The colourful "eyespots" on the wings of some butterfly species have been found to address fundamental questions about evolution, including Aristotle's famous "chicken or the egg".
After consideration, Aristotle decided that both the egg and the chicken had always existed. That was not the right answer. The new Oregon State University research is providing a little more detail.
The study, published today in Proceedings of the Royal Society B
, actually attempts to explain the existence of what scientists call "serial homologues," or patterns in nature that are repetitive, serve a function and are so important they are often retained through millions of years and across vast numbers of species.
Repeated vertebra that form a spinal column, rows of teeth, and groups of eyespots on butterfly wings are all examples of serial homologues. Researchers have tracked the similarities and changes of these serial features through much time and many species, but it's remained a question about how they originally evolved.
Put another way, it's easier to see how one breed of chicken evolved into a different breed of chicken, rather than where chickens - or their eggs - came from to begin with.
Butterfly wings are helping to answer that question. These eyespots, common to the butterfly family Nymphalidae
, now serve many butterflies in dual roles of both predator avoidance and mate identification. One theory of their origin is that they evolved from simpler, single spots; another theory is that they evolved from a "band" of color which later separated into spots.
"What we basically conclude is that neither of the existing theories about butterfly eyespots is correct," said Jeffrey Oliver, a postdoctoral scholar in the Department of Integrative Biology of the OSU College of Science. "The evidence suggests that a few eyespots evolved as a group at about the same time, but behaved somewhat as individual entities."
Having appeared as a result of some genetic mutation, however, the eyespots then had the capability to move, acquire a function that had evolutionary value, and because of that value were retained by future generations of butterflies. And at all times, they retained the biological capacity for positional awareness - the eyespots formed in the same place until a new mutation came along.