1 Corinthians Chapter 11 contains a list of instructions regarding how men and women should present themselves in regards to head coverings and hair length.1 Corinthians 11:14-15 says
14 Doth not even nature itself teach you, that, if a man have long hair, it is a shame unto him?
15 But if a woman have long hair, it is a glory to her: for her hair is given her for a covering.
Some more conservative Christians interpret this as applying to all Christian men, while most Christians view it as being wrong in the culture of that particular place and time. None propose an answer to the question of how exactly nature teaches us that it is a shame for men to have long hair. For instance, male lions have long manes while lionesses do not.