I brought two top Silicon Valley entrepreneurs working on extending lifespans on the Newcomer podcast this week. One of them is trying to help people live longer. The other, their dogs. James Peyer, the CEO of Cambrian Bio, is acquiring majority stakes in drugs that could combat a particular illness while showing promise for broader use among healthy humans. Meanwhile, Celine Halioua, the CEO of Loyal, is developing drugs to make dogs live longer. Fundamentally life extension, or longevity, is about finding drugs and treatments that can be given to healthy humans to help them live longer, healthier lives. Instead of just treating illnesses, entrepreneurs in the space want to find ways to stave off aging in already healthy people. The space has long been a fascination of mine. In February 2022, I profiled Elad Gil’s investments in an array of companies looking to make healthy humans live longer, healthier lives. The HBO show Silicon Valley helped popularize the idea that Silicon Valley elites were pumping their veins with younger people’s blood. (I’ve yet to get anyone to confess to me that they’re buying plasma.) To the chagrin of this week’s guests, one tech mogul desperate to avoid death has received a lot of the attention recently. That’s Braintree founder Bryan Johnson. Time magazine just profiled Johnson under the headline “The Man Who Thinks He Can Live Forever.” Johnson, 46, is a centimillionaire tech entrepreneur who has spent most of the last three years in pursuit of a singular goal: don’t die. During that time, he’s spent more than $4 million developing a life-extension system called Blueprint, in which he outsources every decision involving his body to a team of doctors, who use data to develop a strict health regimen to reduce what Johnson calls his “biological age.” That system includes downing 111 pills every day, wearing a baseball cap that shoots red light into his scalp, collecting his own stool samples, and sleeping with a tiny jet pack attached to his penis to monitor his nighttime erections. Johnson thinks of any act that accelerates aging—like eating a cookie, or getting less than eight hours of sleep—as an “act of violence.”  Even as Johnson is getting a lot of attention for his self-experimentation, there’s a growing view that there could be something credible behind Silicon Valley’s interest in life extension. The Economist just wrote that “slowing human ageing is now the subject of serious research.” Many in mainstream science and medicine look at all this slightly askance. That is understandable. It is an area which attracts chancers and charlatans as well as those with more decent motives, and its history is littered with “breakthroughs” that have led more or less nowhere. America’s Food and Drug Administration does not recognise “old age” as a disease state, and thus as a suitable target for therapy. Nevertheless, evidence has been accumulating that such research might have something to offer. Some established drugs really do seem to extend life, at least in mice. That offers both the possibility that they might do so in people and some insight into the processes involved. The ever-greater ease with which genes can be edited helps such investigations, as does access to large amounts of gene-sequence data. The ability to produce personalised stem cells, which stay forever young, has opened up new therapeutic options. And new diagnostic tools are now offering scientists means to calculate the “biological ages” of bodies and organs and compare them with actual calendar ages. In principle this allows longevity studies to achieve convincing results in less than a lifetime. I dug in with Halioua and Peyer about where they saw the most opportunities, how their own companies were progressing, and why they thought Johnson’s publicity campaign was doing a disservice to companies working on longevity. The duo helped break down the space, discu