Why Elephants Don’t Explode: How Nature Solves Bigness | Hacker News Reader

Why Elephants Don’t Explode: How Nature Solves Bigness

noticing.co

99 pointsaaossa30 comments

This reminds me of an old (1928) piece titled "On Being The Right Size" by JBS Haldane [0], which lightly touches on many different concerns related to sizing:

> Of course tall land animals have other difficulties. They have to pump their blood to greater heights than a man, and, therefore, require a larger blood pressure and tougher blood-vessels. A great many men die from burst arteries, greater for an elephant or a giraffe.

https://irl.cs.ucla.edu/papers/right-size.html

I'm confused by the slider task. The explanation simply says that voles eat much more than elephants per unit of body mass, but the sliders suggest that voles literally eat more food per day than elephants.

Are the grass pictures supposed to be interpreted relative to the size of the animals next to them?

Yes, the article seems to be mostly a roundabout restatement of Kleiber's Law [1]

[1] https://en.wikipedia.org/wiki/Kleiber%27s_law

Yes.

> 402

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Don't see many 402s!

Also, D3 is awesome. Don't pay to show a graph, either draw it in any visualization tool and take a screenshot for the article, or use locally hosted D3.

Here's another fun read on why sizes matter as it relates to monster movies

http://fathom.lib.uchicago.edu/2/21701757/

This is a great link -- thanks for posting!

I visited San Diego Zoo a few months ago. In SDZ's Safari park, they host one of the biggest elephant park in North America. I remember the tour guide mentioned Elephants are so huge that if you lay down for more than 4 hours, there are pretty high chance they won't stand up and eventually leading to death due to the size of their body.

"Elephants in zoos sleep for four to six hours a day, but in their natural surroundings the elephants rested for only two hours, mainly at night." [1]

[1] http://www.bbc.com/news/science-environment-39126993

This article is interesting, but all it talks about is why big animals have a lower metabolic rate than small ones. I wish it would have also addressed the question of why small animals have a higher metabolic rate than big ones. If elephants can get away with having such a low metabolic rate, why can't voles?

That's what the article is all about. It's temperature management. Smaller warm-blooded animals have less mass to generate heat and higher surface area to volume ratio to dissipate it faster. They need a much higher metabolic rate to maintain body temperature, especially when the environment is very cold. They would freeze if they had the same rate as the elephant.

Large warm-blooded animals have more mass generating more heat and less surface area to dissipate it. They need a much lower rate or they would overheat. Not to mention the objectively huge amount of food and air circulation that would be required to maintain that rate.

If either animal had the other's metabolic rate, it would be dead within hours, if not minutes.

Couldn't smaller animals just evolve better insulation instead? Surely it would be easier to survive if they didn't have to eat so much.

Evolution doesn't pick the optimal solution, it just weeds out the solutions ones that aren't good enough.

Nature's insulation is fat and fur/feathers but there is a limit to how much that can help. It adds weight and bulk - hummingbirds have to hover their own weight so adding more fat is like making bigger rocket: you need more fuel to lift your fuel.

More insulation has other tradeoffs. Look at arctic animals - they're not very agile or dextrous. Penguins, whales, sealions, polar bears... they're all 'lumpy' and nowhere near as agile as other areas. Even the occasional agile animal like a snow fox is 'lumpier' than its temperate brethren, but they only have to be more agile than the tubes of fat that hunt them.

Any time you think "why didn't this or that feature evolve a different way", have a think about tradeoffs in terms of survivability.

The article claims "Without its internal heaters turned up to-the-max, a shrew would leak out all of its heat and freeze. And this explains its furious appetite."

If I was to hazard a guess, it's because the vole has a lot more competition for food. The elephant's main risk is eating up all the food and having none left. The vole's main risk is having some other animal grab the food first. At the vole's size, and with the vole's eating strategies, there's a real advantage to being quick. With the elephant and similarly sized animals, not really (and also, there's the exploding problem).

There's also the problem that a skeleton doesn't get stronger at the same rate that a body gets heavier, so a larger animal is going to have to avoid rapid accelerations in order to not break its bones or sprain its ligaments.

I think it relates to the surface area:volume ratio. The implication is that a smaller animal will have a relatively higher surface area to lose heat to, thus necessitating increased metabolic rate to make up for that loss.

http://www.tiem.utk.edu/~gross/bioed/bealsmodules/area_volum... provides some good basic info

I thought this would be about allometric scaling of organs. But if we're on the topic of metabolism, I wonder what the rate of cancer is for shrews vs. elephants, once the metabolism and lifespan are somehow accounted for.

This is actually a great question - take a look at this discussion from 2015.

This isn't my area of expertise, but my understanding is that elephants have many more copies of TP53, a gene that plays a critical role in regulating the cell cycle (and thus uncontrolled growth that may occur in cancer).

One of the linked papers also states that there was no correlation between body size and cancer in their experiments.

https://www.nature.com/news/how-elephants-avoid-cancer-1.185...

Cancer is vastly more common among specific tissue types. So, it's hard to do a direct comparison.

What does metabolism have to do with cancer?

Quite possibly, a lot:

https://www.nytimes.com/2016/05/15/magazine/warburg-effect-a...

https://en.wikipedia.org/wiki/Warburg_effect

That was hard to read. Would have been much easier if they just got to the point.

Geoffrey West's book Scale gets into this -- good read.

https://www.amazon.com/Scale-Universal-Innovation-Sustainabi...

Also, at the cell level, large animals should have a better self-protecting mechanism against cancer, because more cells means a higher probability of cell-divisions going awry.

The difference in metabolic rates between large and small animals is directly linked to why large animals typically have longer lifespans the smaller ones.

Since the embedded plot isn't showing up, you can see it at https://plot.ly/~aatish/115/an-ounce-of-a-smaller-creature-g...

Knut Schmidt-Nielsen wrote a couple of books on this topic. Googling Bonner and Schmidt-Nielsen together seems to bring up some surveys of the literature.

Volume vs area, basically.

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