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Asked by snacks to Anne, Carolyn, Joe, Mariana, Nick on 25 Mar 2010 in Categories: Theories.
Question: Why haven't all creatures evolved with the hippocampus region of the brain?
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Nick Bradshaw answered on 25 Mar 2010:
Eeb, good question.
Well, the hippocampus is I believe found in all mammals but not in other animals. So it is not so much a case of why havent other animals evolved it as much as an early mammal happened to evolve it and it was sufficiently useful that it was passed on to all later mammals.
The hippocampus is involved in long-term memory and spatial functions and is closely realted to the other regions of the brain, notably the cerebral cortex. So in other animals these funcitons (or simpler versions of them) are instead performed in other parts of the brain. While in mammals, having a specicalised area to perform these things is an advantage.
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Carolyn McGettigan answered on 25 Mar 2010:
They just keep getting trickier, snacks!
Well, all mammals have a hippocampus, and this is implicated in all sorts of behaviours including memory retrieval and spatial navigation. It is very distinctive in mammals, having a seahorse-like shape (after which it is named). Even though other species don’t have a structure that looks like this, they do have brain areas that seem to perform similar functions, and have similar chemical properties. For example, the medial telencephalon in birds and the pallium in teleost fish species. A lot of what differentiates the mammalian hippocampus from its homologues in other species is to do with how its shape has been ‘warped’ by the development of our large cerebral cortex, which birds and fish don’t have.
An evolutionary link I find very interesting is that associated with the FOXP2 gene, which has been linked to fine speech motor control abilities in humans and is very highly preserved across animal species. Some research suggests that recent steps in primate evolution may have involved a mutation in the FOXP2 gene that separated humans from other primates in our ability to articulate for speech. This is unlikely to be the only factor meaning that we can speak while other primates cannot. However, it seems that there is perhaps more commonality between humans and songbirds in how this gene is expressed and its effects for vocalization/song than there is between us and chimps.
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Joseph Devlin answered on 25 Mar 2010:
Presumably because most creatures don’t need one. If they did, it would have evolved in them. Obviously, they are perfectly able to thrive in their environment without the burden of memory!
That’s not strictly speaking true. The animals that share a hippocampus may all have a common ancestor if we go sufficiently far back. So other lines of evolution may have produces functionally equivalent structures in other species that I’m not familiar with. In this case, I’m thinking of song birds. I don’t *think* they have hippocampi — although Nick can correct me if I’m wrong — but they certainly have a need for memory. They don’t use the hippocampus in song learning, though. Instead they use a procedural learning system that relies heavily on their version of the basal ganglia.
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