Like you didn’t already suspect this:
In an Anglo-Saxon book of poetry kept at Exeter Cathedral, researchers from Britain’s Wolverhampton University have unearthed a joke that suggests the clichéd ribaldry of a millennium ago is awfully similar to what passes for humor today. The translation, as cited by the Telegraph, reads: “What hangs at a man’s thigh and wants to poke the hole that it’s often poked before? Answer: A key.”
Hur hur hur hur! (wheeze)
And they have found evidence of Egyptians laughing at similar versions of wit. Researchers at Wolverhampton say the jokes they have found in delicate manuscripts and carved on stone tablets thousands of years old demonstrate a common idea of what’s funny across the ages of humanity: flatulence, sex and “stupid people,” as one academic tells the Telegraph.
So when the Doctor tells you that the only thing he can depend on on Earth is human nature… better believe him. 
