1. Evolution often defies survival logic.
2. Peacocks grow massive tails that hinder escape.
3. Elks develop antlers so large they can barely move.
4. Bullfrogs croak excessively, wasting precious energy.
5. Exaggerated traits persist because they signal desirability.
6. So, such traits, along with the preference for them, are passed on.
7. The biologist Ronald Fisher called this process 'Fisherian Runaway.'
8. It allows traits that set individuals apart as desirable to dominate over time.
9. Fisherian Runaway explains arms races in status, taste, fashion and even survival.
10. The value of these traits isn't inherent—it lies in how well they signal competence.
11. From exaggerated physical traits (peacock's tail) to behavioural displays (bullfrog's croak).
12. From genetic correlations (finches' beak colour) to mate choice (human facial symmetry).
13. From multiple ornaments (elk's antlers and calls) to indicator traits (birds' bright plumage).
14. Rory Sutherland recognises that many of our choices are Fisherian Runaway in disguise.
15. The choice to attend college is often less about learning and more about signalling status.
16. The choice to inflate startup valuations puts joining the 'unicorn' club over sustainability.
17. The choice to chase virtue-signalling campaigns puts awards over effectiveness in adland.
18. The choice to curate social media lives, filters and follower counts mirrors a peacock's tail.
19. Sutherland describes the 'sourdough effect' as another form of cultural Fisherian Runaway.
20. This typically occurs when one trend overshadows all others, dominating the ecosystem.
21. Sourdough bread, for instance, symbolises fine quality and thrives on its own popularity.
22. Options like rye fade—not because they're inferior, but because they're less fashionable.
23. Once a trait signals desirability, it often spirals into excess and becomes self-reinforcing.
24. The paradox is that exaggerated traits often reduce efficiency and long-term survival.
25. Evolution is not about survival of the fittest, strongest, smartest, sensible or the practical.
26. Instead, it favours traits that make the loudest, flashiest or most extravagant impression.
27. That is, the real reasons behind choices often seem counterproductive yet remain compelling.
28. Or as J.P. Morgan put it, everyone has two reasons for their actions: a good reason and the real reason.