Normal or natural human longevity is ~30-35 years. You can determine that because it is essentially a function of (average) body weight. The bigger your (specie

Normal or natural human longevity is ~30-35 years. You can determine that because it is essentially a function of (average) body weight. The bigger your (species) is, the longer you live. Really interesting book on the subject: https://www.amazon.com/Sex-Origins-Death-William-Clark/dp/0195121198 https://www.amazon.com/Sex-Origins-Death-William-Clark/dp/01... TLDR: 2 unchangeable sexes + death (both of those) has proven to be the most effective reproductive strategy, beating out every competitor by a huge margin. This means there is a very good reason for death to exist and death is a "new" thing. There was a very long time when animals (well ... technically multicellular bacteria colonies) just didn't ever die. Some of those are alive right now and are hundreds of thousands of years old, at least. We know about the effectiveness because there are species (none are animals) that are still alive that predate evolution's "invention" of death, that have competed to conquer the earth, and they failed dismally. And we know about the 2 unchangeable sexes because there's a lot of variation in sexes, none very successful (there even are asexual animals, and animals that can change their sex, and animals with different sex arrangements. Some have small differences (like males giving birth), and some are hugely different, like true asexual animals)