HamsterZerg wrote:Why would an insect have four legs as a typical phenotype?
For whatever reason that family has the front pair reduced to small brush-like structures (hence the name 'brush-footed butterflies'), but I've never seen any theories for what purpose they serve. Whatever it is, though, it clearly works, as it is a numerous and wide-spread family.
I noticed that the red butterfly did only have four legs. but I didn't want to mention it on the off chance that the legs simply broke off, while struggling. interesting to note that it is a family feature though.
To answer the above questions evolution happens in all directions, because it's a function of mutation. Mutations could've simply degenerated the front legs through random chance and since it didn't hinder the insect very much it ended up evolving in the population.
the most typical answer is that because the insect evolved the degenerated legs feature, it conserved more energy than it's six legged ancestor. The insect doesn't have to grow the cells for legs and instead can focus more energy into producing eggs. Alternatively it also weighs slightly less so conserves energy for flying.
I want to point out that one of the most successful insect clades is diptera, the flies. and they lost their back wings, reducing them down to small structures called Halteres. And they also lost those tough chewing mandibles that you see in wasps. And Flies are one of the most diverse families of insect.
Generally if there is no pressure to retain a feature, a species slowly loses it over-time due to mutation. You'll see this happen to organisms that live in dark low energy caves, they lose wings, pigmentation, sight, etc etc. If those features aren't useful in the environment generally the higher fecundity organisms win out.
Incase you want to do some reading on this topic yourself. Heres a scientific article Cited 158 times that talks about the evolution of flightlessness in birds. https://www.researchgate.net/profile/Br ... 040430.pdf