Chapter 5: Laws of Variation Summary and Analysis

Variations in organisms are not the product of chance. They are caused, at least in part, by the external conditions of the organisms as well as changes to the reproductive systems of parents bearing offspring. However, it is not understood why changes to reproductive systems would produce specific changes in the offspring.

The amount of variation that can be attributed to external conditions such as climate and food is likely small. While biologists have certainly found examples of the same species having different appearances in different climates or regions—such as some birds being differently colored when near the ocean—these variations tend to be less significant than other differences between organisms. However, the fact that species do vary in this why from external factors helps demonstrate the point that the species were...