Certain species of blind fish living in perpetual darkness in the ocean depths have evolved from ancestors that could see. Research indicates that the brain centers for vision in these fish is degenerating, whereas the brain centers controlling other senses are enlarging. What might be the MOST probable reason for the loss of vision in these fish?
A.
exposure to mutagens that caused the loss of vision
B.
progressive selection of genetic variants in the population leading to blindness as an evolutionary adaptation
C.
infection by cave-dwelling microorganisms that has led to degeneration of the eyes
D.
extreme high pressure at the ocean depths causing a deterioration of vision
I think it's B
I am inclined to agree with you.
To determine the most probable reason for the loss of vision in these blind fish, let's break down the options and analyze each one:
A. Exposure to mutagens that caused the loss of vision: This option suggests that the fish's vision degenerated due to exposure to mutagens, which are substances that can induce genetic mutations. While mutagens can indeed cause genetic changes, the fact that the brain centers controlling other senses are enlarging suggests a more specific reason for the vision loss rather than a general mutational effect.
B. Progressive selection of genetic variants in the population leading to blindness as an evolutionary adaptation: This option suggests that the loss of vision is a result of evolutionary adaptation. Over time, genetic variants that favor blindness in these fish would have been selected for, providing a survival advantage in the perpetual darkness of the ocean depths. This explanation aligns with the observed phenomenon of the brain centers for vision degenerating while those for other senses enlarge. Therefore, it is a plausible and likely explanation.
C. Infection by cave-dwelling microorganisms that has led to degeneration of the eyes: This option proposes that the loss of vision is a result of infection by microorganisms found within cave environments. While infections can certainly cause damage to bodily systems, considering that the fish are living in perpetual darkness, the chances of being infected by cave-dwelling microorganisms seem unlikely. Furthermore, the brain centers for vision specifically are mentioned to be degenerating, rather than the entire eye structure, making this option less probable.
D. Extreme high pressure at the ocean depths causing a deterioration of vision: This option suggests that the high pressure in the ocean depths is the reason for the loss of vision. However, if pressure were the main cause, we would expect to see a deterioration of the entire eye structure instead of specifically the brain centers for vision. Therefore, this option is less likely.
Considering the evidence provided in the question, the most probable reason for the loss of vision in these blind fish is B. Progressive selection of genetic variants in the population leading to blindness as an evolutionary adaptation.