Problem 2 - Campbell Biology

Question

According to Hamilton's rule, (A) natural selection does not favor altruistic behavior that causes the death of the altruist. (B) natural selection favors altruistic acts when the resulting benefit to the recipient, corrected for relatedness, exceeds the cost to the altruist. (C) natural selection is more likely to favor altruistic behavior that benefits an offspring than altruistic behavior that benefits a sibling. (D) the effects of kin selection are larger than the effects of direct natural selection on individuals.

Step-by-Step Solution

Answer

B

Step 1: Understand Hamilton's Rule

Hamilton's rule states that an altruistic act is favored by natural selection if R × B > C, where R is the genetic relatedness between the altruist and the recipient, B is the benefit to the recipient, and C is the cost to the altruist.

Step 2: Identify Correct Answer

From the possible answers, identify which one fits Hamilton's rule. Look for the explanation that mentions a benefit to the recipient that, when adjusted for relatedness, is greater than the cost to the altruist.

Step 3: Compare Other Choices

Evaluate the other options to ensure the chosen answer is correct. Answer (B) states: natural selection favors altruistic acts when the resulting benefit to the recipient, corrected for relatedness, exceeds the cost to the altruist. This matches Hamilton's rule.

Key Concepts

Altruistic Behavior

Altruistic behavior is when an individual acts in a way that benefits another at a cost to themselves. This behavior might seem counterintuitive in the context of survival and reproduction. However, from an evolutionary perspective, it can make sense due to the genetic ties between individuals. For example, when a mother bird risks her life to protect her young, she is ensuring the survival of her genes through her offspring. Altruistic behavior is key to understanding complex social structures in animals and even humans.

Natural Selection

Natural selection is a fundamental concept in biology that explains how traits that enhance survival and reproduction become more common in a population over generations. In essence, this process 'selects' for traits that improve an organism's chances of passing on its genes to the next generation. Conversely, traits that are detrimental to survival tend to be weeded out over time. Altruistic behavior might seem at odds with natural selection since it often involves a cost to the altruist. However, when the benefits to genetically related individuals are factored in, natural selection can indeed favor these behaviors.

Genetic Relatedness

Genetic relatedness is a measure of how many genes two individuals share. It is the cornerstone of Hamilton's rule, which postulates that altruistic acts can evolve if they benefit related individuals enough to outweigh their costs. For example, siblings share about 50% of their genes, so helping a sibling can indirectly help an individual pass on their genetic material. Hamilton’s rule is mathematically expressed as \[\begin{equation} \text{R} \times \text{B} > \text{C} \ \text{R} = \text{Genetic relatedness} \ \text{B} = \text{Benefit to recipient} \ \text{C} = \text{Cost to altruist} \end{equation}\]. A higher genetic relatedness can increase the likelihood of altruistic acts because the altruist is indirectly ensuring their own genetic material is preserved.