Do animals evolve to become bigger and bigger over time? The largest fossilized animal in the Cambrian explosion was the trilobite, dated at 542 million years and topping out at about a foot-and-a-half in length. Can the evolutionary advantages of being bigger explain how the world's largest animal — the blue whale — evolved to be 100,000 times larger than the largest trilobite? Stanford University evolutionary scientists answer "yes" to both of these questions, at least for marine animals. Stanford paleobiologist Jonathan Payne and colleagues base their conclusions on a statistical survey of the body sizes of over 17,000 kinds of animals. His team reports that the average size of marine animals increased more than 150-fold over the past 542 million years. Most of the size increase, statistically speaking, was due to an increase in the maximum size of fossils in each layer ascending from the Cambrian through the Pleistocene strata. In other words, among the marine animals surveyed, the largest animals in each fossil layer were larger than the largest in the layers below. If the fossil layers actually did represent an evolutionary timeline, then this might suggest that the record-breaking sizes marine animals could achieve got larger and larger over millions of years. (As we will point out below, the layers do not mark millions of years of elapsed time, and there is another explanation for the way these fossils stack up!)
Matching the Model
The Stanford researchers tried to determine whether evolutionary advantages led to the average size increase of marine animals ascending in the fossil record. "It's possible that as evolution proceeds, there really is no preference for being larger or smaller," the study's lead author Noel Heim explains. "What appears to be an increase in average body size may be due to neutral drift [random non-selective changes]." Therefore, they compared their collected data to a computer model of how evolution presumably should have happened if "survival of the fittest" really were a decisive boon to upscaled body size over millions of years.
[Read the rest of the article at Answers in Genesis.]