The ancestors of today's insects first emerged on dry land more than 400 million years ago, and they had the place to themselves for quite a long time. Various vertebrates wouldn't crawl out of the sea until about 50 million years later, says David A. Grimaldi, author of "Evolution of the Insects." Eventually, these bugs evolved into some 5 millions species [source: Zimmer].
How did such small invertebrates manage to thrive when usually outsized? Sometimes small size is an asset -- it comes in handy when hiding, for example. But flight may have been their most helpful evolutionary feature. The oldest known fossil (the one dated about 400 million years ago) likely had wings, so fossil records hold no clues about how insects first added these handy appendages. In 2010, a Japanese research team reported on its study of mayflies and wingless bristletail insects, relatives of the silverfish [source: Vergano]. Both of these insects have genes similar to those of the earliest known bugs. They looked at genes in the insects' eggs to test two theories of wing development. One of these says that wings are new features arising from insects' back shells. The other proposes that wings are modified extensions of insects' legs. The research team found that it looks like both theories are partially correct: Two genes work together to develop wings in mayfly embryos but do nothing at all in developing silverfish.
The researchers' discovery may have been important to those who study insect history and collect bugs but also helped to understand theories of evolutionary biology. Today, insects (and other invertebrates) are fundamentally important to life on Earth. The millions of insect species account for more than all other types of animals put together -- and their biomass is similarly amazing. Added together, they would outweigh all other animals on the planet combined. But just as insects could not have evolved so successfully without plant life, many animals depend on insects for their survival. And although we may detest the pests that buzz around our homes, picnics or crops, Grimaldi and others emphasize that it's important to protect as many of the millions of insect species as possible.
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