Asked by: Alain Bertrand, by email
Insects are arthropods and the basic arthropod body type is to have bilaterally symmetrical body segments with a pair of legs on each one. Segments on the most primitive arthropods tended to perform the same functions, but more recent lineages have fused many of the segments together and dedicated those that remain to certain roles. There are some extinct insects (such as the Palaeodictyoptera) that had six wings, but these probably weren’t terribly effective fliers. The four-wing model is the first to really crack the problem of flight, and insects that look essentially like modern dragonflies are present in the fossil record at least as far back as 320 million years ago. Some insect orders have subsequently evolved one of their pairs of wings into a protective cover (such as beetles) or reduced them to tiny vestigial balance organs, as in the case of true flies.