Willies. They're funny looking bits of kit aren't they? And while we can all get a good laugh out of their many euphemisms – Bat & Balls, Rumpleforeskin, Just-in Beaver – we wouldn't be here without them.

But how much do you really know about penises? Given they've been swinging around for years, you might be surprised by just how many facts you never knew.

Let's start with where they came from. The world's most ancient penis dates back almost 440 million years. A five millimetre long crustacean found in Hertfordshire in 2003 became the oldest known penis on record when scientists discovered it was surprisingly similar to modern relatives. Named "Colymbosathon ecplecticos (a.k.a "astounding swimmer with a large penis” in ancient Greek) it was described as having a “copulatory organ [that] is large and stout”.

As for erections, it seems boys were born ready since doctors have been able to pick up teensy foetal erections on ultrasounds of babies still in the womb.

And for blokes worried about the size of their member, they might be pleased to hear that their pecker is longer than they thought, since half the length of their penis is inside their body.

We've compiled 39 fascinating facts to help unmask the mystery of men's manhoods. Prepare to have your mind blown...

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