It's a genetic deformity.

God in his infinite wisdom causes it, of course.

Miss Margo, you are blocked.

On the one hand, mutations that arose during human evolution that conferred increased intelligence (through whatever mechanism) will have been positively selected for and fixed in the population.
Mutations that lower intelligence could be quite non-specific, diverse and far more idiosyncratic.
The idea is that, while we all carry hundreds of deleterious mutations, some of us carry more than others, or ones with more severe effects.
This means that the mutations affecting intelligence in one person may be totally different from those affecting it in another – there will be no genes “for intelligence”.
We may all carry many mutations that affect intelligence, negatively and mostly non-specifically, with the total burden determining how far away we each are from our archetypal Homo platonis.
My password is password

A receding chin is also known as retrogenia or a weak chin.
Instead of jutting out or lying flat, a receding chin slopes back toward the neck. It happens when the lower jaw – or mandible – is out of alignment with the upper jaw. It's most often a cosmetic issue,
but it can be related to more serious health concerns.

The Ugly Truth:
How Our Brains Are Hardwired Against Ugly People.
Adages like ‘beauty is only skin deep’ and ‘don’t judge a book by its cover’ have also evolved over generations to highlight the need to look beyond appearance.
But our research – a series of five studies published in Social Psychological and Personality Science – has uncovered a hard truth.
We found that our psychological bias against people and things we consider ugly is tied up in a built-in human response that’s designed to alert us to objects that may contain potentially harmful diseases.
Our work aimed to find out if this judgement was linked to our behavioural immune system; this is a set of coordinated defences evolved to protect us from diseases that uses the emotion ‘disgust’ to help us avoid a potential threat.