Part II: "The Runaway Process"

Let's assume ancestral people started out plain-looking. Then through some minor genetic-shift, females developed a hankering for say, males with large heads. If this big-headed phenomenon happened to occur in bigger, better males, then females who chose them would probably produce more, and healthier offspring. Big-headed genes would proliferate in males, and the preference for them in females. This is all well and good, but sooner or later, conventional knowledge is that females soon come to focus single-mindedly on this trait, regardless of it's correlation with the overall quality of the male anymore.
Thus begins the cycle of runaway one-upmanship: over hundreds and thousands of generations the human head continues to get larger until no self-respecting male can get a date unless he's got that mega-dome. Natural selection steps back in to stop this nonsensical runaway process at the point when the quest for better sexual ornamentation is slowing the males down enough and attracting enough predators to kill them. To a degree, we have lost much of this natural system of checks-and-balances in the modern human world, so the nonsensical runaway system has free reign over the dominion of female sexual preference. This is where everything starts to turn terrible in human world.
In the natural world where the balancing factors are more available, the system proceeds in an orderly fashion. The arctic fox with the "Eat Me" sign wouldn't make it through a single winter with that bullseye on him unless he was very good at out outrunning polar bears. It is this underlying, and necessary consequence of his bold, and risky male behavior that the females reproductive system is attracting her to, often unbeknownst to her.

Why girls like the "bad boy" Pt. I

Excerpts from The Natural History of The Rich - R. Coniff

It's really relegated to nothing more than a vestige of ancestry in the modern human world, but in the natural world, there is a very clear cut answer to this puzzling question. Natural selection basically means that nature weeds out unfavorable traits by killing individuals that display them. Thus an arctic fox with a patch of red fur spelling the words "Eat Me" on it's his side would quickly end up in a polar bear's belly regardless of the bear's illiteracy. Whereas those with more favorable traits like plain white fur for camouflage in the snow will be more likely to survive and reproduce.
In most species, the females control the mating and most of the sexual selection, and they often have an irresistible attraction to the male with the "Eat Me" sign. That is, they seem to select males for traits that make them less likely to survive.
In peacocks for example, the upkeep on a big flashy tail requires the male to waste huge amounts of energy. It also inhibits his ability to fly and makes him more vulnerable to predators. The female's own drab coloration attests to her abiding faith in the value of camouflage, yet she will nontheless choose a male with a bigger showier tail almost every time.
To be fair it works both ways, for example small breasts are just as good as big ones for nursing babies, and in our ancestral environment flat-chested females would also have been better equipped for climbing trees and running from predators. But men like larger breasts, having them is of course a handicap, a cost ancestral women undertook to display greater nutritional fitness in the form of visible body fat in a desirable location.
Given the ruthless efficiency of the natural world, how could such costly displays have evolved in the first place?