Smell: The Sense Responsible for the Miracle of Life

The bond between mother and child is one that develops almost instantly after birth, basically as soon as the mother and child get in close enough contact to smell one another. That's right, smell. The sense of smell is one that goes underrated in our human society based primarily on sight and sound, but it is one that has great influence over a lot of our behaviors. That mother and child never would have had that chance to bond if it weren't for smell because the mother wouldn't have been pregnant in the first place; smell is one of the necessary senses in finding a mate. Smell plays a roll from initial attraction of possible mates, through pregnancy, up to birth and development of the baby.
Our olfactory systems can respond to chemicals that we either are aware of as odors, or the chemicals can go unnoticed by our I-functions. Those chemicals that we are aware of as scents start on receptors on the sensory cells in the nose, which pass the signal on to the olfactory bulb, located under the frontal lobe in the brain. Only then does the signal get passed on to the cortex (1). The unconscious response to certain chemicals is most likely processed through the vomeronasal organ (VNO), which is located on either side of the nasal septum. Pheromones are odorless chemicals, processed through the olfactory system, that influence sexual behavior and attractiveness (2). So these colorless, odorless molecules are released in everyone's natural body odors, hoping that the right mate will process them, fueling attraction.
A man and a woman sit next to each other on a couch at a house party. They chat, all the while unconsciously absorbing one another's pheromones. The woman spent the afternoon with her nursing sister and niece. Exposure to the compounds released by the mother and infant, caused an unconscious increase in sexual desire for the woman (3). The couple discovers a mutual attraction. One thing lead to another, some time passes, and the woman finds out that she is pregnant. This theoretical situation might not have gone anywhere had this couple not found attraction in smell. Finding attraction through someone else's pheromones is evolutionarily beneficial, because humans usually smell best and appeal most to others who have certain genetic immunities to diseases that is most different from the others' own genetic make-up (4). Therefore, this resulting pregnancy has a higher chance to have stronger genetic resistance to disease.
The theoretical woman is now in the midst of her first trimester, and is miserable. She feels sick all the time; basically any smell makes her nauseated. She is at the height of morning sickness, and her brain circuits in the olfactory system have become rewired (5). Her olfactory sensory neurons are extremely sensitive to strong odors, so she is brutally aware of the presence of any sort of pungent smell (6). Although she may feel absolutely miserable, her morning sickness is a good sign for the health of her fetus. The sensitivity to odor stems from the fact that early on in development the fetus is very sensitive to anything that the mother puts in her body, so when the mother has a strong aversion to pungent smells she is less likely to consume whatever the source of the smell is. This sort of unconscious protection actually works: nausea and vomiting during pregnancy is associated with better pregnancy outcome (7). Sensitivity to smell early on in pregnancy is actually beneficial for the fetus in the long run.
Six more months pass, and the baby is born at last. Within minutes after birth, the baby is placed on her mother. The close physical contact starts the bonding between mother and infant. The baby can smell her mother's olfactory cues emitting from her nipples, which draws her in to breastfeed. If an infant is exposed right away to his mother's breast, he will be able to recognize his mother's milk over other lactating woman, and will breastfeed for longer stretches of time (8). This initial skin-to-skin contact imprints the olfactory cues of the mother onto the infant, making him able to recognize his own mother over other mothers, and receive more nutrients through longer periods of breastfeeding. A child shows preference for his mother's smell over that of other mothers up until about age 5 (9). The infant also gets imprinted onto the mother. After only a 10-minute to 1-hour exposure to her baby, 90% of mothers can correctly identify her infant through smell alone (10). The role of smell in bonding between mother and child makes evolutionary sense. As a mother, being able to recognize your infant among other babies is important if you want to raise your child, not your neighbor's, into adulthood to successfully pass on your genes. As an infant, you want to be able to recognize the mother that is responsible for you, will take care of you, and most importantly, feed you, so you need to know what that breast smells like.
Smell plays an extremely strong evolutionary role. Unconscious olfactory mechanisms control for the attraction of genetically different mates, while more conscious mechanisms make sure a pregnant mother doesn't consume anything to harm her developing fetus. After birth, the smells exchanged between mother and infant make sure their bond remains strong, leading to longer breastfeeding times which leads to a stronger infant. Also, this makes sure a mother and infant can find each other out of the sea of mothers and infants there are. All of these traits make sure that offspring is as genetically and physically strong as possible.
In our culture where we deny natural body smell, covering it up and washing it away constantly, it turns out that we are fighting against nature. The smells and pheromones that we release and that ultimately get processed by other people's nervous systems transmit fairly complex information. Although we try our best to suppress our own natural scent, the chemicals get released anyway, communicating with those around us. The brains of our neighbors take in and process this information, all without influence from the I-function. Our brains know what's good for us even though we're not aware of it-helping us choose mates to conceive and raise successful offspring. In conclusion, the sense of smell, probably the most unappreciated sense, plays a strong hand in the perpetuation of the human race. It helps make sure offspring are viable even from before the act of conception on through early postnatal development. So appreciate the olfactory system, it helped you get here.

Sources Cited
1. The Vivid World of Odors

2. Pheromones and Mammals

3. Social chemosignals from breastfeeding women increase sexual motivation

4. Pheromones: Potential Participants in Your Sex Life

5. Louann Brizendine, MD. The Female Brain. New York; Morgan Road Books, 2006.

6. Environmental odor intolerance in pregnant women

7. Treatment options for nausea and vomiting during pregnancy

8. Mother-infant skin-to-skin contact after delivery results in early recognition of own mother's milk odor

9. Olfactory stimulation in the relationship between child and mother

10. Mothers' recognition of their newborns by olfactory cues