Mathematical Biology Joke

I found this rather entertaining mathematical biology joke. You can read the context at The Loom.

A shepherd is tending his sheep, and a man comes by and says, "If I guess the correct number of your sheep, can I have one?"

The shepherd says, "Please try."

The man looks at the flock and says "Eighty-three."

The shepherd is completely amazed that he got the right number. The man picks up a sheep and starts to walk away.

The shepherd says, "Wait! If I guess your profession, can I have my sheep back?"

The man says, "Sure."

The shepherd says, "You must be a mathematical biologist."

The man says, "How did you know?"

"Because you picked up my dog."