(highlight:: Mammals Have, On Average, the Same Number of Heartbeats Over Their Lifetime
Key takeaways:
• From a physicist's point of view, there was no theory on why humans live up to 100 years.
• A theory on aging and mortality must predict 100 years for humans.
• Understanding what keeps a system going is crucial to figure out what goes wrong with it.
• Metabolism is essential for organisms.
• Mammals have an average number of heartbeats in their lifetime.
Transcript:
Speaker 2
Mammals have on average the same number of heartbeats in their life. Whether you're a human or a horse, a whale, or a shrew or a mouse, when we get back to this sort of hard physics view of biology, that seems extraordinary to me.)
- Time 0:08:18
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(highlight:: The Fascinating Relationship Between Metabolism and the Weight of an Animal
Key takeaways:
• Metabolism is the amount of energy needed to keep an animal alive.
• There is a simple relationship between metabolic rate and an animal's size.
• Doubling an animal's size does not require double the amount of food, but rather a 75% increase.
• There is an extraordinary economy of scale with increasing size, resulting in greater efficiency.
Transcript:
Speaker 1
Metabolism, of course, is fundamental because it's fundamental to any system. What is metabolism? It's the amount of energy needed to be supplied per second or per minute or per day to keep you alive. So roughly speaking, you can think of it as the amount of food you need to eat per day to sustain yourself and do all the various things that you have to do to persist. And what is extraordinary? And this has been discovered in about 1932 by a biologist named Max Clymer. And what he did is he simply took values of metabolic rates that had been measured on various animals. And then he did his own experimentation, measurements on other animals. And then he just plotted the metabolic rate as measured versus the size of an animal as represented by its weight. And he found that there was this extraordinary, yet very simple, systematic relationship between them. And our first, let me summarize it in English. It says, if you double the size of an animal, or to put it slightly differently, if you look at an animal that's twice the size of another. And let's just keep it for mammals again, for simplicity. If you look at a mammal that's twice the size of another, what you might expect is that it would require twice as much food to stay alive. We would need twice the metabolic rate because there's twice as many cells. But in fact, what he discovered was that you don't need twice as much. You only need very roughly 75% as much. What's crucial to understand, you can double from any value to another value. So it's whether you go from two grams to four grams, 20 grams to 40 grams, 40 kilograms to 80 kilograms. It does about double anywhere. And you always have the same roughly 75% increase. That is, you save. Another way of talking about it is you save 25% every time you double. So there's this extraordinary economy of scale, if you like, this extraordinary efficiency and systematic efficiency that develops with increasing size. So you are much more efficient than your dog. And your dog is more efficient than your cat. And the cat is more efficient than the mice it chases. But your horse is more efficient than you in this sense in terms of the amount of energy needed to supply each cell.)
- Time 0:12:40
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(highlight:: The Number Four Determines the Biosphere Around Us
Summary:
Logarithmically, all kinds of physiological quantities line up very closely on a straight line. They all have slopes that are simple multiples of the number one quarter. So to boil all this down into something extremely simple, it says that in terms of the way nature scales from the smallest to the largest, it's completely dominated by this extraordinarily simple number One Quarter.
Transcript:
Speaker 1
But what followed after that is things you've already alluded to, people started measuring lots of other things and plotting them this way, namely, logarithmically, all kinds of Physiological quantities, like something as mundane as the length of your aorta, the aorta is the first tube that comes out of your heart. So the length of the aorta versus weight, plotting things like thing we've already talked about, life spans, number of children, number of offspring. So both physiological quantities, and you plot them this way. And what is remarkable is they all look like what I just described for metabolic rate when you plot some logarithmically, they line up very closely on a straight line. And here's the other big kicker. They all have slopes, just like metabolic rate that are simple multiples of the number one quarter. So just to give you a couple of examples, heart rate decreases with body size, the shrews bridging at over 1000 times a minute, the whale is only beating at less than 10 times a minute. That follows, if you plot them, plot all those numbers, the slope of that line is one quarter, actually it's minus one quarter, the minus just that symbol for it's decreasing with size, But the slope is 0.25 approximately, and so on. So to boil all this down into something extremely simple, it says that in terms of the way nature scales from the smallest to the largest, it's completely dominated by this extraordinarily Simple number one quarter. The number four is actually determining basically the biosphere around us. So this begs the question, where the hell does this number four come from?)
- Time 0:19:34
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- [note::Scaling Graphs: https://twitter.com/bhcomplexity/status/1621379813427793920?s=49&t=pWPlPkE-SmCUmYrqJkZ3Ng]

(highlight:: Scaling is the study of how complexity systems respond to changes in size
Summary:
And really what scaling is, and I never understood this, this moving from one size to another until I read it in your book, is it's fundamentally, isn't it the study of how complex systems respond to changes in size?
Transcript:
Speaker 2
And really what scaling is, and I never understood this, this moving from one size to another until I read it in your book, is it's fundamentally, isn't it the study of how complex systems Respond to changes in size?)
- Time 0:22:27
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