Prezygotic isolating mechanisms are typically more common than postzygotic mechanisms. One explanation is that prezygotic mechanisms are less costly in terms of
and
, and so natural selection has favored them.

Question

Prezygotic isolating mechanisms are typically more common than postzygotic mechanisms. One explanation is that prezygotic mechanisms are less costly in terms of 
 and 
, and so natural selection has favored them.

BlackTom AI · Accepted Answer

This question asks for two terms to fill the blanks in the statement about prezygotic versus postzygotic isolating mechanisms.
First, consider what it means for a mechanism to be costly to an organism. In evolutionary terms, a trait or process that consumes substantial energy or depletes resources will be selected against if it does not provide proportional reproductive benefit.
For blank 1, the term that fits the idea of energetic cost is energy. Prezygotic barriers such as mate searching, courtship displays, pheromone production, and sensory processing require metabolic resources and energy expenditure. If these barriers are relatively inexpensive to produce or maintain, natural selection can favor them more readily.
For blank 2, the term that fits the idea of resource consumption beyond energy alone is resources. Many prezygotic mechanisms rely on access to or allocation of resources like time, nutrients, or territory during mate attraction and competition. If these costs are lower than the costs associated with producing and maintaining viable offspring from hybrids (postzygotic costs), selection would favor prezygotic isolation.
Now, evaluating alternative interpretations: If one suggested only energy but not resources, the statement would be incomplete because energy is a subset of the broader resource cost; conversely, naming only resources would miss the explicit energy cost portion that people often refer to in cost analyses. Since the commonly cited rationale emphasizes both metabolic energy (fuel for behaviors) and broader resource allocation (time, materials, ecological opportunities), pairing energy with resources appropriately reflects that both cost domains are relevant in explaining why prezygotic barriers can be favored.
In sum, the blanks align with the idea that prezygotic isolation is relatively cheap in terms of energy expenditure and resource use, which makes these barriers more likely to be favored by natural selection if they effectively prevent costly hybridization.

Prezygotic isolating mechanisms are typically more common than postzygotic mechanisms. One explanation is that prezygotic mechanisms are less costly in terms of and , and so natural selection has favored them.

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