Good points. Studies show that Homo sapians interbred with Neanderthals. Results show that Neanderthal DNA is 99.7 percent identical to modern human DNA, versus, for example, 98.8 percent for modern humans and chimps. Since most "humanoid" races look more like Homo sapiens and not chimp for example, then our DNA must be a close match which allows interbreeding without special genetic manipulation as you say. Humans can breed normally with Vulcans, Romulans, Klingons, Betazoids, etc., but not Andorian, Tellarite, short gold guys, etc. because physical similarity equates to DNA similarity.
Good thoughts. Though, do we even know that the Vulcanian, Romulan, Betazoid, and Klingon cross-breeds were conceived normally? I personally prefer the theory that half-breeds we see required some sort of scientific aid. So that they are pretty much a rare sight. Though this would sort of fly in the face of my other seeding theory.
Maybe the reason he is incorrigibly criminally insane...and speaking of the Elba Two insane asylum and our playful inmate Marta, I forgot about Orion green slave women. Breed or not, trying would be fun.
About Orion Animal Women, I prefer the depiction of them in the original script of "The Cage":
SPACE OFFICER (to Pike)
Do any of you have a green one? They're dangerous, I hear. Razor claws, and they attract a man like a sensation of irresistible hunger. . .
Pike is perceptible startled by the familiar term: "Irresistible hunger". And why had Space Officer emphasized the words, and why is he giving Pike that searching look? The Earth Trader is also giving Pike a knowing look. He indicates Pike to the Space Officer.
EARTH TRADER
Now and then comes a man who tames one. (to Space Officer) He'd stumbled into this dark corridor, and then he saw flickering light ahead. (to Pike) Almost like secret dreams a bored ship captain might have, wasn't it? There she was, holding a torch, glistening green. . .
This depiction is much more compelling than that of a sexy dancing girl, or the godawful Enterprise pheromones-power play crap. Here they're more like sirens. They're wild animals that lure men to their deaths. Only occasionally can they be tamed...for...you know.
Personally, I don't consider Marta an Orion Animal Woman. Yes, they have similar external features, but a lot of different aliens in the Star Trek universe look the same. There are probably many other green skinned aliens.
So while it might be fun trying to breed with an Orion Animal Woman, you'd probably just end up getting cut to ribbons with those razor claws.
Breeding compatibility would have been one of the major goals of the project that created all current humanoid life in the Trek galaxy, surely. The folks from "The Chase" wanted that galaxy teeming with spitting images of themselves and having fun together, or at least this is the message they sent to us all.
If they can nudge evolution so that everybody (including the fish!) is a sapient biped, surely they can make sure there's compatibility, either naturally or with minimal meddling said bipeds can achieve early on in their technological history.
My theory, which you are free to disregard, is that the seeding experiment by the aliens in "The Chase" actually failed. Their efforts to direct evolution failed, becasue evolution doesn't work like that. Only one of the species on a planet actually evolved to resemble the "The Chase" species and that was homosapiens and their ancestors. Then as I mentioned up thread some as yet unknown alien force transplanted these species from earth throughout the galaxy. These transplants were genetically modified to adapt them to local conditions and make them compatible with local life. So basically all human looking species were descended from humans. The Tkon, Sargon's people, Cardassians, Klingons, AD INFINITVM; were all genetically modified humans taken from earth at various points in history.
So the seeding plan of the aliens in "The Chase" didn't work as they planned, it did work in a round about way.
Is there natural compatibility in evidence? Gul Dukat had "accidental" offspring, but his mistresses would have been well motivated to make such accidents happen, by whatever medical means this called for. Everybody else would have enjoyed mutual access to the supposedly required technologies.
Timo Saloniemi
True I'd forgotten about that one. But wasn't there some effort in the show to make the Bajorans and Cardassians having been evolved from a common ancestor. I can't remember, so maybe I'm just making that up.