External appearance, it turns out, is not a good way to identify relationships between species, especially more distant relationships. And even internal anatomical structure isn’t so good either. Studies of genomes at the molecular level are more reliable. In the latest example, it’s been found that snails and octopuses do not seem to be as closely related as previously believed, even though the two cephalopods both have relatively complex nervous systems (compared to other molluscs such as clams).
Examination of the genomes can also provide estimates of how much time elapsed since different species shared a common ancestor. Based on this, it appears that the nervous systems of snails and octopuses developed their complexity independently, as probably happened also in two other less familiar types of mollusc.
Slimy and often sluggish they may be, but some molluscs deserve credit for their brains – which, it now appears, they managed to evolve independently, four times.
The mollusc family includes the most intelligent invertebrates on the planet: octopuses, squid and cuttlefish. Now, the latest and most sophisticated genetic analysis of their evolutionary history overturns our previous understanding of how they got so brainy.
The new findings expand a growing body of evidence that in very different groups of animals – molluscs and mammals, for instance – central nervous systems evolved not once, but several times, in parallel.