The new studies overturn decades-old dogma, by showing that spiders that weave orb-shaped webs are not all close kin, with some species more related to species that catch prey differently.
“They are awesome, spider webs — they’re just not the pinnacle of spider evolution that we thought,” says Jason Bond, an evolutionary biologist at Auburn University in Alabama, whose team determined the evolutionary relationship of spiders by analysing more than 300 genes in 33 families. The paper and a similar study from an independent team are both published this week in Current Biology.
The inevitable question:
But why would a spider give up orb-weaving? “Evolution is unpredictable,” responds Matja Kuntner, an evolutionary biologist at the Slovenian Academy of Sciences and Arts in Ljubljana. “A symmetric orb is pretty, but it may only be the ideal architecture in a subset of environments and for a subset of prey the spiders are after.”
Fair enough, but there is something else to note here. It is much easier to shed a complex behaviour like orb-weaving for a simpler behaviour (like lying in wait or stalking) than it would be to invent a new similarly complex behaviour.
There are numerous instances of life forms shedding complex behaviour. Michael Denton has pointed to the many flightless birds of Australia and New Zealand. Of course, some such species then became extinct on the arrival of predators. It might be best to see the complex behaviour as the best package of options for the life form. But how the package was assembled is an open question.
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