Boris Johnson has claimed that a scientist who called for single-sex laboratories because "girls" are more likely to cry, was merely "pointing out a natural phenomenon".
Nobel laureate Tim Hunt caused international outrage after saying that the "trouble with girls" is that "three things happen when they are in the lab: you fall in love with them, they fall in love with you, and when you criticise them they cry."
Writing in the Daily Telegraph, Johnson claimed that Hunt's views were merely scientific observations.
"Is there any foundation to this casual assertion that women cry more readily than men?
"Well, yes, there is."
The London mayor claimed that women were more prone to "weeping" because of biological differences.
"Men are said to have differently shaped tear ducts, for instance, and can therefore retain the tears for longer before they splash down the cheek," he wrote, adding that: "Women are said to have more prolactin, a hormone associated with weeping."
He went on to compare the controversy over Hunt's comments to the recent outrage in Malaysia over "a young British woman who loosened her girdle and shook her naked breasts at the mountain."
It should not be an offence to point out gender differences, he added.
"Whether you say it is a function of biology or social expectation, it is a fact that – on the whole – men and women express emotion differently. There is, in other words, a gender difference, and it should not be an offence to say that."
This is not the first time Johnson has commented on the "emotional" difference between men and women.
In 2013, Boris suggested that many women only attend university in order to find a husband.
Responding to a comment from Malaysian prime minister Najib Razak, about the rising number of women attending university, Johnson told an audience at City Hall that "they've got to find men to marry."