Well then, no, parallel evolution in that sense doesn’t occur. Even if animals become extremely similar externally, so that the average person might mistake one for another, a biologist could tell them apart from their anatomy.
The idea of human-like aliens evolving on other planets is total fiction. It is astronomically (literally) unlikely that independent evolution on two different planets would produce life forms as similar-looking as humans, Vulcans, and Klingons. (Perhaps some primate-like life-form could evolve, but I think it would be instantly recognizable as different from any terrestrial life form.)
The idea that parallel evolution could produce life forms on different planets capable of interbreeding is even more absurd. That doesn’t even happen on this planet, where life shares ancestry. It would even be unlikely that alien life forms could even be able to eat the same foods as us (due to different isomers of organic molecules, different amino acid ratios, etc.)
This device in science fiction is mainly (1) to enable humans to relate to the aliens (2) even more important, to keep makeup costs down.
My own favorite example of parallel evolution is the Australian thorny devil (Moloch horridus) and the North American horned lizards (“horny toads,” Phrynosoma sp.). Both are desert-dwelling lizards with flattened bodies covered with spines, which feed almost exclusively on ants. They look much more like each other than like any other genus of lizards, but they developed in widely separated geographic areas and belong to different families.
If I recall the common ancestor was protoplasm. Not primate. While certainly a common ancestor, I’d hardly rank that any higher than a puddle of amino acids as an ancestor. Plus they ripped the idea off from Larry Niven’s “Known Universe” wherin the galaxy was seeded with proto-foods to be harvested to feed the Thrint. After the Thrint died the protoplasm was mutated over many millions of years, giving rise to all known planetary life forms other than Bandersnatchi and some pre-collapse specis kept alive in stasis. Of course starseeds and “Outsiders” are exempt.
Damn you Demostylus, beat me to it (by quite a long margin).
Here’s a few artists interpretations of what Thylacosmilus might have looked like, including the very weird looking facial flanges to accomodate the sabre teeth.
I’m surprisingly quick, despite these freakin’ gumboots on my feet (which are down below my hairy knees). I know you Poly, and you know me: I’ve got to be a joker and I do what I please.
Not even a common ancestor; the explanation was that a humanoid race, to commemorate itself, had codged the dawn-of-life DNA on various planets so that it would ultimately produce humanoids.
Needless to say, it’s garbage, unless you postulate different genetic laws in the ST universe - i.e. directed evolution. With interbreeding so commonplace, it should have been blindingly obvious that there was some common origin. And yet the internal differences - eg. Vulcan copper-based blood, Klingon eight-chambered heart, etc - make nonsense of the idea of viable interbreeding.
They were, of course, carnivores. And I’ll bet they ate a few of our primitive ancestors. Can you imagine poor cave man Og coming home from a hard day gathering and hunting, only to find one of his children missing. His cave wife explains to him that, of course, it is not her fault and instead of blaming her for the loss he should (you know it’s coming) blame it on the Bossa Nova.
Sorry. Someone had to do it.
Anyhow I was thinking on my own question and had a modified but related question to ask about a specific specis of animals. I"m told that dogs are descended of bears. Is this true? If so, did dogs evolve from bears after the continents were divided and thus evolve in paralell? As anyone knows dogs can breed between specis (and will try and try until you turn the hose on them).
Dogs can breed between breeds, but all domesticated dogs are the same species – Canis familiaris. (Canus lupus is the wolf, but I’m not really certain that these should actually be seperate species, as I believe they can sucessfully breed. Correct me if I’m wrong.) Dogs are in the family Canidae, and bears in Ursidae, both in the suborder Carnivora. But I don’t think you could really say one evolved from the other. Both (along with Cats, Mongooses, Hyaenas, Weasels, Walrus, Sea lions, Seals, and Raccoons) evolved from a common ancestor that lived tens of millions of years ago.
They can interbreed, they just normally don’t breed in the wild. That’s one of the conditions of being a seperate species, but the exact definition of species is open to interpretation.
Domestic dogs are Canis lupus familiaris - a subspecies of the Grey Wolf. The two can interbreed, and are, in fact, now considered to be of the same species.
The family Canidae is older than the family Ursidae by about 10(-ish) million years. As such, at the very least, the chronological order is backwards for dogs to have evolved from bears. More to the point, Canidae is the sister group of (i.e., it shares a common ancestor with) Arctoidea, which itself contains Ursidae several branches in. See here for a cladogram of Carnivora, noting the relative positions of Ursidae and Canidae.
