Some of the following passages contain explanations, some contain arguments, and some may be interpreted as either an argumaent or an explanation. What is your judgment about the chief function of each passage? What would have to be the case for the passage in question to be an argument? To be an explanation? Where you find an argument, identify its premises and conclusion. Where you find an explanation, indicate what is being explained and what the explanation is.

Humans have varying skin colors as a consequence of the distance our ancestors lived from the Equator. It’s all about sun. Skin color is what regulates our body’s reaction to the sun and its rays. Dark skin evolved to protect the body from excessive sun rays. Light skin evolved when people migrated away from the Equator and needed to make vitamin D in their skin. To do that they had to lose pigment. Repeatedly over history, many people moved dark to light and light to dark. That shows that color is not a permanent trait.
—Nina Jablonski, “The Story of Skin,” The New York Times, 9 January 2007d