Using an individual-based and genetically explicit simulation model, we explore the evolution of sociality within a population-ecology and nonlinear-dynamics framework. Assuming that individual fitness is a unimodal function of group size and that cooperation may carry a relative fitness cost, we consider the evolution of one-generation breeding associations among nonrelatives. We explore how parameters such as the intrinsic rate of growth and group and global carrying capacities may influence social evolution and how social evolution may, in turn, influence and be influenced by emerging group-level and population-wide dynamics. We find that group living and cooperation evolve under a wide range of parameter values, even when cooperation is costly and the interactions can be defined as altruistic. Greater levels of cooperation, however, did evolve when cooperation carried a low or no relative fitness cost. Larger group carrying capacities allowed the evolution of larger groups but also resulted in lower cooperative tendencies. When the intrinsic rate of growth was not too small and control of the global population size was density dependent, the evolution of large cooperative tendencies resulted in dynamically unstable groups and populations. These results are consistent with the existence and typical group sizes of organisms ranging from the pleometrotic ants to the colonial birds and the global population outbreaks and crashes characteristic of organisms such as the migratory locusts and the tree-killing bark beetles.

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June 1st. Has passed five quarts of urine. June 2d. Six quarts. Increase each dose of iron to twenty minims. June 3d. Patient was put on house diet, and sulphate of cinchonia, three grains, in a pill, before each meal was prescribed ; the iron to be continued after meals. June 4th. Reports that he has no sensible, perspiration. No sensitiveness in region of kidneys. "Urine pale; specific gravity 1010 ; a very little sediment, consisting of a few pus corpuscles and a little bladder epithelium. Indican normal. Urophain, urea, earthy and alkaline phosphates diminished. A slight trace of albumen." (Dr. Wood.) June 5th. Has passed seven pints of urine. Feels generally better. June 6th. Six pints of urine. June 7th. Same. June 8th. Seven pints. June 9th. Seven pints. Is gaining strength. Substitute compound tincture of gentian, two fluid drachms before each meal, for the cinchonia. On the 10th two fluid ounces of infusion of jaborandi were ordered, to be given at once and repeated in an hour. June 11th. Perspired profusely for two hours, and vomited three or four times. Urine reduced to three pints. June 12th. Urine six pints. June 13th. Repeat jaborandi. June 14th. Urine three pints. Perspiration very profuse. Appetite impaired. Omit medicine. Ordered elixir of phosphate of iron, quinine, and strychnia, one fluid drachm before each meal. June 15th. Has had no sweating. Urine three pints. June 16th. The same, but feels stronger. Urine four pints. June 17th and 18th. Four pints of urine each day. June 19 th to 23d. Five pints each day. Jaborandi was again administered on the 23d. June 24th. No sweating or nausea reported. Urine six pints. Metcalf's fluid extract of jaborandi was substituted for the infusion, in doses of ten drops every hour, until profuse sweating was produced.