The Great Replacement

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Bronze cuckoos annoy other birds.

Too lazy, perhaps, to build their own nests, they lay their eggs in the carefully constructed homes of small songbirds. When the cuckoo egg hatches, the chick then pushes the host bird’s eggs out of the nest and tricks the new parents into caring for it.

They are nature’s ultimate free-loaders.

More amazing still is what happens next, the so-called coevolution – and possibly the creation of a new species – in a process called speciation, which happens after the close interaction between species, according to a new study that resulted from two decades of observation and analysis by a team of scientists.

Scientists call it “an evolutionary arms race.” The prize? More species.

“This finding is significant in evolutionary biology,” said Clare Holleley, an evolutionary biologist at the Australian National Wildlife Collection, who worked on the study. “It shows that coevolution between interacting species increases biodiversity.”

Until now, there hadn’t been any evidence to support this theory.

To prove it, the researchers used scientific modeling, and “looked at the DNA and morphology of bronze cuckoos,” wrote Corinne Simonti, editor of the journal Science where the study was published.

They found that speciation was more likely when a cuckoo species targets several different host species.

“Cuckoos are very costly to their hosts, so hosts have evolved the ability to recognize and eject cuckoo chicks from their nests,” said Naomi Langmore of Australian National University, Canberra, lead author of the study.

To avoid this, cuckoo chicks mimic the hosts’ chicks’ appearance and birdsong, thus going into separate genetic lineages.

“This exciting new finding could potentially apply to any pairs of species that are in battle with each other,” said co-author Rebecca Kilner of Cambridge University’s Department of Zoology. “Just as we’ve seen with the cuckoo, the coevolutionary arms race could cause new species to emerge – and increase biodiversity on our planet.”