convergent evolution occurs when species that were distinct evolve similar traits.
occurs when species that were distinct evolve similar traits?
convergent evolution
although there are no known humanoid species outside the genus "homo", the theory of convergent evolution speculates that different species may evolve similar traits, and in the case of a humanoid these traits may include intelligence and bipedalism and other humanoid skeletal changes, as a result of similar evolutionary pressures. american psychologist and dinosaur intelligence theorist harry jerison suggested the possibility of sapient dinosaurs. in a 1978 presentation at the american psychological association, he speculated that dromiceiomimus could have evolved into a highly intelligent species like human beings. in his book, "wonderful life", stephen jay gould argues that if the tape of life were re-wound and played back, life would have taken a very different course. simon conway morris counters this argument, arguing that convergence is a dominant force in evolution and that since the same environmental and physical constraints act on all life, there is an "optimum" body plan that life will inevitably evolve toward, with evolution bound to stumble upon intelligence, a trait of primates, crows, and dolphins, at some point.
humanoid
competition can cause species to evolve differences in traits. this occurs because the individuals of a species with traits similar to competing species always experience strong interspecific competition. these individuals have less reproduction and survival than individuals with traits that differ from their competitors. consequently, they will not contribute many offspring to future generations. for example, darwin's finches can be found alone or together on the galapagos islands. both species' populations actually have more individuals with intermediate-sized beaks when they live on islands without the other species present. however, when both species are present on the same island, competition is intense between individuals that have intermediate-sized beaks of both species because they all require intermediate sized seeds. consequently, individuals with small and large beaks have greater survival and reproduction on these islands than individuals with intermediate-sized beaks. different finch species can coexist if they have traits—for instance, beak size—that allow them to specialize on particular resources. when "geospiza fortis" and "geospiza fuliginosa" are present on the same island, "g. fuliginosa" tends to evolve a small beak and "g. fortis" a large beak. the observation that competing species' traits are more different when they live in the same area than when competing species live in different areas is called character displacement. for the two finch species, beak size was displaced: beaks became smaller in one species and larger in the other species. studies of character displacement are important because they provide evidence that competition is important in determining ecological and evolutionary patterns in nature.
competition (biology)