Question

question 1-15
a newborn of a mammal has a wide range of birth weights. individuals with very low birth weights often do not survive, and individuals with very high birth weights lead to complications during birth. over generations, most individuals are born with medium birth weights and survive to become adult organisms.
based on this information, which statement best explains how stabilizing selection affects the likelihood of speciation in this population?

• stabilizing selection favors new mutations that lead directly to the formation of new species.
• stabilizing selection favors extreme traits, causing rapid divergence into two or more species.
• stabilizing selection decreases variation, making speciation less likely because most individuals remain genetically similar.
• stabilizing selection causes reproductive isolation between groups with different traits, increasing the rate of speciation.

Explanation:

The question is about stabilizing selection and its effect on speciation. Stabilizing selection favors intermediate traits (like medium birth weights here), reducing variation. Less variation means individuals are more genetically similar, so speciation (formation of new species) is less likely as speciation needs genetic divergence. Let's analyze options:

• Option 1: Stabilizing selection doesn't favor new mutations for new species; it favors intermediates. Eliminate.
• Option 2: Stabilizing selection reduces variation, not cause rapid divergence (that's disruptive selection). Eliminate.
• Option 3: Stabilizing selection decreases variation (favors intermediates, so extremes are selected against), making individuals genetically similar. This reduces the likelihood of speciation as speciation requires divergence. This matches.
• Option 4: Stabilizing selection reduces variation, so it would decrease, not increase, speciation rate. Eliminate.

Answer:

The correct option is the third one (the option stating "Stabilizing selection decreases variation, making speciation less likely because most individuals remain genetically similar"). (Assuming the options are ordered as: 1. Stabilizing selection favors new mutations...; 2. Stabilizing selection causes rapid divergence...; 3. Stabilizing selection decreases variation...; 4. Stabilizing selection causes... increasing speciation rate. So the answer is the third option's text as per above analysis.)