BIT

Bitter Taste Aversion

Class: I - Natural Selection

EPA Total Score: 28 /100

Glendinning, J. I. (1994). Is the bitter rejection response always adaptive? Physiology & Behavior, 56(6), 1217-1227.

Abstract: The bitter rejection response consists of a suite of withdrawal reflexes and negative affective responses. It is generally assumed to have evolved as a way to facilitate avoidance of foods that are poisonous because they usually taste bitter to humans. Using previously published studies, the present paper examines the relationship between bitterness and toxicity in mammals, and then assesses the ecological costs and benefits of the bitter rejection response in carnivorous, omnivorous, and herbivorous (grazing and browsing) mammals. If the bitter rejection response accurately predicts the potential toxicity of foods, then one would expect the threshold for the response to be lower for highly toxic compounds than for nontoxic compounds. The data revealed no such relationship. Bitter taste thresholds varied independently of toxicity thresholds, indicating that the bitter rejection response is just as likely to be elicited by a harmless bitter food as it is by a harmful one. Thus, it is not necessarily in an animal's best interest to have an extremely high or low bitter threshold. Based on this observation, it was hypthesized that the adaptiveness of the bitter rejection response depends upon the relative occurrence of bitter and potentially toxic compounds in an animal's diet. Animals with a relatively high occurrence of bitter and potentially toxic compounds in their diet (e.g., browsing herbivores) were predicted to have evolved a high bitter taste threshold and tolerance to dietary poisons. Such an adaptation would be necessary because a browser cannot “afford” to reject all foods that are bitter and potentially toxic without unduly restricting its dietary options. At the other extreme, animals that rarely encounter bitter and potentially toxic compounds in their diet (e.g., carnivores) were predicted to have evolved a low bitter threshold. Carnivores could “afford” to utilize such a stringent rejection mechanism because foods containing bitter and potentially toxic compounds constitute a small portion of their diet. Since the low bitter threshold would reduce substantially the risk of ingesting anything poisonous, carnivores were also expected to have a relatively low tolerance to dietary poisons. This hypothesis was supported by a comparison involving 30 mammal species, in which a suggestive relationship was found between quinine hydrochloride sensitivity and trophic group, with carnivores > omnivores > grazers > browsers. Further support for the hypothesis was provided by a comparison across browsers and grazers in terms of the production of tannin-binding salivary proteins, which probably represent an adaptation for reducing the bitterness and astringency of tannins. Tannins are a widespread class of plant compound that are abundant in the diet of browsers (i.e., forbs, shrubs and trees) but rare in that of grazers (i.e., grasses). Whereas browsers produce large quantities of tannin-binding proteins, grazers produce none. Finally, it was found that species with a high bitter threshold (i.e., herbivores) were generally more tolerant to toxic compounds. This latter adaptation would minimize the risk of toxicity after unwittingly ingesting foods laced with nonbitter poisons.

DJGlass


Supporting Evidence

11/100

Submitted by DJGlass

11/100

Submitted by DJGlass

No one has (yet) rated this source as containing any supporting Medical evidence for this EPA.

No one has (yet) rated this source as containing any supporting Physiological evidence for this EPA.

No one has (yet) rated this source as containing any supporting Cross-Cultural evidence for this EPA.

No one has (yet) rated this source as containing any supporting Genetic evidence for this EPA.

11/100

Submitted by DJGlass

No one has (yet) rated this source as containing any supporting Hunter-Gatherer evidence for this EPA.

Supporting Evidence is evidence that suggests that this trait is an Evolved Psychological Adaptation (EPA) - i.e., that it has been shaped by natural selection to solve a particular adaptive problem.

Challenging Evidence

11/100

Submitted by DJGlass

11/100

Submitted by DJGlass

No one has (yet) rated this source as containing any challenging Medical evidence for this EPA.

No one has (yet) rated this source as containing any challenging Physiological evidence for this EPA.

No one has (yet) rated this source as containing any challenging Cross-Cultural evidence for this EPA.

No one has (yet) rated this source as containing any challenging Genetic evidence for this EPA.

11/100

Submitted by DJGlass

No one has (yet) rated this source as containing any challenging Hunter-Gatherer evidence for this EPA.

Challenging Evidence is evidence that suggests that this trait is not an EPA - e.g., that it is a product of cultural learning or genetic drift, or maybe it does not exist at all. However over each line of evidence for a description.