JOIN USResearchers, including one of Indian-origin, have assembled the largest and most accurate tree of life calibrated to time, showing that life has been expanding at a constant rate.
The tree of life compiled by the team is depicted in a new way - a cosmologically-inspired galaxy of life view - and contains more than 50,000 species in a tapestry spiralling out from the origin of life.
"The constant rate of diversification that we have found indicates that the ecological niches of life are not being filled up and saturated," said Professor S Blair Hedges from Temple University.
"This is contrary to the popular alternative model which predicts a slowing down of diversification as niches fill up with species," said Hedges.
For the massive meta-study effort, researchers painstakingly assembled data from 2,274 molecular studies, with 96 per cent published in the last decade.
They built new computer algorithms and tools to synthesise this largest collection of evolutionary peer-reviewed species diversity timelines published to date to produce this Time Tree of Life.
The study also challenges the conventional view of adaptation being the principal force driving species diversification, but rather, underscores the importance of random genetic events and geographic isolation in speciation, taking about 2 million years on average for a new species to emerge onto the scene.
These new results add to the decade-long efforts of the Timetree of Life initiative (TTOL), which includes internet tools and a book, led by team members Hedges and Sudhir Kumar.
"This finding shows that speciation is more clock-like than people have thought," said Hedges.
"Taken together, this indicates that speciation and diversification are separate processes from adaptation, responding more to isolation and time.
"Adaptation is definitely occurring, so this does not disagree with Darwinism. But it goes against the popular idea that adaptation drives speciation, and against the related concept of punctuated equilibrium which associates adaptive change with speciation," Hedges added.
Researchers around the world utilise molecular clocks to estimate species divergence times, calculating DNA mutational rates with species divergence times from gene and genomic sequences, that together with the fossil record and geological history, provide a constantly improving view of Darwin's "grandeur of life."
The research was published in the journal Molecular Biology and Evolution.