Mollusk Trait Evolution Slows, Becomes More Predictable

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Paleobiologist Geerat Vermeij and his research colleague Tracy Thomson have found that the evolution of mollusks has become increasingly predictable over its 540-million-year history. Their study cataloged the features of various mollusks in the fossil record and found that the frequency of new unique physical traits declined from once every 2 million years to about once every 9 million years. The researchers believe this trend reflects the feedback loops created between organisms and their environments, which allow evolutionary innovations to become more predictable over time.

Why it matters

Vermeij's research on mollusk evolution provides insights into the broader principles governing evolution and history. The idea that phenotypes, or observable characteristics, become more predictable as time goes on can be applied to the analysis of human inventions, social structures, and scientific discoveries, suggesting that early stages of any new phenomenon tend to be more unique, while later stages become more repetitive and predictable.

The details

Vermeij and Thomson identified 96 unique physical traits found in mollusks over the course of their evolution, including the spiral coiling of shells, the radula (tiny teeth-like structures used for eating), and the ventral foot (the muscular sole used for movement). Of these 96 traits, 46 (or 48%) originated during the first 96 million years of mollusk evolution, while the remaining 50 (or 52%) evolved in the succeeding 444 million years. The researchers noted that secondary peaks in the frequency of new trait development occurred following mass extinction events, suggesting that environmental constraints following such events could lead to conditions favorable for the evolution of norm-breaking physical traits.

• The study covers the 540-million-year history of mollusk evolution.
• The frequency of new unique physical traits declined from once every 2 million years to about once every 9 million years, starting around 444 million years ago.
• 46 of the 96 unique physical traits (48%) originated during the first 96 million years of mollusk evolution.
• The remaining 50 traits (52%) evolved in the succeeding 444 million years.

What they’re saying

What’s next

The researchers plan to continue studying the patterns and principles of mollusk evolution, with the goal of applying these insights to a broader understanding of the evolution of life on Earth.