New evidence uncovered by oceanographers challenges one of the most long-standing theories about how species evolve in the oceans. Most scientists believe where different species arise is from an ancestral species only after breeding populations have become physically isolated from each other. This is for both land and sea. The key to this theory is the existence of some kind of physical barrier that restricts interbreeding. Over time such populations diverge until they are considered separate species. Scripps Institution of Oceanography researchers have suggested that this mode of diversification may not be as prevalent for oceanic creatures as it is for land dwellers. What is currently theorized is that the boundaries between regional water masses act as barriers to the movement of plankton that drift in the currents. The existence of these supposed barriers has resulted in the general assumption that these conditions are the dominant cause of plankton diversification throughout the oceans. The new research involving looking at different sediment layers from around the world suggest a different reason. The research indicates that species have come and gone from various areas at times when the Earthâs climate changed. This points to local conditions being a factor in determining weather or not the species can âtake holdâ and thrive. So the idea that different species arise from a parent species without the presence of physical barriers, is more common that previously thought.