Biodiversity of a coral reef
Life on earth is comprised of over 8.5m species of which hardly a million have been catalogued. Wikimedia Commons

Contrary to popular belief, the tree of life on Earth is alive and kicking, and diversification of species has not slowed down.

Temple University researchers have assembled the largest and the most accurate tree of life to date and it reveals that life has been expanding at a constant rate.

"The constant rate of diversification that we have found indicates that the ecological niches of life are not being filled up and saturated," said Temple professor S Blair Hedges, a member of the research team's study, published in the early online edition of the journal Molecular Biology And Evolution.

The Timetree of Life initiative (TTOL) led by the team hopes to discover when each species and all its ancestors originated, right back to the origin of life some four billion years ago.

The tree of life compiled to resemble a cosmologically-inspired galaxy of life view contains more than 50,000 species in the tapestry of life on the planet.

Rather than adaptation dictating species diversification, the tree underscores the importance of random genetic events and geographic isolation in the process, with two million years on average required for a new species to emerge onto the scene.

"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."

The Timetree of Life throws fresh evolutionary perspective on studies of disease and medicine, and the effect of climate change on future species diversity.

Data from 2,274 molecular studies, with a majority published in the last decade, was used to compile the tree. New computer algorithms and tools were used to synthesise the largest collection of evolutionary species diversity timelines published to date.

Researchers around the world estimate species divergence times by looking at DNA mutational rates and species divergence times obtained from genome sequences.

Combined with the fossil record and geological history, a constantly improving view of diversity of life has been obtained.

Hedges and colleagues plan to continue adding new data to TTOL from future studies. They also hope to improve data access and exploration of the TTOL.

In the last census of life on earth conducted in 2011, around 8.7m species were calculated using statistical approximations and that excluded bacteria and small organisms. Scientists have catalogued approximately 1.5 million species.

The International Union for the Conservation of Nature has assessed only 59,508 species, of which 19,625 are classified as threatened.

Around 86% of all land-dwelling species and 91% in the water have yet to be discovered and catalogued by science, according to an estimate published in PLoS Biology by the Census of Marine Life scientists.

Many species may disappear before they are even discovered.

Species diversity is a measure of the diversity within an ecological community that incorporates both species richness (the number of species in a community) and the evenness of species' abundances.