Complexity of Evolution

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Hoping for a simple, straightforward explanation, Leonardo Vintini (“The Night of the Trilobites, Parts I and II” Aug. 10 and Aug. 17) makes the mistake of assuming that if a trait (left-curling in snails) protects them from a major predator then natural selection would predominantly favor that trait. Inheritance seldom works that cleanly. For example, some moths when detecting the echolocation of bats become immediately immobile, some even feign death.

If this is such a fabulous tactic, why don’t all moths select for those features? It is because other factors are at play. Left-curling may make the snail more vulnerable to other conditions. Right-curling may confer strengths the left-curlers don’t have. More likely the gene selection transmitted by the mothers and by the fathers may be subject to various imprinting effects that have other limitations besides yielding a crab delicacy.

Genetic expression requires not just the presence of certain genes, but the absence of imprinting silencers on one or the other parent’s contribution, each of which includes patterns not immediately evident. As in most cases, more than one explanation is necessary to cover the options. In this case, both small changes and large population shifts due to “extreme environmental change” are both applicable. Evolution marches on.

Larry Hourany, Ph.D.
McKinleyville, California