Here's why it happens:
* Genetic Basis: The genes responsible for mammary gland development are present in both male and female mammals.
* Hormonal Influence: While these genes are present, their expression is regulated by hormones. In females, estrogen and progesterone trigger the development of mammary glands and nipples into functional organs.
* Male Development: In males, testosterone levels are high during fetal development, which suppresses the expression of genes related to mammary gland development. However, the initial development of these structures still occurs.
Even though male cats have nipples, they are non-functional and do not produce milk.