Final answer:
Quantitative traits in populations such as weight and height typically distribute in a bell-shaped curve due to polygenic inheritance, with most individuals near the average and few at the extremes.
Step-by-step explanation:
Length, weight, and many other quantitative traits in a population tend to show variation that, when plotted on a graph, looks like a bell-shaped curve. This phenomenon is observed in traits that are governed by polygenic inheritance. This means most individuals in a population will fall within the middle range of a particular trait, such as average height or weight, with fewer individuals at the extremes.
For example, if we analyze height in human populations, we find that most people have average height, but very few are extremely tall or extremely short. A bell-shaped curve effectively represents this distribution. It is important to have a representative sample size to observe the bell curve accurately in natural populations. Without a large sample, the distribution may not accurately reflect the broader population's characteristics.