A new scientific study has challenged a long-standing idea in evolutionary biology, offering fresh insight into why some groups of organisms rapidly evolve into thousands of species while others remain limited. The research, inspired by questions first raised by Charles Darwin, suggests that the speed of evolutionary change rather than specific traits may be the key driver of biodiversity.
The study, conducted by researchers from the University of Reading, focuses on cacti, one of the most diverse yet threatened plant families in the world. Despite being known for their slow physical growth, cacti have evolved rapidly over millions of years, producing around 1,850 species in just 20 to 35 million years a relatively short period in geological terms.
For decades, scientists believed that specialised traits, particularly flower adaptations linked to specific pollinators like bees, bats, moths, and hummingbirds, were responsible for this rapid diversification. Another theory suggested that the spread of deserts created ideal conditions for cactus evolution.
However, the new findings challenge both ideas. By analysing data from more than 750 cactus species using the newly developed Cactus Ecological Database, researchers discovered that neither pollinator specialisation nor environmental factors like aridity were the primary drivers of species formation.
Instead, the study found that the rate at which flower traits particularly size evolve plays a much more significant role. Cactus flowers vary dramatically, ranging from tiny two-millimetre blooms to large flowers the size of a dinner plate. This variation reflects adaptation to different pollinators, but the crucial factor is not the type of adaptation itself, but how quickly these changes occur over time.
Researchers observed repeated bursts of rapid evolutionary change across the cactus family tree. These bursts allowed species to split and diversify, regardless of whether the flowers became larger or smaller. In simple terms, evolution appears to be driven more by how fast changes happen rather than what those changes are.
This finding could reshape how scientists understand biodiversity across the plant kingdom. It suggests that evolutionary flexibility the ability to adapt quickly may be more important than specific traits in determining whether a group of species thrives.
The implications extend beyond theory into conservation. Scientists warn that nearly one-third of cactus species are currently threatened with extinction, one of the highest rates among plant groups. Losing these species could mean losing entire evolutionary lineages and the potential for future biodiversity.
The study highlights that conservation efforts should not only focus on protecting existing species but also on preserving their ability to evolve. As climate change and environmental pressures intensify, this evolutionary potential may determine which species survive in the long term.
Ultimately, the research underscores a broader message: biodiversity is not just about the number of species present today, but also about the dynamic processes that allow life to adapt and flourish over time.