Scientists seek to crack an evolutionary code.
“Big bang” isn’t just an astronomy term. Biologists use it when describing the rise of life on Earth, too: Dozens of modern animal groups evolved in a relatively short time frame in the early Cambrian period, between 540 million and 520 million years ago. And according to a new Australian study on the subject, this biological “big bang” actually fits quite well with what we already know about the processes of evolution.
This big bang event has perplexed science for over a century. Michael Lee, University of Adelaide biologist and the study’s lead author, noted that researchers in his field call it “Darwin’s Dilemma,” because natural-selection pioneer Charles Darwin had said that the emergence of so many species in so little time seemed to be at odds with evolution as he understood it. Opponents of evolutionary theory have even used this big bang event as evidence for intelligent design or creationism.
But Lee and his colleagues beg to differ. They examined the rates of evolutionary change that occurred during this 20-million-year time period while working with the Natural History Museum in London to map out and analyze the genetic and anatomical differences to be found among today’s myriad animal species.
Then they compared the present-day species diversity with the earlier menagerie of prehistoric life as indicated in the fossil records, and they built mathematical models to connect the two and discern the rate at which the differences would have accumulated. Their final conclusion: Simple evolutionary processes do fully explain the rapid debuting of so many new species in the Cambrian big bang.
The arthropods—which include insects, spiders, and crustaceans, around 80% of Earth’s animal species in total— were the most successful and diverse group of animals to evolve in the Cambrian explosion. So Lee and his colleagues zeroed in on them. The Cambrian big bang witnessed an overall rate of evolution that was four to five times faster than the rate of any other era, including ours.
That sounds huge, but Lee and his colleagues found that it made sense given the changes that arthropods and their environments were going through at the time. Exoskeletons, jointed legs, multifaceted eyes, and the ability to actively swim all first appeared in this time frame. So did antennae and biting jaws.
The researchers noted that the arthropods were breaking into new environments in this time, and all species are more likely to make swift evolutionary changes when they reach new environments. Darwin’s theory of evolution, they conclude, is in no danger of going extinct.