Weapon costliness keeps signals honest by excluding weaker males

Evidence

For animal weapons to be honest signals, they must be expensive—exorbitantly expensive. So expensive, in fact, that only the top-condition males can afford them. Costs keep signals honest. If anybody could afford big weapons, then all males would have them, and differences in weapon size would be meaningless. Only when most males cannot possibly afford them will big weapons provide reliable signals of fighting strength. Then, and only then, will it pay for males with small weapons to walk away. — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 601 (#corroborates, 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 (#complicates, via linked claim)

To use the same basic equation I allude to in the text, the benefits of having big weapons (B), representing the offspring produced by the females they guard, are offset by production, maintenance, and fighting costs (C). When B − C > 0, then selection drives the evolution of weapons toward ever greater size. What’s not shown is our assumption that males are gleaning 100 percent of the fertilizations of the females they defend: (1 * B) − C > 0. Cheating males erode the rewards to dominant males, so that they reap only a fraction of the sired offspring that they otherwise would have. In the hypothetical beetle example where sneak males, on average, steal one-fourth of the fertilizations, the new equation would be: (0.75 * B) − C > 0. Benefits are devalued by the proportion of fertilizations stolen by cheaters (1 − 0.25 = 0.75). At some point, if cheaters steal enough, the realized benefits may be low enough that they no longer exceed the costs, even for the most successful guarding males. — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 851 (#complicates, via linked claim)

Categorization

• XREF: connects to: Weapon expense is what keeps signals of fighting ability honest — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 601; Weapons are better signals than body size because they vary from zero to enormous — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 353; Sexual weapons sometimes protect rather than burden their bearers from predators — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 774 (+11 more)

Related

• Cheating males erode the reproductive payoff of weapons, capping their evolution (similarity 0.92)
• Successful cheaters can reverse selection so big weapons collapse (similarity 0.92)
• Weapon expense is what keeps signals of fighting ability honest (similarity 0.92)
• Extreme skew in mating success drives arms-race escalation in weaponry (similarity 0.91)
• Bigger weapons usually fail because their costs outweigh their benefits (similarity 0.90)
• Weapon escalation ends when costs outweigh benefits and cheaters invade (similarity 0.90)
• Sexual selection drives weapons to extremes because payoffs for winners are enormous. (similarity 0.89)
• Poor-quality males pay steeper costs for large weapons and so invest less (similarity 0.89)
• Weapon size in animal species is under stabilizing selection, not open-ended directional selection (similarity 0.89)
• Only a minority of males can afford to build full-size weapons (similarity 0.89)
• Weapons evolved as signals so males could predict fight outcomes before risking battle (similarity 0.88)
• Natural selection usually favors modest weapon size because cost offsets benefit (similarity 0.88)
• Deterrence amplifies the evolutionary payoff of extreme weapon size. (similarity 0.88)
• Weapons primarily deter rivals rather than inflict harm in actual fights (similarity 0.88)
• Balanced selection keeps most animal weapons modest rather than extreme. (similarity 0.88)

Broader Connections

• Weapon expense is what keeps signals of fighting ability honest #corroborates (0.95) — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 601
• Natural selection usually favors modest weapon size because cost offsets benefit #complicates (0.60) — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 21
• Cheating males erode the reproductive payoff of weapons, capping their evolution #complicates (0.55) — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 851
• Weapons are better signals than body size because they vary from zero to enormous #expands (0.50) — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 353
• Weapons primarily deter rivals rather than inflict harm in actual fights #expands (0.50)
• Weapons work primarily as deterrents that prevent fights rather than win them #expands (0.50) — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 966
• Extreme skew in mating success drives arms-race escalation in weaponry #expands (0.50)
• Weapon escalation ends when costs outweigh benefits and cheaters invade #expands (0.45) — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 457
• Males that assess rivals before fighting survive and reproduce better. #expands (0.45) — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 380
• Sexual weapons sometimes protect rather than burden their bearers from predators #complicates (0.40) — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 774
• Extreme weapon size faces stabilizing, not open-ended, selection in real populations #complicates (0.40)
• Deterrence amplifies the evolutionary payoff of extreme weapon size. #expands (0.40) — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 387