Double eyelids are hereditary. This is a biological genetic reason: double eyelids are dominant genes and single eyelids are invisible genes. If the mother in a family has a single eyelid, then she is the aa gene, and the father may be the aa or Aa gene, but if both their children have single eyelids, it means that the father must be Aa, because the mother can only provide the small A gene, while the child has a single eyelid, which is the AA gene. That means your father must have provided you with the small A gene, and he has double eyelids himself, so he has the big A gene. So he is a dominant gene and has an invisible gene, which is Aa. As mentioned earlier, the big A is dominant and the small A is invisible, so when the big A and A are combined, they show the characteristics of the dominant gene. With the invisible gene small A, they show double eyelids. In other words, all parents have double eyelids. The child must have a single eyelid. Eyes are the first of the five senses and the main visual function. Vision plays an extremely important role in people's understanding of the objective world. Usually 90% of the information obtained from the outside world is done by the eyes. It is also the expression organ and display of human inner world, which can fully reflect people's inner activities such as joy, anger, yearning and joy, so it is called the window of the soul. It is the most enlightening and striking organ in human appearance and the center of beauty.