This is a remarkable new paper on aging that lots of researchers are getting excited about. Basically, they give blood plasma from young rats to old rats, and then measure the effective biological age of the treated old rats against a group of untreated old rats. They use an innovative way of measuring age by developing 6 new “epigenetic clocks” that allow them to quantify the aging process in a rigorous way that can work across species. The results of the treatment are absolutely phenomenal, with the old treated rats looking mostly like young rats 155 days later! The treated old rats can escape from a maze much faster than regular old rats, and their tissue (liver, brain, heart) looks much younger when stained to reveal signs of aging (senescent cells). Not only does it stop aging, it actually reverses it! Amazingly the converse is also true— if you put old blood in young rats, it causes them to age much faster. If this works in humans as well, which I’m guessing it does, it seems like a huge deal. Rich people will start replacing their blood plasma with blood from young people and stay young for decades longer, amassing even more wealth and influence. Society will probably pass laws preventing parents from selling their kids’ blood (or using it themselves!). Aside from these dystopian fears, I find it funny that something so ludicrously simple and silly sounding actually works and might in fact be the “fountain of youth” long sought for.