Balancing selection normally curbs weapon size until some lineages escape into runaway arms races

Evidence

Yet, every so often this balance is tipped. Here and there, sprinkled across the tree of life, are animal lineages where modesty of proportion was cast aside. The evolution of weapons in these species surged forward unencumbered. Gone were the shackles of balancing selection, and all that remained was selection favoring bigger and bigger weapon sizes. Here, individuals with the most grotesque or extreme armaments beat opponents with smaller weapons. In so doing, they secured opportunities to breed. Their progeny, as impressive in their weapons as their parents, quickly replaced earlier forms and advanced the population another notch in weapon size. As soon as the next new innovation arose—an even larger or more complex variant of the existing design—the process repeated itself. Again and again, individuals with the newest and biggest weapons won, replacing those with earlier and smaller forms, and this process pushed the population still further on the path to extreme. In short, the weapons of these species got caught up in an arms race. — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 22

Categorization

• XREF: connects to: Extreme skew in mating success drives arms-race escalation in weaponry; Arms races inevitably stall as weapon costs neutralize reproductive benefits — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 432; Successful cheaters can reverse selection so big weapons collapse (+22 more)

Related

• When balancing selection fails, bigger weapons win every round and escalate the race. (similarity 0.93)
• Balanced selection keeps most animal weapons modest rather than extreme. (similarity 0.92)
• Each escalation in weapon size resets the competitive baseline and triggers the next round (similarity 0.92)
• Arms races inevitably stall as weapon costs neutralize reproductive benefits (similarity 0.92)
• Extreme skew in mating success drives arms-race escalation in weaponry (similarity 0.91)
• Weapon size in animal species is under stabilizing selection, not open-ended directional selection (similarity 0.91)
• Each weapon-size increase resets the competitive baseline, ratcheting populations upward (similarity 0.90)
• Species with huge weapons often show weak current selection on them. (similarity 0.90)
• Natural selection usually favors modest weapon size because cost offsets benefit (similarity 0.90)
• Extreme weapon size faces stabilizing, not open-ended, selection in real populations (similarity 0.90)
• Sexual selection drives weapons to extremes because payoffs for winners are enormous. (similarity 0.89)
• Dueling plus competition and defensibility is the general rule for extreme weapons (similarity 0.88)
• Specific conditions are required before weapons escalate into an arms race (similarity 0.88)
• Sexual selection can be far stronger than natural selection and drives weapon extremes (similarity 0.88)
• Successful cheaters can reverse selection so big weapons collapse (similarity 0.88)

Broader Connections

• Weapon size in animal species is under stabilizing selection, not open-ended directional selection #corroborates (0.75) — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 850
• Releasing soldiers from other tasks lets weapons evolve to extremes #expands (0.70) — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 128
• Specific ecological circumstances must align before weapon arms races begin #qualifies (0.70) — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 137
• Each weapon-size increase resets the competitive baseline, ratcheting populations upward #expands (0.65) — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 183