Venki Ramakrishnan
speaker
313 appearances
2 recordings
2 series
first heard Sep 2024
last heard 25 Apr
Venki Ramakrishnan’s voice in public audio — every appearance, attributed to the second.
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recordings per month · last 12 monthsRecordings per month over the last 12 months — 1 in all, peaking in Apr 2026 with 1.
Appearances
For example, companies or societies, cities, they all grow and they age and then they die. So in our case, what do we mean when we die? It's a particular weird thing. It has to do with us as an individual, and that's also hard to define. What do you mean by an individual? Because the strange thing is, When you're alive, millions of cells in you are dying all the time.
And in fact, many of those cells are required to die at appropriate times. If they didn't die, you as an individual would die. So that's one side of the story. The other side is that when you die, most of the cells in your body are still alive. In fact, that's the reason why we can donate our liver and kidney and heart to transplant recipients when we die. And so here you have this paradox.
When you're alive, a lot of you is dying. When you're dead, most of you is still alive. So what does this mean? It means that we can no longer function coherently as a whole individual. And we worry about it because we are aware of ourselves as an individual. We have consciousness. But you can imagine species that don't have consciousness.
The extreme are, for example, plants, but also simple animals. They might never actually, even if they had a nervous system, they might not actually even think about death. It's just something that happens. So it's a peculiar situation that we're in that we obsess about mortality and death.
Oh, definitely. I think, for example, when you get to sexual organisms, then you have a clear separation between the germline, which is responsible for reproduction, and the rest of the body. And in a sense, there's a part of us that has been alive for billions of years because we didn't come out of nothing. We came out of a cell, which came out of a cell, which came out of a cell.
So there's a direct lineage all the way back to a few billion years that did not die. And so the germline, there is a chapter in my book which is called, I think, the immortal germline and the disposable body or soma. And so that is really a dichotomy in complex organisms. And in a way that's different from say bacteria or other organisms.
And what is interesting is that germlines aren't actually immortal, but we've evolved so that germlines are much better protected. For example, DNA damage or other kinds of damage are cause of aging. And germlines are protected much better against DNA damage and other kinds of damage. The other thing that happens is that germlines are selected almost ruthlessly.
For example, when a female fetus, in the early embryonic stages, there are almost a million eggs or so. But of course, you know, you don't have, those million eggs are not, you don't have a million ovulation cycles. You know, in a human woman's life, maybe a few hundred eggs are, you know, secreted during menstruation, I mean, during ovulation. So what happens to all the others?
Well, the others are all ruthlessly selected because There's a whole process of selection from the oocyte, the precursor of the egg, all the way to the final egg that ends up ready for fertilization. And at each stage, it's monitored for defects and ruthlessly pruned out. And of course, sperm in males is also ruthlessly selected for, you know, millions of sperm and they all have to swim.
And if they can't make it and they are in any way defective, they just don't have a chance to undergo fertilization. And even after the embryo is formed, many embryos spontaneously abort without the mother even being aware of it in many cases. Some cases they are aware if it's later and there's a miscarriage. And so there's ruthless selection there.
And even within the developing embryo, defective cells are destroyed. So I think this... I thought about why is it that we get old, but when a child is born, it's not born old. So it's as if the biological clock has been reset every generation. And that's because of this combination of protection and against damage for the germ cells and ruthless selection.
I think it's that combination that allows us to have an embryo that is, you know, looks, you know, it's gone back to state zero. But of course, all of the little tags on the DNA have been erased. These tags are markers for aging. They've been erased and and then reprogrammed to start from scratch.
So so it's all this combination of things that goes on to to reset the the biological clock every generation.
Yeah, so this has to do, you know, we talked about how some species live only a day or two and others live several hundred years. Well, you know, Jeffrey West, who we both know from Santa Fe, has written a great book called Scale. And in that book, he talks about relationship between lifespan and parameters like size.
It turns out that large mammals live, on average, much longer than small mammals. Now, why would that be? Well, it's because evolution simply doesn't care how long you live. It cares about fitness, which is how likely are you to pass on your genes? How successful are you going to be at passing on your genes? And so I think...
If you're a mouse, there's no point in spending a lot of resources to repair and maintenance because we do have sophisticated repair and maintenance mechanisms. Otherwise, we wouldn't even last a year. We would be dead before that. We do have this very sophisticated mechanism, but that takes energy and takes resources.
And in a small animal, it's not worth it because the animal is going to be killed off by a predator or die of starvation or some other cause. So there it's more advantageous for evolution to put resources into rapid growth and reproduction. And that's what a mouse does. And at the other end, you have things like a bowhead whale or a Greenland shark, very slow metabolism and
well, especially the Greenland shark has a very slow metabolism, large, and can produce offspring over a long period. So you have these opposite extremes. And the interesting twist on this are bats. So bats weigh about the same as a mouse, the same size as a mouse, but can live 10 to 20 times as long. And the reason is bats can fly, so they can escape predation.
And they also can forage over a much wider area and are less likely to starve. So it makes perfect sense that you would have this evolutionary thing.
This is called Pitot's paradox, after Pitot, who was the scientist who first formulated it. Because an animal like a whale or an elephant has thousands of times more cells than a mouse.
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