Science

Sorry, it's hard to stick not patronising but clear sometimes. Relevant XKCD, although I'm just an enthusiast.

Basically, if broken down mathematically, the fact that life started quickly on our planet may not mean anything. It started sometime in the first 0.5 billion of maybe 10 billion habitable years, which is suggestive, but if the chances are potentially 1:10^100^ every million years (like it might be if a local spontaneous reversal of thermodynamics was required) it's a drop in the ocean. Beyond that the only reason we think abiogenesis might be likely are unfinished guesses at how it could happen, so one could argue we don't see aliens because there never were any in the first place. That's a minority position at this point, so it's interesting.

Uh, so vocabulary that not everyone knows:

Abiogenesis - The start of life for the first time from non-living matter.

Great filter - The galaxy isn't visibly full of aliens, but it should be given the age of the universe. One or more thing (the "filter") stops it from happening at some point on the way to getting there.

Posterior probability - A probability of something reconstructed using Bayes' rule. In this case, the reconstructed chance abiogenesis is likely given that it started early on Earth and we're here to observe it. Not really required to understand the conclusion.

I'm probably safe with habitable planets and the basic concept of evolution of more complex creatures from simpler ones, since this is a science sub.