Final answer:
The sheep liver fluke's complex life cycle evolved through natural selection to ensure its survival across multiple hosts. Flukes do not have sight; they rely on chemical cues, whereas a dog's color vision is limited, causing difficulties in distinguishing red birds in green grass due to red-green color blindness.
Step-by-step explanation:
The life cycle of the sheep liver fluke is complex and involves two hosts, which typically includes a snail and a sheep or other grazing mammal. This parasitic organism evolves such a complicated life cycle as a strategy to ensure survival and reproduction in diverse environments. Through natural selection, traits that favor successful transmission and infection of both intermediary and definitive hosts are favored and passed down.
Regarding vision and color perception, the life cycle of the sheep liver fluke does not involve sight as flukes do not possess eyes or visual systems. Instead, they rely on chemical cues to navigate their environment. In animals, the ability to see in color varies, with humans and other primates possessing a better sense of vision with three-dimensional and color perception abilities.
For example, a dog has difficulty identifying a red bird in green grass because they are red-green color-blind, possessing only two types of cone cells that mostly detect blue and yellow. Therefore, the red bird would appear as shades of grey to a dog and blend in with the grass, making it harder for the dog to spot it.