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They have the same secondary sex traits - as species-specific as you can get.Only their males have much facial hair, and their females often have bodacious figures. This leads to some speculation that they may be of Earth Human descent.(Or else Earth Humans are descended from them, though this raises troublesome questions about chimpanzees.)Perhaps because of these awkward issues, Aliens with Forehead Ridges have become much less common in written SF (save for media tie-ins) than they were some decades ago.
This is for an obvious reason: the audience wants aliens of One of the first ways in which we learn to classify objects is into two groups: 1. Nevertheless, the task of defining "life" is both difficult and subtle; something that at once becomes evident if we stop to think. The caterpillar is alive, but the rock is not; as you guess at once, since the caterpillar is moving and the rock is not.
More specific and etymologically correct than sentient.
Still less common than that term, but has been used by multiple writers..
Sometimes they look rather less like humans, in which case (if friendly) they often resemble large teddy bears.
Not only do Aliens with Forehead Ridges mostly look like Earth Humans, they tend to act like Earth Humans as well, or at least one particular (real or speculative) Earth Human culture.
A particular race of Aliens with Forehead Ridges may all have a culture like that of medieval Japan, or one based entirely on music, but you will very rarely find more than one culture per species.