Primates existed for about 85mln years, Cetaceans for about 48mln years, in all this time nothing got even close to Homo except for Homo. (Evolution of cetaceansEvolution of primates) Of course plenty of other large social animals had an opportunity to develop something like Homo for at least 300mln years before that. (Evolution of Reptiles), or more if we seriously treat possibility of intelligent life in the sea.
So life, animals with nervous system (these are linked, as without nervous system animal complexity is very small), and Homo seem safe.
The case for language and behavioral modernity seems weaker indeed. One obvious argument is that Robin’s paper doesn’t allow reversal to previous states (die-off of genus Homo—something very likely), so if expected lifespan of Homo genus (due to all ecological changes, and assuming no civilization—the bottleneck event theory suggests it’s not too unlikely) was 10mln years, and we expect something like Homo to appear once, then if it took 3mln years, it’s 30% of its possible time, what sounds reasonably hard.
Another case for language is that there is no obvious mechanism how it could have evolved, so perhaps our Homo was luckily predisposed for it. And there’s no reason why you need Homo for something like language—if chimps or dolphins could be taught grammar, that would be evidence for language being easy—yet it seems that in 600mln years of animals with brains nothing like it have happened.
Language and behavioral modernity are so close that they might be extremely closely related. If they’re independent (assuming Homo), we can use expected genus extinction argument.
Or if language turns out to be far older, happening together with Homo (seems unlikely but not impossible), then behavioral modernity needs explanation instead.
Timing as we know it is:
Life << animals with nervous systems << Homo ⇐ language ⇐ behavioral modernity
Homo << behavioral modernity
With exact timing of development of language being unknown.
Primates existed for about 85mln years, Cetaceans for about 48mln years, in all this time nothing got even close to Homo except for Homo. (Evolution of cetaceans Evolution of primates) Of course plenty of other large social animals had an opportunity to develop something like Homo for at least 300mln years before that. (Evolution of Reptiles), or more if we seriously treat possibility of intelligent life in the sea.
So life, animals with nervous system (these are linked, as without nervous system animal complexity is very small), and Homo seem safe.
The case for language and behavioral modernity seems weaker indeed. One obvious argument is that Robin’s paper doesn’t allow reversal to previous states (die-off of genus Homo—something very likely), so if expected lifespan of Homo genus (due to all ecological changes, and assuming no civilization—the bottleneck event theory suggests it’s not too unlikely) was 10mln years, and we expect something like Homo to appear once, then if it took 3mln years, it’s 30% of its possible time, what sounds reasonably hard.
Another case for language is that there is no obvious mechanism how it could have evolved, so perhaps our Homo was luckily predisposed for it. And there’s no reason why you need Homo for something like language—if chimps or dolphins could be taught grammar, that would be evidence for language being easy—yet it seems that in 600mln years of animals with brains nothing like it have happened.
Language and behavioral modernity are so close that they might be extremely closely related. If they’re independent (assuming Homo), we can use expected genus extinction argument.
Or if language turns out to be far older, happening together with Homo (seems unlikely but not impossible), then behavioral modernity needs explanation instead.
Timing as we know it is:
Life << animals with nervous systems << Homo ⇐ language ⇐ behavioral modernity
Homo << behavioral modernity
With exact timing of development of language being unknown.
Good point about the extinction of lineages, TAW. Updating.