Breast development extension adrenocorticotropic hormone (ACTH)), and thyroid hormones such as thyroxine (and by extension thyroid-stimulating hormone (TSH) and thyrotropin-releasing hormone (TRH)) also play permissive but less well-understood/poorly-characterized roles in breast development during both puberty and pregnancy, and are required for full functional development. Leptin has also been found to be an important factor in mammary gland development, and has been found to promote mammary epithelial cell proliferation. In contrast to the female-associated sex hormones, estrogen and progesterone, the male-associated sex hormones, the androgens, such as testosterone and dihydrotestosterone (DHT), powerfully suppress the action of estrogen in the breasts. At least one
Sexual conflict selection, continuous sexual conflict creates an environment in which mating frequency and male secondary sexual trait development are somewhat in step with the female's degree of resistance. It has primarily been studied in animals, though it can in principle apply to any sexually reproducing organism, such as plants and fungi. There is some evidence for sexual conflict in plants. Sexual conflict takes two major forms: Sexual conflict may lead to antagonistic co-evolution, in which one sex (usually male) evolves a favorable trait that is offset by a countering trait in the other sex. Similarly, interlocus sexual conflict can be the