Biologists love a good family tree. Mapping the relations between species since the beginning of time is an important aspect of researching the history of evolution. However, classifying and visualizing the links between the millions of species of fauna in the world is no easy task.
Temple University researchers recently put together the world’s largest tree of life visualized across time. The family tree of living and extinct organisms encompasses 50,000 species–only a fraction of the world’s history of life–and would easily take up hundreds of pages if laid out linearly. To fit their work onto a printed page, the researchers, led by evolutionary biologist S. Blair Hedges, instead decided to visualize the data as a spiral.
The spiral strip represents time from top to bottom in greyscale, from the origin of life 4 billion years ago (the darkest gray) to today. Different orders of species of plants and animals (like caryophyllales, a family that includes cacti, or malacostraca, a class of crustaceans) are represented by different colored branches that are connected like a tightly packed family tree.
“Since there are at least 2 million species that have been named, and maybe 10 million out there,” Hedges explains in a phone interview, the project presented a design challenge. A previous visualization that showed branches of species radiating out from the center of a circle only fit 1,600 species. With 50,000 species drawn from 2,300 scientific studies, “there was no way we could do a circular tree,” he explains. On the web, scientists can create infinitely large trees of life (and they are working on that). But it’s harder to create an infographic that can be seen at a glance.
Being able to visualize the evolutionary history of these species, even if they only represent a fraction of all species, was a vital first step toward the group’s research, published in the journal Molecular Biology and Evolution. The spiral tree allowed the biologists to discover that species are splitting off from each other at a constant rate. “A lot of people thought the rate of speciation or diversification was slowing down,” Hedges explains, but his team found that new species are created about every 2 million years.