Chart 1 shows the encephalization quotient (EQ) of various lineages over time, while Chart 2 shows the maximum EQ of all known fossils from any given time. (Source 1, Source 2. Admittedly this research is pretty old, so if anyone knows of more recent data, that’d be good to know.)
Both of these charts show a surprising fact: that the intelligence of life on Earth stagnated (or even decreased) throughout the entire Mesozoic Era, and did not start increasing until immediately after the K/T event. From this it appears that life had gotten stuck in a local equilibrium that did not favor intelligence; i.e. the existence of dinosaurs (or other Mesozoic species) made it impossible for any more intelligent creatures to emerge. Thus the K/T event was a Great Filter: we needed a shock severe enough to dislodge this equilibrium, but not so severe as to wipe out all the lineages from which intelligence could evolve.
If this is true, then the existence of ravens and elephants today is not much evidence that evolving intelligence is easy, because they exist for the same reason that humans do.
None of this considers octopuses. It would be interesting to see if their brain size history follows similar curves as for the vertebrates illustrated above (but since they’re made up of soft tissue we may never know). If so, then that would confirm the view that evolving intelligence is difficult. On the other hand, it’s hard to imagine that the marine ecosystem would’ve been affected by the K/T event in the same way that the terrestrial was. Or maybe octopuses are themselves what is suppressing the evolution of greater intelligence among marine invertebrates.
Consider the following charts:
Chart 1 shows the encephalization quotient (EQ) of various lineages over time, while Chart 2 shows the maximum EQ of all known fossils from any given time. (Source 1, Source 2. Admittedly this research is pretty old, so if anyone knows of more recent data, that’d be good to know.)
Both of these charts show a surprising fact: that the intelligence of life on Earth stagnated (or even decreased) throughout the entire Mesozoic Era, and did not start increasing until immediately after the K/T event. From this it appears that life had gotten stuck in a local equilibrium that did not favor intelligence; i.e. the existence of dinosaurs (or other Mesozoic species) made it impossible for any more intelligent creatures to emerge. Thus the K/T event was a Great Filter: we needed a shock severe enough to dislodge this equilibrium, but not so severe as to wipe out all the lineages from which intelligence could evolve.
If this is true, then the existence of ravens and elephants today is not much evidence that evolving intelligence is easy, because they exist for the same reason that humans do.
None of this considers octopuses. It would be interesting to see if their brain size history follows similar curves as for the vertebrates illustrated above (but since they’re made up of soft tissue we may never know). If so, then that would confirm the view that evolving intelligence is difficult. On the other hand, it’s hard to imagine that the marine ecosystem would’ve been affected by the K/T event in the same way that the terrestrial was. Or maybe octopuses are themselves what is suppressing the evolution of greater intelligence among marine invertebrates.