<p>A mouse-sized mammal could turn into a giant beast as big as an elephant in about 24 million generations in the process of evolution, says a new study.<br /><br /></p>.<p>A team of 20 biologists and palaeontologists who for the first time calculated the rate of evolutionary change in mammals discovered that rates of size decrease are much faster than growth rates.<br /><br />For their study, published in the journal Proceedings of the National Academy of Sciences, the team looked at fossils, literature and historical documents to get information of 28 different groups of mammals from various continents and ocean basins over the past 70 million years.<br /><br />It was found that a small mouse-like mammal may evolve into an elephant-like animal in about 24 million generations, but it takes only 100,000 generations for very large decreases, leading to dwarfism, to occur.<br /><br />Lead author Dr Alistair Evans, an evolutionary biologist at Monash University's School of Biological Sciences, said the study was unique because most previous work had focused on microevolution, the small changes that occur within a species.<br /><br />"Instead we concentrated on large-scale changes in body size. We can now show that it took at least 24 million generations to make the proverbial mouse-to-elephant size change, a massive change, but also a very long time," Dr Evans said in a statement.<br /><br />"A less dramatic change, such as rabbit-sized to elephant-sized, takes 10 million generations," he added.<br /><br />According to the researchers, they tracked size change in generations rather than years to allow meaningful comparison between species with differing life spans.<br />Co-author Dr Erich Fitzgerald of Vertebrate Palaeontology at Museum Victoria said changes in size of whale occurred at twice the rate of land mammals. "This is probably because it's easier to be big in the water -- it helps support your weight," Dr Fitzgerald said.<br /><br />Dr Evans said he was surprised to find that decreases in body size occurred more than ten times faster than the increases.<br /><br />"The huge difference in rates for getting smaller and getting bigger is really astounding – we certainly never expected it could happen so fast!" Dr Evans said.<br />Many miniature animals, such as the pygmy mammoth, dwarf hippo and 'hobbit' hominids lived on islands, helping to explain the size reduction.<br /><br />"When you do get smaller, you need less food and can reproduce faster, which are real advantages on small islands," Dr Evans said. The study furthers understanding of conditions that allow certain mammals to thrive and grow bigger and circumstances that slow the pace of increase and potentially contribute to extinction, the researchers added.</p>
<p>A mouse-sized mammal could turn into a giant beast as big as an elephant in about 24 million generations in the process of evolution, says a new study.<br /><br /></p>.<p>A team of 20 biologists and palaeontologists who for the first time calculated the rate of evolutionary change in mammals discovered that rates of size decrease are much faster than growth rates.<br /><br />For their study, published in the journal Proceedings of the National Academy of Sciences, the team looked at fossils, literature and historical documents to get information of 28 different groups of mammals from various continents and ocean basins over the past 70 million years.<br /><br />It was found that a small mouse-like mammal may evolve into an elephant-like animal in about 24 million generations, but it takes only 100,000 generations for very large decreases, leading to dwarfism, to occur.<br /><br />Lead author Dr Alistair Evans, an evolutionary biologist at Monash University's School of Biological Sciences, said the study was unique because most previous work had focused on microevolution, the small changes that occur within a species.<br /><br />"Instead we concentrated on large-scale changes in body size. We can now show that it took at least 24 million generations to make the proverbial mouse-to-elephant size change, a massive change, but also a very long time," Dr Evans said in a statement.<br /><br />"A less dramatic change, such as rabbit-sized to elephant-sized, takes 10 million generations," he added.<br /><br />According to the researchers, they tracked size change in generations rather than years to allow meaningful comparison between species with differing life spans.<br />Co-author Dr Erich Fitzgerald of Vertebrate Palaeontology at Museum Victoria said changes in size of whale occurred at twice the rate of land mammals. "This is probably because it's easier to be big in the water -- it helps support your weight," Dr Fitzgerald said.<br /><br />Dr Evans said he was surprised to find that decreases in body size occurred more than ten times faster than the increases.<br /><br />"The huge difference in rates for getting smaller and getting bigger is really astounding – we certainly never expected it could happen so fast!" Dr Evans said.<br />Many miniature animals, such as the pygmy mammoth, dwarf hippo and 'hobbit' hominids lived on islands, helping to explain the size reduction.<br /><br />"When you do get smaller, you need less food and can reproduce faster, which are real advantages on small islands," Dr Evans said. The study furthers understanding of conditions that allow certain mammals to thrive and grow bigger and circumstances that slow the pace of increase and potentially contribute to extinction, the researchers added.</p>
