Transcription
So, so I heard long ago and I checked it out and I think it's true that all mammals live for about the same number of heartbeats except for humans who live two or three times that. Except if you go back far enough in time when we were just living in caves, we were right with all the rest of the mammals. So, first, is that true? Second, there are animals, not mammals, that live much longer than we do. I'm thinking of the Gopagus tortoise, for example. Yeah.
>> So do you guys study other animals to get insight?
>> So there is a whole field devoted to looking at lifespan of different species and uh you are right that at least among mammals Jeffrey West who's written a book called scale shows that the number of heartbeats is is roughly the same. That has to do with the fact that smaller animals have a higher metabolic rate. They have a faster metabolism and and they almost need to because their surface to volume ratio is larger. They dissipate heat more.
>> We did a whole explainer on surface to volume ratio.
>> So they they they need to maintain a higher metabolic rate. Uh that's one of the reasons.
>> Well, that's only one of the reasons why they have higher heart rate. That's not a reason why they should die sooner. Ah the why we should die sooner is has an evolutionary explanation and that is evolution doesn't care how long you live. It only cares about fitness. Fitness in the biological sense is the likelihood that you're going to be able to successfully pass on your genes.
>> And people always misinterpret that as being physically fit or stronger or whatever.
>> Survival of the fittest as in I'm in great shape.
>> Yeah. Darwin should have found a different word.
>> So evolution cares about fitness. Now at the same time for most of our history and certainly the history of all other species, resources are limiting. And so you have to select do you put more of your resources into maintenance and repair of the individual animal or do you put it into growth and reproduction? There's always a balance if you if you have limited energy. So, in the case of a mouse, which lives about two years in the wild, uh there's no sense in having a mouse live for 40 years because long before that, it's going to be eaten. Yep.
>> Exactly. You beat me to or it'll die of starvation or drought or something. And so in the case of a mouse, evolution has favored selection of a species that grows very quickly and reproduces prolifically. That's a mouse. If you get to a large animal like a boowhead whale, let's take a even even bigger than an elephant, they can live for two 300 years. And they have a very relatively slow metabolism.
>> Wow.
>> An even slower metabolism is not a mammal, but it's still a vertebrate called the Greenland shark. 700 years.
>> Wow. Listen to that. Yeah.
>> A vertebrate living for 700 years. Very slow metabolism.
>> Wait, wait, wait, wait, wait. How do you know that? We didn't even have marine biology 700 years ago.
>> So, how they they can do things like carbon dating and
>> they cut one open. It was 700 rings
>> inside. I mean, you've got on just
>> No, no, no, no, no. So, you've got the mayfly lives a day.
>> Mayfly lives a day,
>> right? And then between that, you've gone from there to a Greenland shark and your Galapagus.
>> Other animals that are thought not to even age biologically.
>> What's the immortal like the hydra and the immortal jellyfish? These things are
>> there's an actual animal called the hydra.
>> Yes. Awesome.
>> Not just in in
>> not just in GI Joe.
>> No. Oh, no. Marvel.
>> No, no, no. In in in legend.
>> Oh, you mean the real hydra?
>> This is a freshwater small animal. and and they're full of stem cells, so they're constantly regenerating themselves. But if you followed an individual, it would also age only very slowly. It's just in the wild, it it it dies for other reasons before actually aging.
>> So, so there's a whole range. Now,
>> so humans might be the only species that dies of natural causes in the world. I mean, if you want to think about it that way,
>> possibly, you know,
>> we're apex predator.
>> Yeah. So
>> yeah, I think that may be true. In fact, there's a book uh written by Steven Ostad called Methusela Zoo, which where he talks about all these animals. In this book, he he points out
>> Methusela Zoo
>> in Methusela Zoo. He points out how all these species have such different lifespans. And it's because of this evolutionary selection. But it's actually worse than that. It's the fact is evolution will select for things that help you early in life
>> even if they cause a problem later in life. So many of the things that cause aging are related to growth
>> for example or to cancer prevention you know prevention of or the or scinesscent cell creation these things all help us early in life
>> and they're they're a problem later in life but evolution doesn't care what happens to you when later in life
>> when not making babies. Correct.
>> Exactly. Yeah. cuz that's the whole deal.
>> So what helps us survive in infancy and then go on to reproduction is the key component of our decline and demise.
>> Not always, not everything. There are things that happen to us early in life that are selected for early in life that cause aging.
>> So the real deal is just keep having babies your entire life. Uh and then you you you'll never age. However, you will eventually kill yourself because of these kids. So, so we're we're an outlier. We're an outlier. We live about twice as long
>> twice
>> as we would based on our size,
>> but only post caveman life, right?
>> Um 40,000 years.
>> Exactly. So only I mean half of everyone died by 30
>> and so we're not 2x other mammals at our size.
>> Yeah. And one last thing is there's a group of animals, mammals, the bats. They live much longer. They're about the same size as a mouse in in terms of mass.
>> Yeah, you flee a mouse.
>> They they they live about 10 or 20 times as long as a mouse.
>> And the reason is they can fly around. So that means two things. They can escape predators more easily.
>> And they can also forage over a much wider area for food.
>> And and when they roost, they roost in the ceilings of caves. So they're not as accessible to predators.
>> They've been designed to survive longer. And so there it's worth it for evolution to make them live longer because they'll still keep producing more babies.
>> Yeah. So you got to be grandpa monster is basically the deal.
>> That's what grandpa from the monsters.
>> Grandpa from the monsters if you want to live long.
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