for National Geographic News
Glance at a crowd at just about any big sporting event and you'll notice that humans are a diverse bunch. Not only the fittest have survived.
Natural selection depends as much on behavior and environmental conditions as it does on physical prowess, as demonstrated by two studies of lizards in tomorrow's issue of the journal Nature.
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"People have a very simple view of how natural selection shapes traits," said Barry Sinervo, an evolutionary biologist who was not involved in the studies. A biologist at the University of California, Santa Cruz, Sinervo said the studies demonstrate the complexity of evolution.
"When behavior or physiology complicates what traits are involved, the results of natural selection are often thwarted or attenuated when compared to our naive perspective," he added.
In one study biologist Jean-Francois Le Galliard and colleagues show how environmental conditions like the abundance of food govern which traits evolve.
Based at the Centre for Ecological and Evolutionary Synthesis at the University of Oslo in Norway, Le Galliard's team found that in food-rich environments, physical prowess is of little advantage to lizard survival. But in environments with scarce food, lizards with high endurance had a better chance of making it to adulthood.
In the other study biologist Jonathan Losos and colleagues shed light on the unpredictable role of behavior in shaping the course of evolution.
"Animals are incredibly dynamic organisms, and the interplay between behavior and environmental change is a complex one which will be hard to predict without extensive knowledge of the organism," said Losos, who teaches at Washington University in St. Louis, Missouri.
Le Galliard and his colleagues wanted to understand why several species, including humans, have a wide range of running abilities, even though the theory of natural selection suggests that weak runners ought to be weeded out from the gene pool.
Le Galliard's team compared the running abilities of the common lizard (Lacerta vivipara) from environments with both ample and limited food supplies. They found that endurance at birth is of little consequence among lizards with plenty to eat, but it is a factor where food is scarce.
In environments where food was ample, lizards that were born with weak endurance caught up with the high-endurance lizards after a few months, the researchers found. In areas of scarce food, though, endurance is often a life-or-death factor.
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