All living things must survive in environments that are constantly changing. Seasons shift from summer to winter, and weather patterns can swing from floods one year to drought the next. Populations of plants and animals are always dealing with new pressures, explains University of Vermont scientist Csenge Petak. What remains unclear is how this ongoing instability shapes evolution over time.

Petak wondered whether frequent environmental changes actually help populations adapt by preparing them for future challenges, or whether constant disruption slows progress. "Do populations benefit from lots of environmental fluctuations, making new generations more prepared to face future changes," she asked, "or are they impaired, forced to readapt again and again, never reaching the heights of fitness that the same populations in a stable environment could achieve?"

Simulating Evolution Across Generations

To investigate this question, Petak teamed up with University of Vermont computer scientist Lapo Frati, along with two other UVM researchers and a collaborator from the University of Cambridge. Together, they designed a groundbreaking study using advanced computer simulations that followed thousands of generations of digital organisms.

The findings, published December 15 in the Proceedings of the National Academy of Sciences (PNAS), challenged simple assumptions about evolution. "We found remarkable variation in how populations evolved in variable environments," the researchers reported. "In some cases, changing the environment helped populations find higher fitness peaks; in others, it hindered them."

Impossible to Test in a Lab

Traditional evolutionary research often tracks a single population living under one set of conditions. Frati explains that this narrow focus can miss important patterns. "Researchers often watch the long-term trajectory of one population in a specific environment, says Frati. "We picked an array of environments and see how the specifics of each one influence the trajectory of many populations."

To see why this broader approach matters, consider fruit flies living in very different parts of the world. A population in the United States might experience seasonal temperature swings, while another in Kenya alternates between long dry spells and heavy rainfall. These groups belong to the same species, yet they face very different challenges.

"Temperature fluctuations might promote better adaptation to both cold and warm seasons," Petak explains. "But repeated cycling between dry and wet seasons might actually impede adaptation to drought, forcing the population to 'restart' evolution after they experience a long period of rainfall -- leading to worse traits than in populations exposed only to drought." As a result, one population may benefit from environmental shifts while another is held back by them.