A Twitter user posted this tweet on Twitter.com earlier today:

Knowing that EVERY penis started out as a vagina should help u to better understand why some men are such bitches

Twitter user @bprocks56, a male, asked: “how is that when Adam was created before Eve? #blankstare”

I saw this as a teachable moment: clearly some people aren’t aware that all embryos have the same female genitalia until about the 8-12 weeks of gestation. This is why the sex of a baby can’t be determined by ultrasound until after the sex organs are formed.

Here are male and female 9 week old embryos. Can you tell which is which? Click here to see the answer.

Image source: DM