Evolution: factors for speed of diversification (Introduction)

by David Turell , Thursday, August 15, 2019, 22:13 (1715 days ago) @ David Turell

There are several factors that allow for faster changes:

https://phys.org/news/2019-08-early-species-faster-previously-thought.html

"When Earth's species were rapidly diversifying nearly 500 million years ago, that evolution was driven by complex factors including global cooling, more oxygen in the atmosphere, and more nutrients in the oceans. But it took a combination of many global environmental and tectonic changes occurring simultaneously and combining like building blocks to produce rapid diversification into new species, according to a new study by Dr. Alycia Stigall, Professor of Geological Sciences at Ohio University.

"She and fellow researchers have narrowed in a specific time during an era known as the Ordovician Radiation, showing that new species actually developed rapidly during a much shorter time frame than previously thought. The Great Biodiversification Event where many new species developed, they argue, happened during the Darriwilian Stage about 465 million years ago.

"New datasets have allowed them to show that what previously looked like species development widespread over time and geography was actually a diversification pulse.Picture a world before the continents as we know them, when most of the land mass was south of the equator, with only small continents and islands in the vast oceans above the tropics. Then picture ice caps forming over the southern pole. As the ice caps form, the ocean recedes and local, isolated environments form around islands and in seas perched atop continents. In those shallow marine environments, new species develop.

"Then picture the ice caps melting and the oceans rising again, with those new species riding the waves of global diversification to populate new regions. The cycle then repeats producing waves of new species and new dispersals.

"The early evolution of animal life on Earth is a complex and fascinating subject. The Cambrian Explosion (between about 540 to 510 million years ago) produced a stunning array of body plans, but very few separate species of each, notes Stigall. But nearly 40 million years later, during the Ordovician Period, this situation changed, with a rapid radiation of species and genera during the Great Ordovician Biodiversification Event.

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"In their paper, Stigall and colleagues demonstrate that the main pulse of diversification during the GOBE is temporally restricted and occurred in the Middle Ordovician Darriwilian Stage (about 465 million years ago). Many changes to the physical earth system, including oceanic cooling, increased nutrient availability, and increased atmospheric oxygen accumulate in the interval leading up to the Darriwilian.

"These physical changes were necessary building blocks, but on their own were not enough to light the spark of diversification.

"The missing ingredient was a method to alternately connect and isolate populations of species through cycles of vicariance and dispersal. That spark finally occurs in the Darriwilian Stage when ice caps form over the south pole of the Ordovician Earth. The waxing and waning of these ice sheets caused sea level to rise and fall (similar to the Pleistocene), which provided the alternate connection and disconnection needed to facilitate rapid diversity accumulation."

Comment: All of these factors allowed the diversification to occur in a speedy fashion but it must be remembered, the genome must initiate change and that is the driving factor, n ot the environment.