[AndrewC]

Humans are apes. QED.

I don't think so.

ape    ( P )  Pronunciation Key  (p)
n.

1. 1. Any of various large, tailless Old World primates of the family Pongidae, including the chimpanzee, gorilla, gibbon, and orangutan.
   2. A monkey.
2. A mimic or imitator.
3. Informal. A clumsy or boorish person.

http://www.britannica.com/eb/article-67269 ----(human evolution)

Hominidae are distinguished from Pongidae (anthropoid apes) by evolutionary trends that illustrate the adaptations of each for different environmental situations.

[bobdsmith]

It used to be true that apes didn't include humans but now they do.

Humans are more closely related to chimpanzees than chimpanzees are to gorillas. If chimpanzees and gorillas are apes, then so are humans. That seems to be the general reasoning behind it.

Wikipedia explains it in a lot of detail: http://en.wikipedia.org/wiki/Ape#Historical_and_modern_terminology (which is where I read it)

[WildHorseCrash]

The definition you cited is an old, old definition. (Notice, for example, the medieval manner in which Pongidae is defined.) The wikipedia article cited by another poster is pretty good in explaining the evolution of this taxonomic classification to its modern form.

And while you are right that wikipedia is not a primary source, it is equally true that neither the American Heritage Dictionary of the English Language nor the Encyclopedia Britannica is the arbiter of scientific knowledge. When defining "ape" scientifically, both of these sources are irrelevant.

This is an abstract discussing some of the modern taxonomy