Question

Although primates have trichromatic vision (three types of cones), all other placental mammals are only dichromatic (two types of cones). Somewhat surprisingly, the ancestral condition for tetrapods is actually trichromatic or even tetrachromatic (four types of cones!). Based on this evidence, trichromatic vision in primates is likely a(n):

1) evolutionary reversal
2) evidence of horizontal gene transfer
3) evidence of vertical gene transfer
4) exaptation
5) polymorphy

Answer 1

Primates have trichromatic vision, meaning they have three types of cones in their eyes that allow them to see a full range of colors. This is an adaptation that may have originally evolved for other functions, but has since been co-opted for color vision.

Step-by-step explanation:

Primates have trichromatic vision, which means they have three types of cones in their eyes that allow them to see a full range of colors. This is in contrast to most other placental mammals, which are dichromatic and have only two types of cones. However, the ancestral condition for tetrapods (four-legged animals) is actually trichromatic or even tetrachromatic, meaning they have four types of cones.

Thus, trichromatic vision in primates is not an evolutionary reversal or evidence of horizontal gene transfer, but rather an exaptation. An exaptation is a trait that evolved for one purpose but has been co-opted for a different function. In this case, the trichromatic vision of primates may have originally evolved for other reasons, such as judging distances in trees, but has since been adapted for color vision.