That’s probably generally true across many species, but it’s not necessarily true for every one.
For instance, maybe there really is no significant survival drawback to getting bigger (at least at the current typical sizes), and every male is just getting as big as his resources allow him to be. Or, kind of similarly, possibly the larger males are at the optimum survival size; it’s just that the smaller ones aren’t getting to that size because of parasites or other problems.
That’s an important point too - evolution has to be moderately slow to allow everything to catch up. There are people well over 6’0" but the rest of the body has to evolve to handle that- Kobe Bryant, for example, had to quit because his knees couldn’t take it. Our skeletons are scaled for 5’10" not 7’0". Double the size of a person, the area of their knee joint increases by 4x, but their weight increases by 8x. So even a 20% increase in scale can be long-term detrimental.
Similarly, we’ve bred elegant thin domesticated horses from the small ponies originally found wandering the plains of east Europe/Asia. their bones did not scale proportionately (except maybe Clydesdales) so breaking a leg is always a risk.
What happens with natural evolution is that the pieces scale as demanded, through the basic process of “not good enough, you die early”. humans short-circuit this process, by limiting for example, the need for horses to run frequently from predators, by selecting for breeding based on appearance not suitability to avoid fractures (except in extreme cases). Between crutches and laws prohibiting big guys from raping the girlfriends of small guys, there is less evolutionary selection for healthy and larger humans. (and absent armies of eunuchs to guard the harem or the isolation of a Great Salt Lake, most societies don’t have highly polygamous marriage arrangements for the males in general.)
For mother nature, we have examples like elephants, where the bones are appropriately scaled; but again, speed and endurance are limited compared to a cheetah or deer. Except for elephants in the tropics where food is abundant much of the year, there appears to be a size limit on grazers -and note the bigger ones, like cows, oxen, etc. seem to be fighters, not runners - there’s a limit factor to size and speed. (and which defence is dictated by the type of predator).
Perhaps the closest to what the OP suggests would be some seals, where the bull can significantly outweigh the typical cow by a huge amount. Again, there is less demand that the skeleton support a different weight is less of an issue in water, and as for food, your mother will happily tell you there are plenty of fish in the sea. The seal cubs do not have to be as agile-mobile as newborn deer or antelope, so can be born fairly small and grow. Seals tend to beach in areas isolated from land predators, giving the cubs time to grow and get mobile.
A metaphor: A young bull and an old bull are roaming the range. From a hilltop, they look down at a pen filled with cows. The young bull says, “Look at those beauties! Let’s run down there, jump the fence, and fuck a cow!” The wise old bull says, “No, sonny. Let’s amble on down, nudge the gate open, talk a bit, and then fuck them ALL!”
There’s more to successful breeding than mere aggression. Besides the “sneaky fuckers” mentioned upthread, cooperative species seem to at least as well (at the species level) as competitive species. See Cooperation, Conflict, and the Evolution of Complex Animal Societies. As for size, consider a big, strapping fellow with a rare, luscious fifteen-inch schlong. How many human women could accommodate that monster and pass along the supersize genes? Seems like an evolutionary dead-end.
Note: I’m 6’4" tall with size 18 feet. Dad was 6’1" with size 13’s. His father was smaller. My son should thus stand 6’8" and wear size 24! Too bad he doesn’t exist; basketball (or foot chinko) lost a star.
There is no single simply inherited genetic trait for tallness. That means that it is not possible to just increase in height rapidly until you run into the next limit. Thee is a great deal of randomness in height, and tall parents have shorter kids.
You can see that this has not been the most important factor in humans, because populations have just increased in height immediately, in just the last two generations, when kids got more and better food and weren’t as sick.
The daughter from my first wife, at 5’10", is midway between her parents’ heights. But her nose is as long as mine. I’m glad she didn’t have it shortened. Nephews and nieces from my siblings and their tall mates are themselves taller than the national average, but mostly below my 99th percentile ranking.
I’ll blame much recent increase on growth hormones in McFoods as well as generally improved healthcare and nutrition. I doubt many of us were stretched on torturers’ racks or spent time dangling by our ankles.
The phrase “survival of the fittest” is an erroneous description of the mechanism of natural selection. The actual process is procreation by the survivors. Big has advantages and costs, those factors are not constant over time. Every now and then, situations will arrive that make the cost of big have more negative consequences. If those factors last over species lifetimes, the gene pool will conserve more of the smaller members genes. Then the larger among that smaller average may again have mating advantages. From the point of view of evolution, why you don’t survive is only important while it remains significant over multiple generations.
You’re assuming that the animals who come back to mate are larger than their parents were and/or are larger on average than average within their peer age group.
Assume that the average size is X. A new generation is born who are all plus or minus of X by up to 10%. They go out into the world, hunt, bathe, drink beer, join a chess club, etc. and eventually come back to breed.
During the time that they were out being wreckless and learning to hunt, all the ones larger than X have perished. They were too big and clumsy.
So all the midgets and average X sized ones get back to meet the opposite gender. They duke it out and all the midgets are obliterated.
The average size of the parents of the next generation are all almost exactly X in size. They were the largest of all those in the giant battle for booty, but are no larger than their parents.
If they had been larger then the species would, indeed, quickly grow in size. That the species doesn’t grow is evidence that the “largest” were just average. The Andre the Giants of the bunch fared the same as Andre the Giant.
Yep, kleptogyny is definitely going to re-balance things.
Also, a predator that preferentially takes the biggest and strongest rather than the sickest and weakest would also have a negative effect…
The fact you wrote “luscious” and “fifteen-inch schlong” in the same sentence would make it obvious you’re a man because I don’t know any woman who really thinks a dick that big is desirable. I am becoming more and more of a fan of the notion that the size of the human penis evolved as a display towards other men because it’s the men who universally think bigger is better, not women.
Likewise, the size of elephant seals or the racks of deer and moose might not have evolved because the females like them but to fight off other males and the females just put up with the guys’ obsessions about blubber or antler size.
Would any woman even want to try?
Guys, really, giant dicks of that sort are not appealing. A lot of women are going to see that and they won’t think “sexy” they’ll think “ouch”.
You have to wonder if in other species there’s a point where the females go uh… not so much, please.
Also, successful human reproduction, particularly pre-civilization, often depended on the man not only being well hung but also helping to raise the offspring. If his magnificent penis is so large he keeps tripping over it while pursuing game not only will the lesser endowed males laugh at him, his mate and kids might starve for lack of adequate food/protein.
Sorry I omitted the “snark” emojis.
Larry Niven in an article a while ago complained about unrealistic fanfiction (???) on his feline Kzinti aliens. Like much fan fiction it delved into the sexual. Niven pointed out how unrealistic it was - that animals where males hunted and fought and kept harems would not have large equipment - It was too vulnerable in fights with prey or other males. Horses are known for the size of their “equipment” but it needs to be long for a practical purpose, just to reach. In situations like that, another blow to extremely large males, so to speak, is the risk of crushing/injuring the female. (There’s the story of how that is a risk with elephants if the male takes too long…)
Desmond Morris had a book (or perhaps it was an excerpted series of chapters) about “why is Sex Fun?” discussing assorted mating strategies. Short answer, recreational sex keeps the man around to feed his offspring. Similarly women have hidden fertility, to also keep the man around because he cannot guarantee he’s accomplished his task for a while. There are plenty of other strategies. Without bonding, some monkey tribes simply have unlimited promiscuity - but the females signal fertility so they only need to perform when they are really fertile. This is another issue - mating takes time and effort, so is wasted when it does not result in reproduction, unless there is a different benefit.
As for regression to the mean - this is not what evolution is about. If size is selected for - then every so often, there may be a genetic mutation that results in bigger growth. It may or may not be tied to the Y chromosome. (And note that in evolutionary time, by transcription errors, such genes can move around.) If it’s advantageous to have the “bigger” gene, and if it’s more advantageous fo it to be tied to the Y chromosome, then that will begin to dominate the species. Over millennia, if there’s an advantage, then bigger will dominate.
But note the importance of environment. There are grazers who are in marginal environments - goats, deer, etc - and animals who have to run fast - antelope, deer - these tend to be not much bigger than a large dog. There are animals - cows, water buffalo, musk ox, wildebeest - that put their horns down and fight prey. They are bigger, and tend to inhabit areas where there is plenty of grazing. It’s the tradeoff again - bigger animals need huge swaths of grass to feed themselves, which they won’t find in rocky hilly terrain. Heavy animals do not run well; they can’t run if there is thick forest. Every evolutionary result is a compromise between food and evasion of prey.
This seems like a lengthy way of saying that past a certain point additional size/weight is a survival disadvantage. This has been discussed at some length in this thread.
But to the extent that you’re addressing the question at hand, it’s by oversimplification.
Since the larger size is a mating advantage, there’s a tradeoff in terms of reproductive success between survival and mating. So the equilibrium point would logically be somewhere between the two optimum sizes.
It’s extremely unlikely that genetics has zero impact on size/height or that the varying size/height is completely unrelated to variations in genetics. And as long as genetics is a factor, even if it’s not the only factor, the point holds.
The fact that genetics is not the only factor is why I brought up regression to the mean. (More below.)
You’re referring to mutation-driven changes in size. The process I’ve been referring to is based on changes in average size that draw on the already-existing genetic variation within a given species. But since the process is driven by the actual size and not the genetic predisposition for size, and since the actual size is based on a combination of genetic predisposition and other influences, regression to the mean applies.
This question reminded me of the lek paradox. I wonder if they are related.
I always thought the same and wondered what the basis for this argument might be. But you got me to thinking about it again, and now I’m thinking that it might be that it has a logic to it, based on female offspring.
Even if the males with these characteristics have a net decrease in fitness vs other animals, their female offspring would not inherit the gender-specific handicap, but would still share whatever compensating aspects that the father had, so for them it’s a pure benefit. From the perspective of the mother’s mating selection, as long as the advantage to her daughters is greater than the disadvantage to her sons, it would seem that she’s better off with that selection.
Which brings us around in circles to the basic point. Size is not the only or the deciding advantage. With human animal husbandry, we can protect animals from the worst disadvantages of selecting for a singular characteristic - animals bred for one trait to the detriment of life skills. (I.e. Pugs that can’t breathe, Dalmatians with hip problems, giant pigs too stupid to not roll over on their litter, horses with a strong tendency to break a leg…) Nature is not so forgiving. Perhaps your question answers itself. If animals become too big to the detriment of say, smarts - a common effect of inbreeding - then they are vulnerable to other dangers that are not rival males. Too stupid or confused to escape prey? Too stupid to track their females and prevent sneaky reproducers? Too likely to have a heart attack or stroke? Brittle bones or fragile knees?
As I also said - the square-cube law. an animal twice as big is eight times the weight, needs to eat and chew and process maybe 8 times the food. Does the environment support that? Will he have time to chew his food properly (which grazers need to do) and also reproduce? Inquiring minds need not know.
Food supply and surface to volume ratio, for heat loss, limit maximum survivable size.