Question

A scientist is studying the fossil record to construct an evolutionary lineage for an order of fishes. The scientist proposes that the lineage involves long periods of little change to species and then brief periods of significant changes. Is the scientist’s proposal consistent with modern evolutionary theory?
A) Yes, the scientist is describing a pattern of punctuated equilibrium
B) Yes, but only if the brief periods of significant changes occurred after mass extinctions.
C) No, species evolve only gradually and at a relatively constant rate of change.
D) No, species evolve only gradually, although the rate of change may vary among evolutionary lineages.

Answer 1

Correct Answer: A. Punctuated equilibrium is an evolutionary theory that suggests that species remain stable/somewhat unchanging throughout most of their existence and go through rapid changes in relatively short periods. This rapid change in the species' traits is typically attributed to geologic events (ex: mountain range forming and separating 2 populations of the same species, which would lead to different selective pressures on either side of the mountain and changes in the traits of the two populations).

Incorrect Answers:

B. Mass extinctions might be a good explanation for significant changes in a species in a brief period of time (if the species was one of the species to survive the extinction), but this is definitely not the ONLY explanation for such changes in a population.

C. There are theories that suggest a gradual and relatively constant change in species throughout their existence, but there is more evidence (especially in the fossil record) and support for punctuated equilibrium.

D. ***same explanation as C***