Abstract
All living organisms need to consume nutrients to grow, survive, and reproduce, making the successful acquisition of food resources a powerful selective pressure. However, acquiring food is only part of the challenge. While all animals spend much of their daily activity budget hunting, searching for, or otherwise procuring food, a large part of what is involved in overall nutrition occurs once the meal has been swallowed. Most nutritional components are too complex for immediate use and must be broken down into simpler compounds, which can then be absorbed by the body. This process, digestion, is catalyzed by enzymes that are either endogenous or produced by the host's microbial population. Research shows that the nutritional value of food is partially constrained by the digestive abilities of the microbial community present in the host's gut and that these microbes rapidly adapt to changes in diet and other environmental pressures. An accumulating body of evidence suggests that endogenously produced digestive enzymes also have been, and still are, common targets of natural selection, further cementing their crucial role in an organism's digestive system.