Adaptive Value:

Adaptive Value

There is believed to be little adaptive value associated with conditioned taste aversion in parasitic animals that feed on the blood of vertebrates, and therefore it is thought that the systems associated with this behavior have deteriorated over time through a lack of stabilizing selection.  Two reasons proposed for this absence of adaptive value are: 

1) Blood is not a good medium for carrying toxins in the live host since the host must be able to survive the circulating blood.  It is therefore unlikely that a high concentration of toxins would develop.

2) Sanguinivorous bats may have had to overcome nauseating effects of blood ingestion early in their evolution.   Ratcliffe et. al. states that "Microchiropteran bats, like humans, have simple stomachs.  For humans, symptoms of blood ingestion....include nausea, vomiting and diarrhoea."  If bats have a reaction similar to humans, early sanguinivores would need the ability to ignore the nausea caused by the food source and continue to ingest that food. 

desmodus rotundus @

Vampire bat.

Photo found at