Salivating at the sight of food is an example of response that is evolutionarily adaptive. however, evolution can also influence the acquisition of response. it is adaptive for animals to learn to avoid eating things that and monkeys can more easily be conditioned to fear than to fear presumably because the monkeys have, for evolutionary reasons, a natural disposition to fear the former but not the latte.

Salivating at the sight of food is an example of unconditioned response.

Evolution can also influence the acquisition of conditioned/learned response.

Animals learn to avoid eating things that are harmful or cause illness.

Monkeys can more easily be conditioned to fear snakes than to fear koalas.

Explanation:

Initially, an unconditioned stimulus does not provoke any response, but after enough exposition to conditioned and unconditioned stimuli together, the simple presence of unconditioned stimuli induces conditioned responses. In this aspect, the subject has learned to predict or to anticipate the unconditioned stimulus.

Animals also learn to avoid tastes that might cause them illness or might be harmful to them, and so they also learn to ignore visual or auditory sings that help them predict illness.  

The detection of a harmful stimulus is an evolved predisposition rather than learned. Monkeys can show a detection advantage for a harmful animal such as the snake among non-harmful animals such as koalas. Indeed, snakes are an evolutionary threat stimuli in primates because most of them are poisonous.

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