FAQ
A contribution of The Cephalopod Page
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| I am quite frequently asked some version of the following question: |
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| To me this is a very interesting question and something that I've though a lot about.
It is hard for us, as mammals to understand why a fairly large and intelligent creature such as an octopus lives for only a year. I think the answer is easier to understand if the question is altered slightly to 'Why would evolution favor cephalopods to have large brains and well developed senses'. A large brain could help any animal regardless of its life span. Cephalopods were once one of the dominant groups in the worlds oceans. Cephalopods faced competition from a relatively intelligent and fast moving commentator. When fish arrived in the world oceans - many species of cephalopods went extinct but some, those that were able to adapt by losing their heavy external shell and becoming faster as well as developing better senses and larger brains to process the increase in information, survived. A large brains seems worth the cost in cephalopods, in say a clam, diverting resources to a large brain would not be selected for as that energy could be put to better use elsewhere. Evolution looks at brain size just like any other hunk of material. If having that bit become larger, be it muscle, brain or gonads helps the animal survive and produce fit offspring them natural selection will favor it. Still it is hard for us, as mammals, to not link intelligence with life cycle. We are most familiar with the life cycles of cats, dogs, birds, rodents, elephants, fish and other vertebrates, many of which have relatively long life cycles and are iteroparous (reproduce more then once). However, cephalopods are not the only creatures that reproduce once and die, salmon are a vertebrate example of an animal that only reproduces once. And as far as life cycles go, there are far weirder ones out there. Many jellyfish and hydrozoans have alternation of life style and many species of algae experience alternation of ploidy in addition to alternation of life style. The life cycle of many parasites is truly bazaar and interesting. Cephalopods, except Nautilus, are though to live fast and die young. They do not store lipid reserves like fish. Therefore, it might be better for them to get to maturity as fast as possible and get out a second generation instead or surviving a lean period. Keep in mind that a lean period for an adult may be a good period to be a hatchling that is several orders of magnitude smaller and feeding on a completely different food source. Also, jet power isn't as efficient as fin undulation except at very small sizes. Having short life cycles may help cephalopods spend a large part of their life in a stage where they have the advantage. Dr. James Wood |