Mankind is basically too poor and too stupid at the moment. Building a self-sustaining colony on Mars will require not only tremendous amount of resources, both material and intellectual, but also a transfer of knowledge - which will be impeded by the current legal framework, i.e. copyright laws, for example.
But I do agree with Musk: we must colonize Mars in order to survive the next extinction event.
Mostly too poor and perhaps lacking better engines - we really need nuclear propulsion at the very least (with concomitant big amounts of radioactive material) to not spend a year in space just getting there, which could cause damage, physical and psychological. Or maybe some form of suspended animation.
We cannot really build city sized ships, not yet. That'd require huge space stations.
Self sustaining architecture is one thing, getting it scaled up is another - and relatively hard.
Plus design so as to not cause problems related to living in confinement or in dreary space.
This necessitates at least village scale if not a bigger city.
Other than higher gravity, what does Mars have that the moon doesn't? Both would need highly artificial habitats, with either a steady supply chain or a closed ecosystem, to support human life.
"Poor" and "stupid" aren't helpful terms. The reality is we're heavily disorganized and stagnant, stuck in a scarcity mindset - leading the majority into lower level survival mode behaviour. Leaving it up to capitalism to advance innovation has been interesting, successful, however that doesn't specifically create leaders or organization necessary to solve holistic issues; it certainly has lead to creating pools of wealth especially as automation has occurred, and not being distributed well or fairly. This mess is quickly fixable with the right policies, leadership - educating the population to vote for that, while making sure elections are secure, are foundational supports of that happening; I hope for the world Andrew Yang wins US election, and that the FBI's warnings, along with Mitch McConnell's efforts to block measures securing elections, aren't realized into "Trump" being placed.
But is it really an issue? Were there experiments in low and microgravity on animals? Even then, a third of G is nowhere near as much of a problem as say microgravity or even lunar one sixth.
I'd expect this specific thing to not be a problem - birth may need some assistance which we already know how to do.
How good an analogy are marine mammals? Whales gestate in water, I’m assuming neutral buoyancy isn’t the same as weightlessness when one gets down to the details.
Perhaps aquatic creatures might adapt better to an extraterrestrial environment: Squids in Space!
