Zendexor]

I am researching the topic of convergent evolution versus common-origin assumptions - regarding humans found on other worlds.

I know that Edgar Rice Burroughs was a convergent-evolution man - his Barsoomian red men are human enough to mate with Earthmen, but nevertheless evolved on their own world, originating in the Tree of Life near Mars' South Pole.

I believe that Leigh Brackett's Mars on the other hand - and the rest of her Solar System - is peopled by descendants of some ancient starfaring race, but I can't recall chapter-and-verse to back up this memory. So she goes for the common-origin option - if my memory serves me properly. Can anyone confirm this?

 

[Ray McCarthy]

However even with convergent evolution the species only seem similar. They can't interbreed at all.
So Donkeys and Horses can mate (poorly) due to common ancestor not so long ago, as can Tigers and Lions.
Dogs and Wolves can too. But the extinct in about 1926 Tasmanian Tiger / Wolf, was an example of convergent evolution. However it was actually a Marsupial and could not have interbred with a canine etc.

The flying squirrel and "sugar gliders" are totally incompatible even though look similar (Mammal and Marsupial). The sugar gliders are sometimes even called flying squirrels. That's convergent evolution.

A Panda isn't a bear, it can barely breed at all, never mind with anything else. Maybe a little related to a racoon. Koala of couse isn't a bear either.

Almost everything to do with Evolution is garbled in the popular press and outside trained scientists. Evolution doesn't even say anything about life's origin here, only how it developed, nor anything about how life might arise elsewhere.

Convergent evolution is never going to give two species without a reasonably close common ancestor ability to interbred.

Elbert A. Rogers argued: "If we lean toward the theories of Darwin might we not assume that man was [just as] apt to have developed in one continent as another?" In fact humans didn't separately evolve on the different continents from separate distinct ancestors but all come from a single group in a single place and spread out from Africa via Middle East to the whole world.

EDIT:
I think the Shark and Dolphin are cited as examples of Convergent evolution. They are of course only superficially similar. Sharks need flowing water or suffocate, they are a "primitive" type of fish as they have cartilage instead of a boney spine, they lay sack like eggs. Dolphins are mammals and breath air.

Here are some examples:
https://en.wikipedia.org/wiki/List_of_examples_of_convergent_evolution

Of course in SF & F you can postulate anything you like. It's argued by biologists that for more advanced species it's likely that:

• Bilateral Symmetry
• Four limbs
• Front limbs paws or hands can grip (Panda has an appendage that looks and works like an opposable thumb but is quite different).
• A head at end.
• Skeleton, rather than shell.

But need not be a placental mammal. This is all based on principles of convergent evolution. So my SF worlds (and some fantasy) are populated by every kind of creature, including some hypothetical types that don't exist here, but they are all "human like" and often can't even get proper nutrition from otherworlds (food lacks the kinds of things equivalent to amino acids and vitamins. c.f. Rabbits and Cavies vs need for Vitamin C, or creatures on earth with vastly different nutritional needs, even though fat, carbohydrate and protein might be mostly compatible). Convergent evolution allowing different origin species to breed would be more remarkable than any miracle in the bible.

 

[hitmouse]

What Ray McCarthy said. In convergent evolution, different species evolve to fill similar ecological niches. As a result, general body morphology (or specific features of body morphology) tend to develop similar design solutions. This is not the same as suggesting that animals that look similar will be able to cross-breed in any way at all. It is found when comparing isolated ecosystems e.g. Eurasia, Americas, Madagascar, Australia, Tasmania.I do not really think that ERB ever seriously considered this from a scientific position.

 

[Zendexor]

What Ray McCarthy said. In convergent evolution, different species evolve to fill similar ecological niches. As a result, general body morphology (or specific features of body morphology) tend to develop similar design solutions. This is not the same as suggesting that animals that look similar will be able to cross-breed in any way at all. It is found when comparing isolated ecosystems e.g. Eurasia, Americas, Madagascar, Australia, Tasmania.I do not really think that ERB ever seriously considered this from a scientific position.

Yes I know ERB was not being scientific but art creates its own rules and it is those rules I am interested in primarily. With Leigh Brackett the evidence is contradictory. In People of the Talisman the non-human Martian says to its human Martian captives, "we are the oldest race on Mars. We knew you before you walked erect" - which suggests that the Martian humans in the story evolved on Mars. On the other hand in The Secret of Sinharat, another Eric John Stark tale, it is stated that the humans of Mars, Earth and Venus were "descendants of some parent human stock that long ago had seeded the whole System". The only way I can think of to reconcile those two statements is to postulate that the "parent human stock" was the ancient Martians themselves, who in their heyday must have had interplanetary travel... You see the game I'm playing: taking it all seriously and trying to work out how it could hang together. But I would prefer the ERB-style convergent evolution to the Brackett common-origin; though it is less scientific it is artistically more satisfying.

 

[Ray McCarthy]

but art creates its own rules and it is those rules I am interested in primarily. With Leigh Brackett the evidence is contradictory.

Make your own "rules" then. But SF particularly can end up seeming childish and stupid if it's got stuff inherently impossible (then it's just fantasy like frog princes) or no internal logic or wilfully ignores science for no good plot reason.

You can have your species origins anything you like, but best not to try and explain why or how people on different planets can interbreed, unless you are saying they are the same species. Spock in Star Trek is supposed to have Vulcan father and human mother. Best not to try and explain something like that as it's "naturally" impossible, a virgin birth is more feasible.

I suspect ERB and Leigh Brackett didn't think about the biology and genetics at all and just wrote the stories. If you are writing, don't worry about what were their intentions.

 

[hitmouse]

Didn't John Carter and Dejah Thoris produce an egg? Doesn't stand up to any sort of biological scrutiny really. Why does Dejah have breasts?

 

[Ray McCarthy]

Chickens have nice edible breasts, and eggs.

As I said, ERB wasn't paying any attention to biology. Really there is no point in trying to analyse it. It wasn't a documentary.

 

[Danny McG]

Didn't John Carter and Dejah Thoris produce an egg? Doesn't stand up to any sort of biological scrutiny really. Why does Dejah have breasts?

Dejah had breasts to look hot on the pulp covers eagerly gazed at by my 14 year old self (That kid seems almost a stranger all these years later)

 

[Ursa major]

Last month, there was an article in The Economist magazine about this topic with reference to giant pandas and red pandas (the former a type of bear, the latter distantly related to weasels and raccoons). What these animals have in common, apart from the name, panda, is that they are vegetarian members of the order, Carnivora.

The Institute of Zoology in Beijing compared these pandas' DNA, together with the DNA of polar bears, ferrets, tigers and dogs. They team at the institute found ten genes that have been disabled by "crippling" mutations in both the pandas, but not in the others. Some of them fell into one of three categories: genes affecting anatomy, genes affecting appetite and genes affecting digestion and the metabolism of nutrients.

To cut a long story short, the pandas share (presumably quite by accident), certain genetic peculiarities that support their vegetarian lifestyles. (This doesn't mean that convergent physical evolution necessarily depends on near identical changes in the same set of genes in different animals.)

 

[Galactic Journey]

ERB hardly wrote science fiction (as we know it). What terrific stuff, though, particularly the Pellucidar and Caspak series!