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Comment by hyperdunc | Hacker News Reader

Then I guess the obvious question a non-physiologist would ask is, why don't all our muscles already have vast amounts of mitochondria? If it's that beneficial with no major downsides then surely evolution would have stumbled on that configuration already?

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Because the trade-offs are not optimal for most people. Might require huge caloric budgets not available (until now). At present, energy efficiency is actually detrimental to reproduction for most people in first world countries, so it's conceivable if we wait another million years or something, our muscles might have a lot. Assuming not getting tired leads to reproductive success, of course.

For a vast amount of human history food has been much harder to obtain and less calorie-dense than it is today, so evolution has optimized for energy efficiency rather than raw power.

Do chimps/apes have a greater muscular power-density than humans?

Significantly, and a large part of the reason why is energy efficiency. Humans have large brains that take a lot of calories to sustain, and because of their large brains didn't have nearly as strong evolutionary pressure to maintain musculature.

Probably the wrong way to look at it. They can exert greater force for shorter periods but the great apes have far worse endurance than humans. A chimp is about a third stronger than a human of equivalent weight but we can run marathons and they can’t. We have a higher proportion of slow twitch muscle fibres compared to fast twitch than the great apes.

I think the major downside is energy costs. You can only support so much high-energy tissue with a constant caloric budget.

Think of evolution as Uncle Fester from the Addams Family.

You never know quite what you'll find him working on, but every now and again, he'll have just the thing for the job.

But by and large, it's most likely something completely insane. Evolution has no intent. No direction. It's more a descriptive statement of an ongoing process than a end to which some force is constantly seeking.

Mitochondria do produce a lot of free radicals. Probably energy expensive to maintain cells like that.

not only energy expensive but free radicals do genetic damage, and a this requires the second budget for a set of enzymes to counteract the damages and scrub out FR's

Why isn't Heart Cancer more common if it's producing so many free radicals? Are there other mechanisms blocking genetic damage?

Muscle cells don't replicate past early childhood development, they just get bigger and add more nuclei. So muscle cancers are extremely rare compared to cancers of other tissues.

each nucleus contains a full genomic content. muscles are more of a "myosynsynctium" than a group of cells. there are cohorts of cells that are more prone to becoming cancer due to thier developmental origins and the complement of developmental mechanisms that can be reactivated.

things such as cell adhesion, and cell migration through tissue dermal cells are good at this as they do these things over the course of development.

muscles are built where they will live so these features are inhibited somewhat more completely and harder to "switch on or off"

Neat, but why don't all the cells in our body do that? What's the trade-off that goes the other way for cells most likely to get cancer (prostate, breast, lungs, lymph nodes)?

yes ! this is the nature of superoxide dismutase. basically free radicals are a price paid for generating ATP.

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

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

Is skeletal muscle cancer common? I haven't heard of it though perhaps it has another name.

rhabdomyosarcoma

Free as in radicals, not free as in beer.

As others pointed out, an increased output would not be sustainable long term within the normal body. The physiology behind action potential[1] and refractory period[2] explains how they compliment each other to make sure our system function properly and effective.

1:https://en.wikipedia.org/wiki/Action_potential

2:https://en.wikipedia.org/wiki/Refractory_period_(physiology)

Not unless having vast amounts of mitochondria is a competitive survival/reproductive advantage favoring natural selection of individuals in their environments

This resonates with my understanding: evolution is lazy, not optimal.

Or: evolution is lazily optimising. Survival doesn’t imply perfection, as it is my definition a process.

And the more optimised an organism is the more fragile it’s continued existence.

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