In Part I we were talking about how our biology as human animals influences breastfeeding. Understanding the evolution of our species helps to make sense of why your baby behaves as he does and hopefully will guide your responses to be more in harmony with his needs (and therefore have a happier baby!).
It's estimated that we humans became a separate species about 1.5 million years ago. The advent of agriculture, and hence, civilization, occurred only about 10,000 years ago. Our species has spent 99% of its existence in a hunter-gatherer type lifestyle. That means that for most of human history, babies fed only on their mothers' milk. Supplementation by other species' milk probably occurred once animals were domesticated, but pastoral living did not pre-date agricultural by very much. We can infer from the studied behavior of hunter-gatherer groups still around in the last couple centuries that their infants were with their mothers constantly - carried during the day and sleeping together at night - and fed on-demand around the clock. Indeed, babies who demanded this high level of attention were more likely to survive and not be carried off by a lion!
In addition, the natural age of weaning for a human infant is probably much later than is practiced in western culture - probably between 2.5 and 7 years! Research on cultural groups around the world, age of weaning in other primates, and human skeletal remains supports this. Only in the west are babies weaned before one year of age, and most nurse for several years still today. The drive to suckle continues throughout the first several years, as anyone who has seen a three year old with a pacifier stuck in his mouth can attest. Human infants evolved with breastmilk as their primary or sole food until about two years of age, and then gradually weaned over a period of several years. (This research is well documented and a few minutes of googling will unearth numerous sources.) There are many reasons why human infants would have evolved this feeding pattern including inconsistent availability of foods during the millions of years we spent as hunter-gatherers, protection from predation, nutritional efficiency, and bonding in a social species.
From a nutritional standpoint, you should breastfeed as long as you can and are comfortable doing so. The WHO recommends breastfeeding for two years or more. Studies show many benefits of breastmilk for babies, and the longer babies are breastfed, the more they benefit.
The mechanics of the breast and lactation also indicate feeding on demand is appropriate. The more the baby suckles and empties the breast, the more milk is produced. It's a supply and demand operation. Nursing as often and as long as your baby wants, especially in the first few months, ensures you have an adequate supply of milk. When baby goes through growth spurts, he may nurse even more, bumping up your supply and making you hungry, thirsty and tired.
The first milk that comes out of the breast at each feeding is called foremilk. This is milk left over from the last feeding. As the milk sits in the breast between feedings, fat is reabsorbed into your body, so foremilk is lower in fat content. It's more hydrating for the baby, but less satiating. The fattier hindmilk that comes out after baby has been suckling a while makes him feel full and satisfied. The more frequently you nurse, the more fatty milk your baby gets because the fat hasn't reabsorbed yet. Babies who are put on a schedule and only allowed to nurse every few hours may get a bigger volume of liquid at once, but it won't be as filling. Sometimes if baby is crying after a nursing session, mom may assume she doesn't have enough milk when in reality, baby is not getting sufficient fat content to stay full.
We're going through a bit of a difficult phase around here at the moment. I think my little cherub is about to pop out her first tooth! As a result she has reverted to only napping in 15 mintue intervals and waking about 20 times every night. At any rate, she is demanding my attention right now and trying to "help" mommy type, so I'm going to wrap up Part II and come back to talk about my own breastfeeding experience next time!