Would there be so many billions if we didn't figure out how to convert petroleum into fertilizer and so many other useful things? My point is that, just because we now have billions, it feels wrong to justify maintaining those billions of people at the luxury levels so many of us enjoy. We differ from other animals only by degrees, not by kind. From watching so many nature documentaries over the years, and reading nonfiction books about animals, I understand many mammal newborns don't make it into childhood. I'm not convinced that a high human infant-mortality rate is bad. It just feels bad, and with our pathological focus on feeling happy and suppressing sadness, a consequence seems to be we make decisions out of momentary selfishness rather than care for future generations long after we individuals are dead.