Final answer:
An evolutionary constraint is a limitation on the ability of a species to evolve certain traits. Examples include the inability of land-dwelling mammals to evolve gills and the limited availability of certain habitats.
Step-by-step explanation:
An evolutionary constraint refers to a limitation or restriction on the ability of a species to evolve certain traits or adaptations. These constraints occur due to various factors such as genetic or physiological limitations, ecological contexts, or historical constraints.
Two examples of evolutionary constraints include the inability of land-dwelling mammals to evolve gills for underwater respiration due to their physiological limitations, and the limited availability of certain habitats restricting the evolution of certain traits in species that are highly specialized to their current environment.
The occurrence of evolutionary constraints highlights the fact that not all traits are adaptive. Some traits may be limited or prevented from evolving due to physical or environmental constraints, even if they could be beneficial for the survival and reproduction of individuals.