What density-dependent growth limiting factors kept the human population relatively low prior to the advent of agriculture?

Limited food supply and competition

Explanation:

Density dependent factors are those which in general lead to reduction of growth rate of population when the population density increases. One of such factor is availability of food and competition.

Whenever the density increased to an extent where the resources or available food becomes scarce or limited,then the growth rate of population decrease.  These factors generally lead to logistic growth pattern of population.  

where in your body is there an enzyme that does function at a high or low ph? what is the name of that enzyme and its function?