The Palkeo Est were a humanoid species, meaning they were more than likely seeded by the Progenitors. Superficially, it was very difficult to tell the difference between a Palkeo and a human. Although these humanoids can blend in well with Terrans, distinct differences in their biology and physiology preclude the possibility of genetic hybrids from the two species.
The Palkeo Est evolved on the planet Altair IV. Altair IV's sister planet, the neighboring Altair VI, was once the host to the ancient civilization known as the Krell. The Krell had also colonized Altair IV in the distant past, but fell victim to a plague which destroyed their civilization and wiped them out. It is believed by some that the Palkeo Est were descended from the Krell, although this theory holds very little merit in serious scientific discussion.