Question

2. Imagine a population of crabs living on a white sandy beach. The crabs ONLY occur in two colors- red and blue, each controlled by color genes. Over time, will the crab population shift toward white? Why or why not?

Answer 1

Natural selection benefits individuals with better fitness, increasing their frequency in populations. In the exposed example, white individuals can camouflage better from predators and get to survive and reproduce.

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Natural selection is the result of the phenotype-environment interaction which determines gene destiny in space and time, selecting beneficial alleles and increasing their frequency in the population.

Natural selection results in adaptation, which means the increase of the aptitude phenotype. Aptitude is the contribution of each genotype to the next generation.

Aptitude (or fitness) is the phenotype that results in the survival, fertility, and capability of having a mate. It is a way of measuring the individual ability to leave fertile offspring. Aptitude must be significant to the natural selection act in its favor.

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

In the exposed example, color differences between the substrate and the crabs' bodies make them more vulnerable to the attack of predators. If this is the case, predators are acting as selective pressure or modeling environmental factor.

Red and blue crabs probable are easily seen against a white sand substrate. So the crabs' population exhibiting these colors suffer from high predation pressure.

Individuals expressing white color can camouflage better and are not seen by predators. Hence, they get to survive more in comparison with colored individuals. So crabs' response to the selective pressure is survival of white or clear individuals.

Natural selection benefits white individuals, who manage to survive and reproduce, expressing a higher fitness. The white color trait begins to spread into the whole population, and finally, it shifts towards white.

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