J. Allen wrote:
I've been thinking about this for a little while. As living organisms, we have to consume in order to convert that sustenance into energy and to power our bodies. Why, though, do we eat other life forms? We eat plants and animals. Why? Why are we designed this way?
Because existing life contains the proteins and nutrients that other life needs in nice, neat packages. You've evolved this way because it is more efficient for your body to consume these elements already manufactured rather than needing to manufacture them yourself. Lower life forms (such as bacteria) can consume the raw elements (rocks, dirt) and create biological elements that they can use. However, being simpler, they don't need to produce as many.
More complex life forms need a lot more chemicals, organic compounds that just don't exist in nature. They need to either manufacture from raw Earth materials or obtain them from life forms that already created them. It's easier to just eat another form of life to get them.