The aphid is a species of insect that feeds on plants and is a member of the superfamily Aphidoidea. There are some 4,000 known species of aphids, divided into 10 families. The oldest aphids so far identified lived in the Carboniferous period (354 to 290 million years ago). They have not changed in the least in the more than 300 million years since. The 50-million-year-old aphid preserved in amber in the picture is evidence that these insects have not changed since the day they first came into being, in other words, they have not evolved.