Steve Watson

Against the Silurian Hypothesis

Some have speculated that humans are not the first intelligent life to form a civilization on Earth, that there might have been civilizations created by intelligent dinosaurs millions of years ago that have disappeared and because of the effects of time have left no obvious traces. The name of this ‘Silurian Hypothesis’ refers to an episode of Doctor Who[1] in which the Silurians, an ancient reptilian race, attempt to emerge from hibernation after a long absence. The idea in various forms has since had a lot of traction in popular culture[2], and there are also a good number of serious scientific investigations into it – though in the latter case the main interest is not actually in the idea of intelligent dinosaurs but in using that speculation as a point of departure for investigations into the kinds of evidence there might be of any industrial civilization after millions of years.[3]

One critique of this possibility that I never see addressed is that the brain complexity of life decreases very rapidly as one retreats in time. It’s unlikely that there would have been enough brain power before the rise of mammals to create any sort of civilization. Moreover, the encephalization quotient in reptiles generally is very much lower than that of mammals, so that dinosauria would be very unlikely to produce a sufficiently encephalized species to create any sophisticated social order (let alone a technological civilization.)

 And after mammals, the evidence of such a civilization would not have been so thoroughly destroyed that it would be undetectable. In any case, primates are the only likely candidate hosts for a mammalian civilization, and we know their story pretty well, and we’re way above the best of the rest of them.

[1] Doctor Who and the Silurians (TV story) – Tardis Wiki. Note that in this story the Silurians are actually only as old as the Eocene.

[2] John McLoughlin,  Toolmaker Koan, Harry Harrison.  West of Eden, Distant Origin (episode) | Memory Alpha | Fandom

[3] See, for example, G Schmidt & A Frank (2018) ‘The Silurian hypothesis: would it be possible to detect an industrial civilization in the geological record?’ | International Journal of Astrobiology | Cambridge Core. The topic is also well discussed here: Civilization Before Homo Sapiens? | Centauri Dreams