Talk:Cephalopod ink

Pictures

Does anybody have a picture of an octopus or squid inking? The only ones with a usable licence I have found [1] and [2] are not very good and do not allow derivative works (i.e. no cropping) K-22-22 (talk) 10:47, 8 December 2008 (UTC)

Not that I believe in such things but

Isn't it kind of silly to assume snail ink is convergent evolution when it's just as likely to be a retained trait from a common inking mollusc ancestor, or something all molluscs have that's just undeveloped in other molluscs? It's not as if youve traced the ink DNA.. —Preceding unsigned comment added by 64.122.208.21 (talk) 15:57, 3 March 2009 (UTC)

No, this is not a silly supposition and this is the reason. The majority of modern mollusc species do not ink. Just a few do. Therefore, if the sea hare and the cephalopods had a common ancestor that did had ink, then every species that doesnt ink now, and also has that common ancestor, would have had to lose the ability to ink in the geological time elapsed between that divergence. If the two mechanisms are convergent, however, you only need to suppose that the two groups evolved it independently. Its a question of parsimony - its more simple and therefore more likely that two groups (groups being any useful division) evolved it independently than all the groups of the mollusc family that share a common ancestor with both cephalopods and sea hares lost it independently. Algebraically: if X is the number of 'groups' of molluscs, then 2 < X-2 and assuming that 2 groups have changed is the more parsimonious supposition. There´s a much clearer explanation of this somewhere in the works of Dawkins, but the parsimony article should help. K-22-22 (talk) 06:02, 3 March 2009 (UTC)

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