Extreme weapon size faces stabilizing, not open-ended, selection in real populations

Evidence

Surprisingly few studies have actually measured the strength and nature of selection on extreme weapons—it’s incredibly labor-intensive to do. But those that have often find that as weapons get bigger and bigger the success of males rises up to a point, beyond which success begins to drop. Males with the very largest weapons tend to do worse than males with slightly smaller weapons. If males with the biggest weapons of all fared the best, selection would be “open-ended” and directional. The fact that the very biggest males did slightly worse shows us that selection in these populations is stabilizing, and it suggests these populations may be at or close to their balance point. — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 850 (#corroborates, via linked claim)

For as long as I can remember I’ve been obsessed with big weapons, which is rather surprising given that I descend from a long line of Quakers. On field trips to the natural history museum it wasn’t birds or zebras that caught my eye; it was mastodons with curling tusks, or triceratops with five-foot-long horns. In every room, it seemed, loomed another species with a crazy protrusion jutting from its head, or from between the shoulder blades, or from the end of its tail. Gallic moose wielded twelve-foot-wide antlers, and arsinotheres had horns six feet long and a foot wide at the base. I couldn’t peel my eyes from these creatures. Why were their weapons so big? — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 2 (#contradicts, via linked claim)

Huge animal weapons look too awkward to be favored by selection, and in the vast majority of cases, this appearance isn’t misleading. Big weapons are ungainly, and most individuals fare poorly with them. For most weapons in most species, selection favors modest size and minimal cost—enough tooth to bite or grab prey, for example, but not enough to slow you down or impair your ability to maneuver. What this actually means is that selection on weapons is balanced: bigger weapons may be better for stabbing or biting, but they are also more expensive to produce and more difficult to carry. The result is a tenuous balance, much like a game of tug-of-war, which accounts for the multitude of unimpressive weapons adorning the vast majority of animal species. — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 21 (#qualifies, via linked claim)

Categorization

• XREF: connects to: Successful cheaters can reverse selection so big weapons collapse; Weapon costliness keeps signals honest by excluding weaker males; Weapon size in animal species is under stabilizing selection, not open-ended directional selection — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 850 (+14 more)

Related

• Weapon size in animal species is under stabilizing selection, not open-ended directional selection (similarity 0.95)
• Balanced selection keeps most animal weapons modest rather than extreme. (similarity 0.94)
• Species with huge weapons often show weak current selection on them. (similarity 0.92)
• Natural selection usually favors modest weapon size because cost offsets benefit (similarity 0.92)
• Bigger weapons usually fail because their costs outweigh their benefits (similarity 0.91)
• Sexual selection drives weapons to extremes because payoffs for winners are enormous. (similarity 0.90)
• Reproductive success, not survival, drives the largest animal weapons (similarity 0.90)
• Balancing selection normally curbs weapon size until some lineages escape into runaway arms races (similarity 0.90)
• Sexual selection can be far stronger than natural selection and drives weapon extremes (similarity 0.90)
• When balancing selection fails, bigger weapons win every round and escalate the race. (similarity 0.90)
• Each weapon-size increase resets the competitive baseline, ratcheting populations upward (similarity 0.89)
• Predator weapons stay small because larger ones hinder hunting (similarity 0.89)
• Animal weapons evolved to extremes far beyond practical size (similarity 0.88)
• Weapon costliness keeps signals honest by excluding weaker males (similarity 0.88)
• Deterrence amplifies the evolutionary payoff of extreme weapon size. (similarity 0.87)

Broader Connections

• Weapon size in animal species is under stabilizing selection, not open-ended directional selection #corroborates (0.95) — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 850
• Natural selection usually favors modest weapon size because cost offsets benefit #qualifies (0.70) — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 21
• Animal weapons evolved to extremes far beyond practical size #contradicts (0.70) — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 2
• Competition for reproduction drives evolution of nature’s biggest weapons #contradicts (0.65) — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 136
• Deterrence amplifies the evolutionary payoff of extreme weapon size. #complicates (0.60) — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 387
• Sexual selection can be far stronger than natural selection and drives weapon extremes #contradicts (0.60) — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 177
• Balancing selection normally curbs weapon size until some lineages escape into runaway arms races #qualifies (0.60) — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 22