.@jacobkimmel thinks that the functionality to reverse aging already exists in our epigenome. But then why didn't evolution already optimize for longevity? Jacob explains that if you consider evolution as an optimizer, the gradients flow in a really surprising way. Naively, it seems like evolution should want you to live longer (more time to have babies and care for your kin). Jacob explains 3 complications on the naive picture: 1. Baseline mortality was brutal throughout most of history. Even without aging, you'd likely die from infection, predation, or accident before reaching 50. So there's no signal flowing back from 100 to the genome which incentivizes some selective process to make you live longer, even if it was easy to do. 2. There's selection against fixing just one (but not at all) causes of aging). Because then you have some grandpa who's slightly healthier but still a worse use of resources than the next generation from the gene's eye point of view. 3. Evolution is very limited as an optimizer. The step size (number of variants you can test in parallel) is limited by your step size. And through the most of history, this bandwidth was dominated by selective pressures much more urgent than de-aging (for example, building a better immune system to fight infectious diseases). Full episode with @jacobkimmel out Thursday. So excited about this one. Jacob's simple 3-point list led to more than half an hour of random digressions, from how many antibiotics were naturally evolved, to how hard evolution actually optimized for intelligence, to how we can actually detect the evidence for some deadly ancestor of HIV in our genome.