Alien Imagination

Attempting to define parochial features challenges many taken-for-granted notions about morphological necessity. Skeletons, which are essential to large terrestrial organisms according to the experts of the field of gravitational biology, are almost assured to be replicated elsewhere in one form or another. Many also conjecture as to some type of egg-laying amongst extraterrestrial creatures, but mammalian mammary glands might be a singular case.
The assumption of radical diversity amongst putative extraterrestrials is by no means settled. While many exobiologists do stress that the enormously heterogeneous nature of life on Earth foregrounds an even greater variety in space, others point out that convergent evolution may dictate substantial similarities between Earth and extraterrestrial life. These two schools of thought are called "divergionism" and "convergionism" respectively.