The last part of Simpson’s analysis focused on the size of other life forms. Earth animals have a widely known relation between size and the number of individuals — the smaller the species is, the more individuals of that species tend to exist. For example, an alien seeking life on Earth would be far likelier to run into a mosquito than a blue whale.

However, the relation between size and population can also be plotted on a curve against probability, which predicts that the median weight of an alien would be about 692 lbs. (314 kg) — about the size of a bear or an elk. So, based on the results of this model, about half of extraterrestrial creatures would weigh more than that, and half would weigh less. [The 10 Strangest Places Where Life Is Found on Earth]

It might sound contradictory for large creatures to be from smaller planets, but it isn’t: Remember that the populations from small planets, on average, would be small relative to the 7 billion humans who live on Earth.