Sunday, July 25, 2010

Convergent Evolution and Intelligence

Measuring only about one-tenth of a millimeter in length, the female members of the wasp species Dicopomorpha echmepterygis are likely candidates for being the world’s smallest flying animal. Though accomplished fliers, these tiny parasitoid wasps are so minute that one could sit comfortably within the circumference of the period found at the end this sentence. Equally as versed in flight, but dramatically less petite than the insect aviators, were huge pterosaurs like Quetzalcoatlus. Though no human has ever laid eyes on a living specimen, fossil evidence clearly shows that some of these masters of the sky boasted wingspans well in access of thirty feet. In addition to the huge variety of aeronautically inclined insects and reptiles that have been identified, mammals too have converged on the adaptation of winged locomotion; mammals of the order Chiroptera have taken to the sky as moth hunting bats.

Like the adaptation of flight, eyes too have independently evolved in a number of different animal taxa. From the photoreceptive eyespots of a flatworm to the sharply focusing lenses of a great horned owl, eyes have arisen at least forty different times during the Earth’s biological history. ‘Convergent evolution’ is the phrase science uses to describe the common adaptations shared between different lineages of animals. For example, a case for convergent evolution could be made for the possum’s opposable thumb, which may very well represent an adaptation for improved grip; but, this enhanced grasping ability is hardly an indicator of a hereditary tie to primates. Rather than having been passed through genetic transmission from parent to offspring, the opposable thumb simply has an analogous structure and function for both possums and primates. So, just as flight isn’t unique to birds, the opposable thumb isn’t unique to primates.

If not opposable thumbs, is there a trait that is unique to primates? More to the point, is there a trait that is unique to the variety of apes called Homo sapiens? Perhaps intelligence is unique?

Maybe not as unique as we’d like to think:
de Waal, F., & Ferrari, P. (2010). Towards a bottom-up perspective on animal and human cognition Trends in Cognitive Sciences, 14 (5), 201-207 DOI: 10.1016/j.tics.2010.03.003


  1. It looks like (from the very few studies that have been done) the memory system of the octopus has a pattern of synaptic contacts that looks and acts very much like parts of the mammalian hippocampus. It also appears to have a similar function (encoding and maintaining memory stores.) It's my new favorite example of convergent evolution!

    That said, "intelligence" is a tricky construct, because it's so multifaceted and difficult to describe (if it is at all an informative psychological construct.) I don't know how much we can say about intelligence across phylogeny, given how hard it is to define and measure it clearly within humans.

  2. Intelligence (and theory of mind) are most certainly not unique to humans, nor have we yet learned to accurately measure intelligence in other species. For example, we still have not yet learned to "read" porpoises, which have brains as large as ours and whose many species are as social as we. Doubtless, when we do learn how to begin to understand porpoise cognition & communication, we will be astounded and humbled. What a pity that they don't have manipulative hands - I bet they are far more intelligent than chimps.

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