Mammal evolution to bigger sizes explained

Researchers from the Arizona State University have put forth a new theory that may help explain why mammals differ in size, despite thousands of years of evolution.

The Earth is a home to mammals of varying sizes ranging from as huge as whales and elephants to as small as other primates. This research, led by Jordan Okie, published in the journal Proceedings of the Royal Society B, has managed to explain the reason behind this fact.

The research team, which consisted of palaeontologists, ecologists and evolutionary biologists looked at the information that helped them evaluate how large an oraganism may grow over the years of the evolutionary time.

Their observation revealed that some animals tended to live for short spans and died young, while some other mammals lived on for years, and take a longer span to mature. With this information, they proposed a theory that mammals who live for shorter spans have a tendency to evolve to a larger size, as compared to the mammals who lived on for years.

The researchers also tested fossil records of mammals who lived for around 70 million years ago and examined the maximum size of the largest mammal during that time.

"Primates have evolved very slowly, and never got bigger than 1,000 pounds," Okie explained. "The opposite was true of whales, which evolved their large size at the fastest rates recorded."

The researchers also explained that since mammals living for longer spans tend to breed less frequently in a fixed time frame, as compared to mammals who live for shorter duration, the rate of evolution for the mammals living for longer life spans would be lesser, as compared to the other mammals.

"This is a really surprising finding," co-author of the study, Alistair Evans, from Monash University. "It points to another reason why many of the large animals went extinct after the last Ice Age, and their high risk of extinction in modern environments."

This study was funded by a Research Coordination Grant from the US National Science Foundation. Further studies may help researchers find how the risk of extinction may be reduced in climate change. 

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