Studies on the origin of life on Earth seem to point to the fact that the first complex creatures developed around the Equator, hundreds of millions of years ago. As they evolved, their range expanded, and migrations eventually led the animals to all corners of the world. And while they adapted to cooler temperatures and learned to live in the freezing waters of the poles, creatures living at high latitudes were still fewer than the abundance of species that could be met near the Equator.

Scientists have been able to determine that this trend in the spread of animals across the surface of the planet dates back to the very beginning of species. For example, the latitudinal diversity gradient (LDG) measures the number of plant and animal species that live on each degree of latitude. It reaches its peak at the starting point – in areas around the Equator – and then gradually decreases as it approaches the poles. University of Chicago (UC) researcher Andrew Krug says that, “The gradient is pretty dramatic for almost everything.”

The study seeking to understand the LDG, authored by Krug and colleagues David Jablonski, James Valentine and Kaustuv Roy, will soon be published in an issue of the Astrobiology Journal. The goal of the research is to understand what a planet may need in order to allow for life to appear and flourish. Understanding how the gradient modifies with time and distance could set the basis for future terraforming processes, or may give astronomers a clue of where to start looking for life on other planets, with teams of robotic probes able to take good care of themselves, without human interference.

Since the existence of the LDG was first hinted at, more than 200 years ago, naturalists, evolutionists and biologists have been trying to make sense of it, and a very large array of explanations has been set forth to unveil its mechanisms. The main issue with revealing how it functions is the fact that life is seemingly able to occupy every possible niche on the planet's surface, including volcano craters, hydrothermal vents, and solid rocks.

“We've still not converged on a solution,” Krug explains, adding that the potential answers to this riddle cover a very wide range of explanations. Geography, tectonic plates, the temperatures and the weather patterns may have all played a role in the distribution of species across the planet. Some even maintain that species living at the poles chose to do so all those years ago because they had more room than at the Equator. “It may tell us how we went from the origins of life to the vast biodiversity that we have today,” the expert concludes.