Which of the answers below best describes the class of questions that Insel and Young were addressing when they studied the effect of antidiuretic hormone on monogamous voles by experimentally increasing the number of receptors in the brain?

proximate; survival-value/adaptation
ultimate; developmental/ontogenetic
ultimate; mechanistic
proximate; mechanistic

Proximate; mechanistic best describes the class of questions that Insel and Young were addressing when they studied the effect of anti-diuretic hormone on monogamous voles.

Explanation:

Genetic researchers, Insel and Young, conducted various studies to analyze the neurobiological aspects of pair bonding on monogamous voles. This was done by studying the changes observed due to the action of the antidiuretic hormone, vasopressin, when their receptors were increased. The transgenic voles exhibited differential gene expressions which explained the proximate and mechanistic mating behavior.

The role of the antidiuretic hormone explained the neurochemical mechanisms of the voles mating behaviors like bonding, attachment etc. Rather than increasing the amount of hormone, just by increasing the receptors of the hormone, male voles showed an increased social reproductive behavior.