What does this refer to?

Hi~ In the following sentences, what does the part in blue refer to?

Social groups OR an assortment of stereotypical beliefs and attitudes?

I need to figure it out but can't. Would you take a look and comment some?

Thank you~

Recent sophisticated assessment methods have established that
people unwittingly hold an astounding assortment of stereotypical beliefs
and attitudes about social groups: black and white, female and male,
elderly and young, gay and straight, fat and thin. Although these implicit
biases inhabit us, they can constantly vary depending on our own group
membership and our everyday environments.