For millions of years, large size conferred advantages in ecological dominance for many species. However, this very size ultimately proved to be a disadvantage as environments changed and extinction events occurred. Larger creatures are inherently more vulnerable to environmental shifts and mass extinctions due to factors like slower reproduction rates and greater resource needs. The rise of humans and associated hunting pressures further contributed to the decline of megafauna. The text suggests a correlation between large body size and increased susceptibility to extinction throughout evolutionary history. Essentially, while once beneficial, being large became a liability in a changing world. This explains the absence of giant creatures in modern ecosystems.