Snail Evolution

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Snails belong to the class Gastropoda (“stomach-foot”), which is the largest class of molluscs and live either in water or on land (Stegenga, 2017). Snails vary widely in phenotype and can be either aquatic or terrestrial, carnivorous or herbivorous, blind or seeing, large or small, mobile or more sedentary, etc. That being said, multiple examples of evolution can be observed in these gastropods through the pre-existing variation in the species. For example, while there were originally only sea snails, there are now both sea and land snails, which are “the product of more than 3 billion years of evolutionary change” (Stanisic, 2014). For, the first land snails were seen roughly 150 million years ago, and “this group diversified, as result of …show more content…
If the snail population is exposed to the dark substrate for a prolonged period of time, then the snails’ eyes will need to adapt see better, since snails primarily move and scavenge along the ground. Therefore, the new, shadowy substrate will act as a selective force by “weeding out” snails with genes for worse eyesight than those with genes for stronger eyesight, since those with poorer eyesight will have a harder time finding food in the dark substrate. On the other hand, snails with stronger eyesight will continue to successfully find food. For example, suppose there is a population of carnivorous snails with pinhole camera eyesight. Snails with pinhole camera eyes already have limited vision, for “because there is only a small amount of light falling through the pinhole, the image will be quite dark” (Nordsieck). Therefore, in a dark substrate, it will be even more difficult for these snails to see. However, just as some humans possess stronger eyesight than others, there is also a variation in eyesight strength between snails. Accordingly, since variability is directly related to sexual reproduction (Stegenga, 2017), as fewer poor-sighted snails survive, there will be an increase in breeding between strong-sighted snails, which have been naturally “selected” to better survive in the new environment as a result of their genes,
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