Which snail population has the larger average shell thickness, the population from 1871, or the population from the 1980s?

the population from the 1980s had larger average shell thickness.

Explanation:

The snail population from the 1980s had larger average shell thickness.

The reason is explained as follows.

In the 19 the century , a species of crab called green crab moved to North America . They moved to Cape Cod region . They were predators and used to feed on snails . So a new species of snail evolved there which had thicker cover of shell to protect them from their predators. This was a burning example of process of evolution in modern times. The present generation of snails there now had thicker shell than their ancestors.