A new study led by Adelaide researchers has estimated, for the first time, the rates of evolution during the "Cambrian explosion" when most modern animal groups appeared between 540 and 520 million years ago. The findings, published online today in the journal Current Biology, resolve "Darwin's dilemma": the sudden appearance of a plethora¹ of modern animal groups in the fossil record during the early Cambrian period.

 

"The abrupt² appearance of dozens of animal groups during this time is arguably the most important evolutionary³ event after the origin of life," says lead author Associate Professor Michael Lee of the University of Adelaide's School of Earth and Environmental Sciences and the South Australian Museum.

 

"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 odds⁴ with the normal evolutionary processes.

 

"However, because of the notorious imperfection of the ancient fossil record, no-one has been able to accurately⁵ measure rates of evolution during this critical interval⁶, often called evolution's Big Bang.

 

"In this study we've estimated that rates of both morphological and genetic⁷ evolution during the Cambrian explosion were five times faster than today -- quite rapid, but perfectly⁸ consistent with Darwin's theory of evolution."

 

The team, including researchers from the Natural History Museum in London, quantified the anatomical and genetic differences between living animals, and established a timeframe over which those differences accumulated with the help of the fossil record and intricate（复杂的） mathematical models. Their modelling showed that moderately accelerated evolution was sufficient to explain the seemingly sudden appearance of many groups of advanced animals in the fossil record during the Cambrian explosion.

 

The research focused on arthropods（节肢动物） (insects, crustaceans⁹甲壳类, arachnids蛛形类 and their relatives), which are the most diverse animal group in both the Cambrian period and present day.

 

"It was during this Cambrian period that many of the most familiar traits associated with this group of animals evolved, like a hard exoskeleton, jointed¹⁰ legs, and compound (multi-faceted) eyes that are shared by all arthropods. We even find the first appearance in the fossil record of the antenna¹¹ that insects, millipedes and lobsters¹² all have, and the earliest biting jaws¹³." says co-author Dr Greg Edgecombe of the Natural History Museum.

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