Charles Darwin famously marveled at the “endless forms, the most beautiful and wonderful” produced by evolution, and indeed, Soil today is full of a an estimated 1 trillion species. But how long did it take for those species to evolve?
The answer varies widely between life forms, “depending on taxa [type of creature] and environmental conditions,” Thomas Smith, a professor of ecology and evolutionary biology at the University of California, Los Angeles, Gadgetmasti told Gadgetmasti. It ranges from human-observable timescales to tens of millions of years.
Crucial, because evolution happens via inherited changes, a creature’s reproductive rate, or generation time, limits the rate at which new species can form – known as speciation rate – according to the University of California, Santa Barbara (opens in new tab) (UCSB). For example because bacteria reproduce so fast, “split[ing] in two every few minutes or hours,” they can evolve into new varieties in years or even days, according to the American Natural History Museum (opens in new tab) in New York City.
However, it can be tricky to determine which bacterial varieties count as new species, Smith said. While scientists delineate species by whether they can interbreed, bacteria do not reproduce sexually. Nevertheless, a 2008 study in the journal Proceedings of the National Academy of Sciences (opens in new tab) reported that a lineage of E coli (opens in new tab) bacteria observed for decades had developed the ability to use citrate as a food source in an oxygen-rich environment. Because the inability to do so “is a defining characteristic of” E coli as a species,” the change could be the start of a new species, researchers said — one that evolved within a few years.
Related: How long do most species take to become extinct?
Plants, in a phenomenon known as polyploidy, can duplicate their entire genomes in seeds, resulting in extra copies of each chromosome and a new species in one generation. The resulting reproductive isolation “automatically creates a new species,” Smith said.
And because many plants reproduce themselves, the new, polyploid organism can continue to create more of the new species. “Plants are often self-fertile, so it can then start an entire population,” UCSB said.
Even in the animal kingdom, speciation can occur on human-observable timescales, particularly in fast-growing insects. apple flies (Rhagoletis pomonella), for example, historically fed on hawthorn plants, but some moved to domesticated apples after they arrived in the northeastern US in the mid-1800s. Since then, the two groups have become reproductively isolated, according to a 2006 study in the journal Annals of the Entomological Society of America (opens in new tab)and are now considered “guest strains” – the first step in a kind of speciation without physical barriers.
Speciation is generally slower in vertebrates, but can still happen quickly. A 2017 study in the journal Science (opens in new tab) reported that a Galapagos finch immigrated to a new island and bred with a native bird there, producing a new reproductively isolated lineage within three generations. That lineage may represent the very rapid initiation of speciation via species hybridization, rather than the slower accumulation of adaptations, study co-author Leif Andersson, a geneticist at Uppsala University in Sweden, told Gadgetmasti.
“This is one possible scenario of how a new species might form,” Andersson said. “But how stable it is over a longer period of time is more uncertain.”
The speed record for complete speciation among vertebrates likely belongs to cichlid fish in Lake Victoria in Africa, Smith said. These fish exploded into 300 species “from a single founder less than 12,000 years ago,” he said. Some studies, such as a 2000 study in the journal Proceedings of the Royal Society B (opens in new tab)has questioned that timeline, but cichlid speciation “is extraordinary,” Smith said.
To find an upper bound for speciation times, look at speciation that occurs because of physical barriers, Smith said. For example, boas, which are mainly found in the Americas, and pythons, which are native to Africa and Asia, differentiated after South America split from Africa. This likely represents tens of millions to 100 million years from continental division to complete speciation, Smith said. (The last common ancestor of these snakes slithered about 70 million years ago during the dinosaur eraaccording to National University of Australia (opens in new tab)while Africa and South America are at about 140 million years ago.)
Naming an average or most common speciation time is challenging, Andersson said, but scientists can estimate the most recent ancestors, giving a rough idea. “In birds and mammals, we usually see … a split between well-developed species is about a million years old,” he said.
A 2015 study in the journal Molecular biology and evolution (opens in new tab) gave a different estimate. Based on data from more than 50,000 species (although this included few bacteria), the researchers found that speciation generally requires the accumulation of mutations over 2 million years. This was true of vertebrates, arthropods (a group that includes insects, arachnids and crustaceans) and plants.
However, such models require many assumptions, warned other researchers in a Quanta Magazine (opens in new tab) story about the investigation. Scientists are on a more solid footing regarding the factors that slow or accelerate speciation in general — namely, environmental pressures and reproductive isolation, Smith said. “Across all species … the greater the selection pressure and the less gene flow, the more likely you are to get speciation,” he said.
Originally published on Gadgetmasti.