Which animal evolves the fastest?

Evolution occurs over millennia, but it can also occur in just a few generations. For example, Darwin’s finches in the Galapagos rapidly evolved specialized beaks as food choices changed, and Carolina lizards (Anolis carolinensis) evolved larger toe pads that allowed them to climb high to escape predators, and the birch butterfly (Biston betularia) turned dark as the Industrial Revolution polluted cities with soot. However, researchers are still divided on which vertebrate evolved the fastest, according to Live Science.

Michael Benton, a vertebrate paleontologist in Bristol, UK, says there are two main aspects to consider. “One is that there is an innate element in living organisms that causes some to evolve rapidly while others evolve slowly. The other is that all living organisms can evolve rapidly, but it depends on changes in the environment,” Benton says.

The title of fastest evolving species is therefore controversial. Some scientists believe that title belongs to the tuatara (Sphenodon punctatus), a lizard-like creature found only in modern-day New Zealand. This reptile is the sole survivor of the Rhynchocephalia order, which was much more diverse during the Mesozoic Era (66 – 251.9 million years ago) than the Squamata, the modern order of lizards and snakes.

A 2008 study in the journal Trends in Genetics analyzed the DNA of ancient and modern tuatara and found that this living fossil has the fastest rate of molecular evolution ever recorded in a vertebrate. This means that although their external appearance has remained largely unchanged for millions of years, tuatara have rapidly evolving DNA. Similarly, scientists have found that Adélie penguins (Pygoscelis adeliae) evolved 2-7 times faster than previously estimated genetically, even though their appearance changed very little.

But not all scientists agree that evolution at the genetic level makes tuatara the fastest-evolving species. In fact, they don’t seem to have evolved much anatomically, given that they’ve been perfectly suited to New Zealand for as long as they’ve lived there, says Michael Lee, an evolutionary biologist at Flinders University and the South Australian Museum.

Instead, Lee argues that the Lake Victoria cichlid is the fastest-evolving vertebrate. Lake Victoria is Africa’s largest and newest lake, spanning Uganda, Tanzania, and Kenya. More than 500 species of cichlids have evolved there in the past 15,000 years, a relatively short time for adaptive radiation to occur. That’s when one species rapidly diverges into many different species. “They don’t just split into new species, they also change their appearance to fit into different areas of their environment,” Lee says.

For example, some species feed on plankton higher in the water column while others forage for larvae at the muddy bottom of lakes. The ability to inhabit specialized areas of their ecosystems partly explains how they evolved into so many species. Their second pair of jaws, located further back in their throats, allows cichlids to eat different types of prey more flexibly. A second reason is that cichlids are selective and can reproduce rapidly. By selectively reproducing only with individuals with similar traits, they can create distinct species over a few generations. The different species then interbreed, creating hybrids.

In addition to the cichlid, the guppies (Poecilia reticulata) are another candidate, according to James Stroud, an evolutionary biologist at the Georgia Institute of Technology. Research shows that guppies in a predator-free tributary of Trinidad evolved at a rate of 3,700 to 45,000 darwins, a unit of measurement used to standardize evolutionary rates, much faster than the 200,000 darwins that mice can achieve through artificial selection.