Many researchers have thought new species evolve in tandem with the development of different physical characteristics and the appearance of new kinds of habitats. In this scenario, these three factors feed into one another, potentially leading to a dramatic increase in the number of new species. This burst of diversification eventually tapers off as species compete with one another in an increasingly crowded environment, much like a saturated market. This hypothesis has held true in several studies of tropical organisms, but a new study uncovered a very different pattern in temperate species, organisms that live in areas with warm summers and cold winters. When researchers examined the evolution of a large lineage of flowering plants known as Saxifragales, they found that species diversified first, driven by the Earth's cooling climate 15 million years ago. These plants invaded new habitats and evolved new physical traits, too, but not until about 5 million years later. Shown here: Micranthes atrata, which lives in the alpine tundra of the Tibetan Plateau in Central and East China. Tens of millions of years ago, plants in the order Saxifragales were extreme specialists, inhabiting the few cold regions on a more tropical Earth until a cooling climate opened new habitats.
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