How can modern experiments test hypotheses about the evolutionary impact of ancient environmental changes?

Several experiments have been conducted to test the link between O₂ concentrations and evolution of body size in flying insects (one of these is discussed in Investigating Life: The Relationship between Atmospheric Oxygen Concentration and Body Size in Insects). Results of these experiments are consistent with the evolution of larger body size in flying insects in hyperoxic (high-oxygen) environments. Experiments have also been conducted under hypoxic (low-oxygen) conditions, such as existed at the end of the Permian. Results of these experiments suggest that the evolution of body size is constrained under hypoxic conditions, even under strong artificial selection for larger body size. These latter results are consistent with the extinction of many of the large flying insects at the end of the Permian, the result of rapidly decreasing O₂ concentrations. Giant flying insects simply could not have survived the lower O₂ concentrations that existed at that time. The mass extinction at the end of the Permian is the only known mass extinction that involved considerable loss of insect diversity.

Future directions

Experiments with living organisms are providing information about how quickly various groups of organisms evolve. They also inform us about the factors involved in extinction of species (as in the example in Figure 24.10). As human activities affect the climate of Earth, experimental approaches will be important to help us predict how our actions may affect future directions of evolution and extinction.