1) There are 2 types of worms: worms that eat at night (nocturnal) and worms that eat during the day (diurnal). The birds eat during the day and seem to be eating ONLY the diurnal worms. The nocturnal worms are in their burrows during this time. Each spring when the worms reproduce, they have about 500 babies but only 100 of these 500 ever become old enough to reproduce.

a. What worm has natural selection selected AGAINST? _ FOR? _

Natural selection is an evolutive force, that selects genotypes expressing a higher fitness or aptitude. Natural selection acts against the diurnal worm and favoring the nocturnal one.

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Natural selection, as an evolutive force, selects beneficial alleles and increases their frequency in the population.

It is the result of the phenotype-environment interaction which determines gene destiny in space and time.

It is the differential capability of individuals to leave offspring.

Natural selection results in adaptation, which means the increase of the aptitude phenotype.

Aptitude (or fitness) is reflected by the phenotype that results in the survival, fertility, and capability of having a mate.

Natural selection can act favoring an allele or against it, according to how it affects the fitness of individuals.

In many cases adaptations, resulting from natural selection can be correlated to environmental factors or selective pressures applied by other organisms or habitats.

The selective agent is the environmental trait that determines the differential survival of the phenotypic classes.

The environment influences the probability that each genotype passes its gametes to the next generation.

Knowing this, we can analyze the xposed example.

We can think about birds as the selective modeling pressure ⇒ environmental pressure.

There are two phenotypes

diurnal worms
nocturnal worms

Fact ⇒ Birds only prey on diurnal worms.

This is significant pressure because birds might prey on the few worms that make it to the reproductive stage. And if so, their reproductive capability reduces significantly.

On the other hand, the nocturnal worms do not face this predator. Hence, their chances to get to the reproductive stage, reproduce, and leave fertile offspring, are higher than the ones of the diurnal worm.

Conclusion:

So, as birds reduce the chances of diurnal worms to reproduce, the nocturnal worm leaves fertile offspring and increases the population size.

Natural selection in this example is acting against the diurnal worm and favoring the nocturnal one.

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