Charles Darwin marveled at the “infinite forms more beautiful and wonderful” produced by evolution and, in fact, Land today is brimming with estimated 1 billion species. But how long did it take for those species to evolve?
The answer varies widely among life forms, “depending on taxa [type of creature] and environmental conditions,” Thomas Smith, professor of ecology and evolution biology at the University of California, Los Angeles, he told LiveScience. It ranges from human-observable timescales to tens of millions of years.
Crucially, because evolution occurs through inherited changes, a creature’s rate of reproduction, or generation time, limits the rate at which new species can form, known as the rate of speciation, according to the University of California, Santa Barbara (opens in a new tab) (UCSB). For example, because bacteria reproduce so quickly, “split[ing] in two every few minutes or hours,” can evolve into new varieties in years or even days, depending on the American Museum of Natural History (opens in a new tab) In New York.
However, determining which bacterial strains count as new species can be tricky, Smith said. While scientists delimit species based on whether they can interbreed, bacteria do not reproduce sexually. However, a 2008 study in the journal Proceedings of the National Academy of Sciences (opens in a new tab) reported that a lineage of E. coli (opens in a new tab) Bacteria observed for decades had evolved the ability to use citrate as a food source in an oxygenated environment. Because the inability to do this is “a defining characteristic of E. coli as a species,” the change could represent the beginning of a new species, the researchers said, one that developed within a few years.
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 on their own, the new polyploid organism can create more new species. “Plants are often self-fertilizing, so they can then start an entire population,” UCSB said.
Even in the animal kingdom, speciation can occur on human-observable timescales, particularly among rapidly generating insects. codling moth flies (Rhagoletis pomonella), for example, historically fed on hawthorn plants, but some were switched to domesticated apples after they arrived in the northeastern US in the mid-19th century. 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 a new tab)and are now considered “host races”, the first step in a type of speciation without physical barriers.
Speciation generally moves more slowly in vertebrates, but can still occur quickly. A 2017 study in the journal Sciences (opens in a new tab) reported that a Galapagos finch migrated to a new island and bred with a native bird, producing a new reproductively isolated lineage within three generations. That lineage may represent the very rapid onset of speciation through species hybridization, rather than the slower accumulation of adaptations, study co-author Leif Andersson, a geneticist at Uppsala University in Sweden, told Live Science. .
“This is a possible scenario for how a new species can form,” Andersson said. “But then 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 Africa’s Lake Victoria, Smith said. These fish exploded into 300 species “from a single founder less than 12,000 years ago,” he said. Some research, such as a 2000 study in the journal Proceedings of the Royal Society B (opens in a new tab)has disputed that timeline, but cichlid speciation “is extraordinary,” Smith said.
To find an upper bound for speciation times, look at speciation that occurs due to physical barriers, Smith said. For example, boas, which are found primarily in the Americas, and pythons, which are native to Africa and Asia, diverged after South America split from Africa. This probably represents tens of millions to 100 million years from the continental divide to full speciation, Smith said. (The last common ancestor of these snakes slithered about 70 million years ago during the age of the dinosaursaccording to Australian National University (opens in a new tab)while Africa and South America are divided into roughly 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, what we see is that normally … a division between well-developed species is about a million years old,” he said.
A 2015 study in the journal Molecular Biology and Evolution (opens in a new tab) gave another estimate. Drawing on data from more than 50,000 species (although this included some bacteria), the researchers found that speciation typically requires the accumulation of mutations over 2 million years. This held true for vertebrates, arthropods (a group that includes insects, arachnids, and crustaceans), and plants.
However, such models require many assumptions, other researchers warned in a how much magazine (opens in a new tab) research story. Scientists have a stronger foundation regarding the factors that slow down or speed up speciation in general, namely environmental pressure and reproductive isolation, Smith said. “In all species … the higher the selection pressure and the lower the gene flow, the more likely you are to get speciation,” he said.
Originally published on Live Science.
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