Researchers Solve 'Darwin's Dilemma' by Estimating Rate of Evolution during the 'Cambrian Explosion'

The rate of evolution during the Cambrian Explosion was about five times faster than today, which enabled life to jump from simple to complex forms rapidly, researchers from University of Adelaide found.

Life, according to science, sort of exploded during the Cambrian period with many complex organisms suddenly appearing along with basic organisms. But, nobody could explain how life could just blossom so abruptly. University of Adelaide researchers have now solved the long-standing "Darwin's Dilemma" by estimating the rate of evolution between 540 and 520 million years ago- a time known as the "Cambrian Explosion".

"The abrupt appearance of dozens of animal groups during this time is arguably the most important evolutionary event after the origin of life," said Michael Lee of the University of Adelaide's School of Earth and Environmental Sciences and the South Australian Museum and lead author of the study.

"These seemingly impossibly fast rates of evolution implied by this Cambrian explosion have long been exploited by opponents of evolution. Darwin himself famously considered that this was at odds with the normal evolutionary processes," Lee said in a news release.

For about four billion years, earth was inhabited by basic organisms such as bacteria, plankton and multi-celled creatures. But, the beginning of the Cambrian period saw a plethora of living beings emerge in every ecosystem. Some organisms that appeared during early Cambrian period, such as the Ediacaran fauna from Australia, are still a mystery to researchers. Other life forms that appeared later in the period are direct ancestors of many organisms that exist today.

The current study by Michael Lee and colleagues shows that rates of morphological and genetic evolution were roughly five times faster than the current rate of evolution. According to the experts, a moderate increase in rate of evolution explains how life made the jump from simple to complex systems, without contradicting Darwin's theory of evolution.

Note that what researchers call "the ancient fossil record" are creatures that remained preserved in fossil form until scientists dug them out. Experts depend on fossils of tiny creatures that existed during that time, which makes estimation of evolutionary rate extremely difficult.

Also, approximating rates of evolution during the critical Cambrian period is especially difficult as life blossomed quickly, an event often regarded as evolution's Big Bang. Some stages of the biological changes during this period took about 30 million years, others took about 5-10 million years.

"In this study we've estimated that rates of both morphological and genetic evolution during the Cambrian explosion were five times faster than today - quite rapid, but perfectly consistent with Darwin's theory of evolution," Lee said.

The study included researchers from the Natural History Museum in London. The team used fossil records and intricate mathematical models to quantify the anatomical and genetic differences between animals and design a time-frame over which these differences might have occurred.

The research specifically looked at records of insects, crustaceans, arachnids and their cousins. Arthropods have existed since Cambrian period and still exist.

"It was during this Cambrian period that many of the most familiar traits associated with this group of animals evolved, like a hard exoskeleton, jointed legs, and compound (multi-faceted) eyes that are shared by all arthropods. We even find the first appearance in the fossil record of the antenna that insects, millipedes and lobsters all have, and the earliest biting jaws," said Dr Greg Edgecombe of the Natural History Museum and co-author of the study.

The study is published in the journal Current Biology.