Final answer:
An entire group of mammals may lose the function of an enzyme due to environmental changes or mutations that make the enzyme redundant. Over generations, natural selection can lead to the widespread loss of this enzyme if it is no longer beneficial for survival. This process can be accelerated by mass extinctions that create new ecological niches and evolutionary pressures.
Step-by-step explanation:
An entire group of mammals could evolve to lose the function of an enzyme due to changes in their environment that render the enzyme unnecessary. For instance, the enzyme might be involved in processing a specific nutrient or chemical that is no longer present in the mammal's diet or surroundings. Additionally, if a mutation occurs that causes the loss of function of this enzyme but does not affect the mammal's survival, natural selection may allow this trait to spread through the population. Over time, as conditions change and certain enzymes are no longer necessary, animals with mutated genes may have an advantage as they could potentially expend less energy on producing unnecessary enzymes. If these conditions persist over many generations, the population can evolve to lose the ability to produce that enzyme entirely.
Moreover, during periods following mass extinctions, when new ecological niches become available, organisms that have lost certain enzymes may find new opportunities to thrive without them. This is because the dynamics of food sources and predators change, creating new evolutionary pressures that can lead to significant genetic shifts in surviving species.
Another factor contributing to the loss of enzyme function is the specialization of cells and organs in multicellular animals, which can contribute to certain enzymes being redundant or unnecessary in some tissues, leading to a loss of those functions in those specific cells or organs.