Question

a scientist is studying the structural adaptations that occurred in a particular horse species over time. for several generations, the horses tended to have smaller teeth and longer toes. then, there was a shift in the fossil record, and the horses tended to have larger teeth and shorter toes. what is the most likely cause for this shift in the horses’ anatomy?

a. the environment remained stable and constant throughout the existence of the horse species.

b. the environment became overpopulated with horses of varying species.

c. the horse species traveled to a new ecosystem in a different geographical location.

d. the horses began to eat meat instead of plants.

Explanation:

To determine the cause of the anatomical shift in horses, we analyze each option:

• Option A: A stable environment would not drive significant anatomical changes over time as there would be no pressure for adaptation.
• Option B: Overpopulation with varying species would lead to competition, driving natural selection. Horses with traits (like larger teeth for different food, shorter toes for different locomotion) better suited to the new competitive environment would survive and reproduce, causing the anatomical shift.
• Option C: Traveling to a new ecosystem might cause change, but overpopulation and competition (Option B) is a more direct driver of natural selection for anatomical adaptations.
• Option D: Horses are herbivores; a shift to eating meat is not consistent with their evolutionary history.

Answer:

B. The environment became overpopulated with horses of varying species.