Inbred

We who from daily experience knew Miss Smedley like a book—were we not only too well aware that she had neither accomplishments nor charms—no characteristic, in fact, but an inbred viciousness of temper and disposition?

His cold experience tempers all his heat, And inbred worth doth boasting valour slight.

The Lavender Quill Society, that group of in-bred Manhattan gay writers who believe that gay literature begins and ends in their clique (outsiders need not apply for membership).

The level of academic inbreeding differs between countries and continents. Macháček et al. (2022) reported that in North America only 31% of all researchers are inbred (based on 22 major fields of science), while in Asia, this proportion is 55%, in Western and Northern Europe 37% and in Central and Eastern Europe reaches nearly 79% which is the highest proportion of inbreeders on the global scale.

Since you all marry your cousins I bet you're a bunch of inbreds.

People discovered that the Belgian hare of those days was a very delicate animal and that it was subject to many diseases. It had been inbred so long in order to produce show animals that its vitality was nearly gone.