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Name: Kiyushi
Status: student
Grade: 6-8
Location: NH
Country: N/A
Date: 6/22/2005

Why do male mammals (such as human males)gain muscle mass when they begin to "develop"? I know that the hormone testosterone causes this phenomenon, but I want to know WHY this happens. Is it an evolutionary thing, or just a mistake of nature? Thanks.

I agree, Kiyushi, testosterone is not a reason for muscle bulk, it's merely the signal-relaying substance that nature happened to start using, to dial up muscles (and other things) when needed.

It's not always the males that are bigger, stronger. In some species it's the females that are the defenders, hunters, and/or competitors for reproduction or territory. Then evolution would make them the bulkier ones. But in mammals usually it's the males. Are there any exceptions? perhaps among whales?

I have lots of fuzzy ideas that when reproductive rate is slow, and the young of the species require extended care, and the male-to-female birth ratio is about 1:1, (all for evolutionary reasons of their own), then the male tends to draw guard duty and becomes the stronger sex. For nurturing young, muscles aren't too helpful. (Counter to that, if directly defending them, muscles do help.) Muscle bulk does have a cost: it requires extra food intake just to survive. Conversely, mothers with less size may survive more often in times of scarce food, a strong evolutionary advantage.

But all this is just one family-group adaptation that is available to an evolving species. Other specialization strategies happen often enough, depending on a mess of factors.

Mistakes of nature are merely evolutionary adaptations to environments which "recently" ceased to exist. "Recently" with respect to the presently available speed of evolution. One might think that with the recent sprouting of civilization based on technology and social rules, big muscles are pointless. But I'm not so sure. Even now you can't really be sure that big muscles are not an evolutionary advantage to a given male human being. As we step thru successive revolutions: agricultural, industrial, informational, evolutionary advantages may change substantially each time. All three of these social phases exist in the world today. Things haven't changed much at all for the other (wild) mammals, except for their loss of habitat to humans. We'll see how that plays out.

As for the timing: "when they begin to develop": You can imagine that while a new member of the species is dependent, then less bulk, requiring less food, is an advantage. At some point there is a transition to adult activities, and for this part of life it seems that muscles have been an advantage for the male, at least until recently.

It's tough to think thru all the possible dependencies thoroughly enough to believe it's "science". But sometimes computer simulations can codify a largish set of one's theorized dependencies, and act them out much as evolution would, and give a quantitative result, such as a "final" population count. Then you can begin to feel less philosophical and more scientific about it. Sometimes, comparing different simulations, some factors show up as clearly more influential than others in the present situation.

Of course, sometimes evolution seems to make nature itself look like one big mistake. But it's a richly detailed mistake, with many tools at our disposal, so we may as well try to make something of it.


Jim Swenson

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