A person’s biological sex usually refers to their status as female or male depending on their chromosomes, reproductive organs, and other characteristics. Chromosomes are tightly packed DNA, or molecules that contain the genetic instructions for the development and functioning of all living things. Humans typically have forty-six chromosomes. Two of those are sex chromosomes that contain instructions for the development and functioning of characteristics related to biological sex, such as reproductive organs. There are two kinds of human sex chromosomes, X and Y. Individuals identified as males tend to have one X and one Y chromosome, while those identified as females tend to have two X chromosomes. However, other people are born with other chromosome combinations, such as XXY, that lead them to develop a mix of characteristics. People who fit that description are often referred to as intersex, a category for people whose bodies do not conform with stereotypical expectations of males or females at birth.

Taken from here

Evidence seems pretty strong to me.