Final answer:
Carnivores may have lost sweetness receptors because they evolved to prioritize the detection of bitter tastes, indicative of toxic substances, which is crucial for their dietary needs and survival. Taste aversion research supports the idea that avoiding harmful substances contributes to species survival, while sweetness generally signals beneficial relationships with plants, which are not as relevant to carnivores.
Step-by-step explanation:
During evolution, carnivores may have lost functional sweetness receptors because their diet does not typically include foods that require them to distinguish sweet tastes. In the context of survival and dietary needs, the ability to detect bitter tastes, which could indicate the presence of toxic substances, is more critical for carnivores. This is supported by research into taste aversion, which suggests that animals have evolved to avoid harmful substances as a means of species survival via natural selection. Moreover, since bitter and sweet tastes can often be found together in the wild, the development of a strong bitter taste response was likely more beneficial for carnivores to prevent the ingestion of poisons. Plants, on the other hand, developed sweet substances to attract animals and aid in seed dispersal, a relationship not directly beneficial to carnivores.