the principle of comparative advantage says it's better for a country to specialize in the products it's best at producing.

This is not quite right, just as saying "evolution changes organisms so that they act to preserve the species" is not quite right.

The reason it is called comparative advantage rather than absolute advantage is that a country could be better at everything and benefit from trade. The classic example is a high powered executive who is better at typing than his* secretary. It may still be better for him to to employ a secretary than to do his own typing. He could lose more by spending time typing letters - time that could be better spent making lucrative deals - than the cost of the secretary.

*An old example, reproduced in original form.