Around 7,000 years ago, conches living near Panama's Caribbean shores grew large and fat. Around 1,500 years ago, however, humans discovered that these large sea snails make for tasty eating. Those ancient humans began selecting for the bigger shells: The bigger the conch, the more meat it offered. As a result, they inadvertantly drove the evolution of the species toward a smaller shell size at maturity, Smithsonian researchers recently discovered.
The researchers arrived at this conclusion after comparing fossil conch shells and those from the archaeological record with ones from today. Around 7,000 years ago, they found, conches were about 66 percent bigger when they reached sexual maturty (indicated by lip thickness) than they are today. Around 1,500 years ago, the researchers report, the conches began experiencing a serious decline in size, most likely due to humans snatching them up.
The conch's story is a bit different than that of the many species of fish whose average size has shrunk due to intense overharvesting. There was no large-scale conch-harvesting industry whiping out massive numbers of the snails. Given this difference, the researchers think that the shrinking conches might be the first example ever discovered of an animal's evolution being driven by low-intensity human actions.
The trend toward mini-conches, however, might be reversible. As the researchers point out, conches living in protected areas seem to be shifting in the opposite direction. They grow bigger than those animals living in fishing-friendly places, and seem to be reclaiming a bit of their former, meaty glory.