Getting from dolphin to human intelligence is unlikely.
I think this is my current favorite (but not by much): it seems to me that the evolution of human intelligence from ape intelligence may have been contingent on several geographic factors of the early pre-human environment, and a planet where those features don’t occur could be teeming with intelligent life, but nothing quite intelligent enough. But I’m not a geologist who could estimate how many randomly chosen planets would have those features.
Could you clarify which geographic features you mean?
Off the top of my head, I am thinking of the savanna, (which favors height and endurance running, indirectly freeing up hands for tool use) and possibly fluctuating sea level due to glacial/interglacial cycling.
I am not an expert in human prehistory, and I remember reading this account as being speculative the last time I looked into it, so take the following with a grain of salt. That said, it seems that several features of modern humans evolved separately in different environments- color vision in the jungles to identify fruits, standing upright (which led to more useful hands) in the savannah, easy access to micronutrients useful for brain development along rivers and the coast. So if a planet has savannahs and coastline and jungles, but not next to each other like they were in Eastern Africa during the relevant timeframe, then the path that we took is blocked (or, at least, harder to follow).
But how easy are alternate paths, and how likely is a habitable planet to support at least one pathway like that? I don’t have the expertise to guess well.
That said, it seems that several features of modern humans evolved separately in different environments- color vision in the jungles to identify fruits
It’s not clear why color vision is necessary for intelligence. In any case most vertebrates have (at least) three color vision. In most mammals this was reduced to two but in primates a mutation increased this to three. So its not like three color vision is hard to evolve.
It’s not clear why color vision is necessary for intelligence.
I think the more stuff your brain does for you, the more you benefit from any gene that benefits your brain. But is 3-color vision all that different in this regard than 2-color vision? Perhaps not.
I’m not sure about that it seems that the higher up the evolutionary tree you go the more the emphasis shifts from “more senses” to “better use of fewer senses”.
Sharks can detect bio-electric fields and minute water vibrations for example.
The narrow argument would be that, temporally speaking, savannas and colored fruits are rare even on Earth. For any solar-powered primary producer in any theoretical biosphere, there is a basic evolutionary height advantage- you increase the percentage of the time you are in sunlight, spread reproductive tissues over a wider area, and cast shade on nearby competitors. As soon as Earth plants developed vascular systems for vertical nutrient transport (~350 million years ago), forest-morphologies began to dominate the most fertile land areas, so that open areas correlated with geographically distant harsh conditions or a lack of nutrients (deserts, tundra, inland mountains).
The last 60 million years or so have been the exception to this rule, leading to the distinctive savanna ecosystems of the Cenozoic. They really took off after an evolutionary innovation in photosynthesis, C4 carbon fixation, which has its own environmental contingencies. The drought tolerance and efficiency in carbon fixation of these plants are responsible for the existence of ‘fertile’ areas that also have high visibility- and in particular, the close proximity of dense forests and open plains (and coastlines where there are coastlines). As such, the geographic feature is highly contingent on a specific evolutionary pathway within a particular atmospheric regime- and the window could have been closed after a brief period of time by further developments.
The broader argument would point out that, as the wiki page notes, C4 carbon fixation evolved independently a lot, implying that it is closely adjacent to many plant types. The ‘height race’ in terrestrial primary producers may even increase the probability of this development, since it exacerbates the problem of evapotranspiration. If our method of chemical photosynthesis is a common first step in the early development of many planetary biospheres, then C4 carbon fixation may be a common development as well. Whenever you set up primary producers with a certain capacity for internal structure, in cool and dry climates, C4 organisms may be an expected result. We might phrase this argument, ‘the dominance of forest-like ecologies is not stable in evolutionary timescales’.
The even broader argument is that these geographic requirements are not strictly related to savannas and jungles per se; the relevant contingency is ‘environment that selects for erect poses and color vision in a nutrient-rich area’. These factors are not in tension in any obvious way, so we’d need a clever reason to say that this is a great filter.
I think this is my current favorite (but not by much): it seems to me that the evolution of human intelligence from ape intelligence may have been contingent on several geographic factors of the early pre-human environment, and a planet where those features don’t occur could be teeming with intelligent life, but nothing quite intelligent enough. But I’m not a geologist who could estimate how many randomly chosen planets would have those features.
Could you clarify which geographic features you mean?
Off the top of my head, I am thinking of the savanna, (which favors height and endurance running, indirectly freeing up hands for tool use) and possibly fluctuating sea level due to glacial/interglacial cycling.
I am not an expert in human prehistory, and I remember reading this account as being speculative the last time I looked into it, so take the following with a grain of salt. That said, it seems that several features of modern humans evolved separately in different environments- color vision in the jungles to identify fruits, standing upright (which led to more useful hands) in the savannah, easy access to micronutrients useful for brain development along rivers and the coast. So if a planet has savannahs and coastline and jungles, but not next to each other like they were in Eastern Africa during the relevant timeframe, then the path that we took is blocked (or, at least, harder to follow).
But how easy are alternate paths, and how likely is a habitable planet to support at least one pathway like that? I don’t have the expertise to guess well.
It’s not clear why color vision is necessary for intelligence. In any case most vertebrates have (at least) three color vision. In most mammals this was reduced to two but in primates a mutation increased this to three. So its not like three color vision is hard to evolve.
I think the more stuff your brain does for you, the more you benefit from any gene that benefits your brain. But is 3-color vision all that different in this regard than 2-color vision? Perhaps not.
I’m not sure about that it seems that the higher up the evolutionary tree you go the more the emphasis shifts from “more senses” to “better use of fewer senses”.
Sharks can detect bio-electric fields and minute water vibrations for example.
It’s hard to argue that anyone does, I suppose.
The narrow argument would be that, temporally speaking, savannas and colored fruits are rare even on Earth. For any solar-powered primary producer in any theoretical biosphere, there is a basic evolutionary height advantage- you increase the percentage of the time you are in sunlight, spread reproductive tissues over a wider area, and cast shade on nearby competitors. As soon as Earth plants developed vascular systems for vertical nutrient transport (~350 million years ago), forest-morphologies began to dominate the most fertile land areas, so that open areas correlated with geographically distant harsh conditions or a lack of nutrients (deserts, tundra, inland mountains).
The last 60 million years or so have been the exception to this rule, leading to the distinctive savanna ecosystems of the Cenozoic. They really took off after an evolutionary innovation in photosynthesis, C4 carbon fixation, which has its own environmental contingencies. The drought tolerance and efficiency in carbon fixation of these plants are responsible for the existence of ‘fertile’ areas that also have high visibility- and in particular, the close proximity of dense forests and open plains (and coastlines where there are coastlines). As such, the geographic feature is highly contingent on a specific evolutionary pathway within a particular atmospheric regime- and the window could have been closed after a brief period of time by further developments.
The broader argument would point out that, as the wiki page notes, C4 carbon fixation evolved independently a lot, implying that it is closely adjacent to many plant types. The ‘height race’ in terrestrial primary producers may even increase the probability of this development, since it exacerbates the problem of evapotranspiration. If our method of chemical photosynthesis is a common first step in the early development of many planetary biospheres, then C4 carbon fixation may be a common development as well. Whenever you set up primary producers with a certain capacity for internal structure, in cool and dry climates, C4 organisms may be an expected result. We might phrase this argument, ‘the dominance of forest-like ecologies is not stable in evolutionary timescales’.
The even broader argument is that these geographic requirements are not strictly related to savannas and jungles per se; the relevant contingency is ‘environment that selects for erect poses and color vision in a nutrient-rich area’. These factors are not in tension in any obvious way, so we’d need a clever reason to say that this is a great filter.