"The Chase" is as scientifically stupid as "Genesis" or "Threshold." Evolution doesn't have a predetermined end point like the episode suggests.
But that's just what the episode
doesn't suggest. On the contrary -- the whole point of "The Chase" is that natural evolution
would not have produced humanoid forms on so many different worlds as some kind of inevitable endpoint -- that such forms only came about because a hyper-advanced DNA-based nanotechnology (essentially) had been seeded on those worlds and had been
directing the evolutionary process from the inside, artificially guiding it toward a preprogrammed goal that couldn't possibly have come about naturally. The episode acknowledges that humanoid aliens don't make evolutionary sense, and justifies them by establishing humanoid life in the Trek galaxy as an artifact, a result of technological intervention.
Yes, it's silly compared to reality, but humanoid aliens are something we're stuck with, a necessary evil for a live-action TV series. Acknowledging that they could only have come about through artificial intervention is, to me, a good thing, though naturally one can quibble about the details.
If the aliens really did seed planets with life, they did a piss-poor job of it because evolution didn't take off on Earth for a few billion years after the seeding.
Multicellular evolution didn't take off until then, but even today, the majority of life on Earth is unicellular. No doubt the First Humanoids understood that they couldn't force the process, that they needed it to develop at its own pace, just with guidance at key points. It took the entire panoply of terrestrial biology to lay the foundations for the emergence of hominids.
Plus, the message encoded in the DNA would have been just as present in every dog and every tree on Earth.
Yes, but there are lots of things in biology -- and probably in computer science and other fields -- where a control process or mechanism is situational, where it's present in all contexts but only expresses itself in specific contexts where it's triggered by environmental or situational cues. Like how every cell in the body contains the entire genome, but some express the genes that turn them into muscle cells while others express the genes that turn them into blood cells, etc.
Besides, it's not just humans that are duplicated on other worlds. We see similar vegetation on planets all over the galaxy. We see alien variants of horses, dogs, birds, fish, and other Terrestrial animals -- not to mention aliens that are humanoid versions of cats, reptiles, and the like. Clearly it's not just humanoid DNA that the First Humanoids seeded, but the DNA for their entire biosphere, which has been approximately duplicated (or mixed and matched) on worlds throughout the galaxy including Earth. Which only makes sense, of course, since we share the vast majority of our DNA in common with the other life on our planet. It would've been impossible for them to seed humanoid DNA without seeding DNA that would produce other related forms as well.
And it doesn't even have The Beatles in it.
Doctor Who's "The Chase" can at least boast of that.
Well, I can't argue with that.