Prologue
In the title for this post, I am using anatomical speech. Breasts come in pairs, of course, so talking of the breast may seem odd. But as with every paired organ in the body, anatomical speech uses the singular. I don’t know why. Talking of ‘each breast’ instead of ‘the breast’ makes sense. In each of the paired organs, the same processes take place irrespective of whether they happen to be on the left or right. And referring to ‘each breast’ also uses the same number of syllables as ‘the breast.’
What I really wanted to focus on was asking to which of the body systems (or physiological systems) does the/each breast belong. As an old professor of mine once put it—quite accurately—the mammary glands (which, with their associated fat, form the basis for the roundness of breasts) are merely modified sweat glands. That makes the milk mammals produce a form of sweat—albeit in a highly modified and nutritious form. (A comparison is worth making with the duck-billed platypus, where the infant licks milky secretions from an area of its mother’s skin rather than from teats or nipples.) Thus, breasts seem to belong quite reasonably to the integumentary system. That, after all, is the system that concentrates on the layers of the skin and associated structures: hair, nails, and the oil and sweat glands.
However, breasts also play a role in reproduction. Without their secretions, offspring would not be able to survive long after birth. Although humans have access to alternatives to breast milk, other mammals do not. So functioning mammary tissue is essential for the survival of offspring. Indeed, can we really call it reproduction or consider reproduction to have properly taken place without some way of ensuring the viability of the offspring? Especially in altricial species such as our own.
Human breasts are also described as secondary sexual characteristics. They develop during puberty in readiness for the reproductive phase in the human life cycle. In so doing, they are also signals of sexual maturity. In this respect, they are also involved in sexual attraction. Thus, they are more than just modified sweat glands.
To return to my original question, does the breast belong to the integumentary system or the reproductive system? Or does the breast overlap with both systems? Or is it an organ not fitting into the current way of defining physiological systems? If this is the case, does this ask questions of the way in which the physiological systems are currently classified? If so, we must consider other ways in which we might conceptualize the human body as a material entity.
