Question

The concept of punctuated equilibrium suggests that a the rate of evolution is constant, with short time periods of no evolutionary change. b evolution occurs gradually over time. c small genetic changes accumulate over time to allow for phenotypic change and speciation. d long periods of little evolutionary change are interrupted by short periods of major evolutionary change. e both b and c

Short answer

The correct answer is 'd'. The concept of punctuated equilibrium suggests that long periods of little evolutionary change are interrupted by short periods of major evolutionary change.

Step-by-step solution

Background Understanding

Knowing the basics of different evolutionary theories is crucial in solving this problem. Understand that punctuated equilibrium theory is the proposition that species evolution is not uniform but happens quickly in spurts, 'punctuating' long periods of stability or equilibrium.

Check Each Option

'a' and 'b' are incorrect because they suggest uniform or constant evolution which contradicts the punctuated equilibrium theory. 'c' implies a constantly accumulating change which again contradicts the theory. 'e' combines 'b' and 'c', so it's incorrect as well.

Pick the Correct Option

'd' is the correct choice. 'Long periods of little evolutionary change are interrupted by short periods of major evolutionary change.' This statement aligns perfectly with the concept of punctuated equilibrium.

Key concepts

Evolutionary Theories

Understanding evolutionary theories is fundamental to grasping the nature of biological change over time. Evolution encompasses the process by which species adapt and diversify, and several theories aim to explain how this occurs. The most widely accepted one is Darwin's theory of evolution by natural selection, which suggests that organisms better adapted to their environment tend to survive and reproduce more than those less adapted, leading to a gradual change in the population.

However, punctuated equilibrium presents an alternative view. Coined by paleontologists Niles Eldredge and Stephen Jay Gould, this theory posits that species evolution is characterized by relative stability for most of their history, 'punctuated' by brief, drastic changes that result in new species. These abrupt shifts, which paleontological evidence supports, contrast with the gradualism of traditional Darwinian theory. By providing a larger viewpoint of how species have evolved through different mechanisms, this helps students who might struggle to reconcile the seeming sudden appearance of new species in the fossil record with gradualism.

Species Evolution

Species evolution is the process by which new biological species arise. For students looking at an evolutionary tree, it might seem that species change at constant rates. However, punctuated equilibrium challenges this notion. It suggests that the lineages remain relatively unchanged, not evolving for most of their existence. These stable periods are then followed by short, evolutionary bursts during which new species emerge rapidly in geological terms.

It's essential to understand that 'rapid' in this context still means thousands to millions of years. Punctuated equilibrium addresses the patterns we see in the fossil record, where there are long stretches with no apparent change in species, followed by sudden shifts where new species appear without obvious intermediate forms. The theory essentially states that evolution is not a steady, unbroken process but rather one that happens in fits and starts.

Phenotypic Change and Speciation

Phenotypic change refers to alterations in an organism's observable traits. Speciation, the formation of new and distinct species, often relies upon phenotypic change as these traits, which are influenced by genetic variation, can lead to reproductive isolation. In the context of punctuated equilibrium, phenotypic changes that give rise to new species occur rapidly in geological time, during those short periods of intense evolutionary change.

For example, a small population might become isolated from its parent population due to a geographical barrier. Over time, the isolated group undergoes significant phenotypic changes due to genetic drift, natural selection, or both. When these changes are sufficient to prevent the isolated group from interbreeding with the original population if they were to come into contact again, speciation has occurred. The idea that these changes happen rapidly, followed by long periods of little or no change, is central to the concept of punctuated equilibrium and helps students understand why we might not see incremental steps in fossil records.