Why aren't descriptive inestigatins repeatable?

Descriptive investigations are not repeatable because they are based only on observations made at a single point in time. The results may vary at a different time. In addition, descriptive investigations do not contain variables that may indicate cause-and-effect relationships.

Explanation:

Sample response from Edg.

the darker peppered moth species were favored due to the fact that the industrial revolution had made all the nearby trees a darker color instead of white.