A new set of simulations involving happiness, longevity, and population shows that when different isolated groups join together to form a larger, competitive group, population may be traded for longevity except when growth rate is the only difference.
Recall that longevity is the time it takes for a group to begin disabling the habitability of its environment by consuming species that keep alive the species it directly depends upon for survival, and that my calculations show that humanity recently reached that point. The simulations indicate that world history can be approximated by a lot of isolated groups, which is also equivalent to what would happen if isolated groups came together and allocated resources equally among them. If the world instead had competition among its subgroups for resources, then the average population over history would be smaller (such as 50%), and longevity would be longer by the same fraction (150%); happiness would have dropped only slightly (3%).
In general, any differences between isolated groups in population or per-capital consumption of ecological resources (footprint) will translate into differences in power to acquire resources and convert them into personalized environments. Those power differences will result in a loss of population when the groups are merged and they must compete for resources with too few available for some people to survive when the resources are allocated according to power. Having fewer total people enables those who are left to consume resources for longer at their current rates, thus increasing longevity. This is not the only way to increase longevity, though: by decreasing consumption rates, longevity can be increased without an accompanying drop in population.
Ironically, any growth at all ensures that a group's longevity will eventually reach zero. Pursuing more longevity, while insisting on growth, is therefore a trap. Even if we use the increased longevity to find more resources so we can accommodate more people, we will be forced to adjust and eventually limit the growth rate of consumption based on physical constraints of speed and availability of resources. To pursue more longevity and accept loss of life as its cost is to automatically assume that the casualties have less value than the survivors or their potential replacements.