They are close friends in the beginning of the play. http://webcache.googleusercontent.com/search?q=cache:yDbvfIrZYaAJ:www.studynotes.ie/wiki/macbeth-ban...
Biology does influence gender development. For example, some differences between typical boys and girls can be explained by the effect of genes on sex chromosomes, and by the levels of sex hormones and their effect on the brain during early development (e.g., prenatal exposure to high levels of male-typical hormones).
