Living on a planet comes with certain advantages. Gravity, for instance. The only reason hot air rises on Earth is that colder, denser air will always fall to displace it upwards. On the International Space Station everyone has to sleep next to a fan or they end up being enveloped in a bubble of their exhaled carbon dioxide (or worse).
Perhaps this won’t be a problem for life forms that evolve in microgravity, since they might evolve to keep moving around all the time, even when sleeping – kind of like how sharks do in Earth’s oceans.
But then, life forms that might evolve in microgravity are unlikely to be metabolically dependent upon either atmospheric gases or oceans, since if you are going to have an atmosphere or an ocean of any appreciable density – you kind of need something like a planet to start with. Hmm…
So, can something interesting evolve in microgravity, in the the absence of a dense medium? Well, there’s Sir Fred Hoyle’s fictional Black Cloud – where something approximately 1 AU in diameter, with the mass of Jupiter and considerably less density than water still managed to be hyper-intelligent, despite the substantial impost placed on its speed of thought. I mean, that’s eight minutes travel time just to go hmm…
Our one and only data point about how intelligence might arise organically suggests an electrochemical basis, while the hypothesized Black Cloud required an electromagnetic basis. The latter is feasible in a brain with a density considerably lower than water, but you would need to transmit thoughts at the wavelength of X-rays to effectively move them through the dense organic tissues we are familiar with on Earth. On that basis, too much thinking really could give you cancer.
So, it seems plausible that intelligent, electrochemical thinkers generally evolve on planets – but we can still keep it open for some much bigger, though perhaps slower, electromagnetic thinkers to evolve in microgravity.
And there are reasons to envy an entity that can survive long term in microgravity and can manage a slow and steady journey between stars under its own propulsion system. For us high density thinkers, there’s a time limit on just how long you can enjoy the particular gravity well you happen to have evolved in. Habitable zones don’t stay habitable forever. Firstly, gravity wells have a habit of attracting devastating meteor or comet impacts – and for the longer term, your star is eventually going to die.
Probably, the smart thing to do first is to build a planetary defense system – noting the current population of dinosaurs on Earth is exactly zero. In the longer term, you would need to make a run for it – ideally taking as much of the surviving ecosystem with you as you can. You never know when some giant energy-sucking alien artifact is going to show up, wanting to talk to a whale.
Anyhow, it’s great that we are now in orbit on a regular basis. It’s a really good start.