A
NS V SS
NATRL SELECTN V SXL SELECTN
It took biologists another three-quarters of a century to
apply the same principle to sexual selection for fitness
indicators. As we saw earlier, in 1975 Israeli biologist Amotz
Zahavi argued that many animal signals—including sexual
ornaments—evolved as advertisements of the animal's fitness.
He suggested that the only reliable way to advertise one's
true fitness is to produce a signal that costs a lot of fitness. This
explains why sexual ornaments are so often large, extravagant,
costly, and complicated. The peacock's tail is not just a cheap,
transient advertisement visible only to peahens. It is heavy,
encumbering, hard to grow, hard to preen, and highly visible
to predators. Peacocks have to drag it around everywhere they
go. Unfit peacocks might be able to grow large tails, but they
would not be strong enough to carry them while finding food,
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Here's a clear and focused comparison between Natural Selection and Sexual Selection, especially in the context of Geoffrey Miller’s The Mating Mind:
🧬 NATURAL SELECTION vs SEXUAL SELECTION
| Aspect | Natural Selection | Sexual Selection |
|---|---|---|
| Definition | Traits that help an organism survive and pass on genes | Traits that help an organism attract mates and reproduce |
| Key Driver | Environmental pressures (e.g. predators, climate, food scarcity) | Mate preferences and competition for mates |
| Traits Selected For | Practical traits: strength, camouflage, disease resistance, efficiency | Flashy, ornamental, or expressive traits: beauty, intelligence, creativity, humor |
| Examples in Nature | Giraffe's neck (to reach leaves), thick fur (for cold), immune system strength | Peacock’s tail, bird songs, antlers, elaborate mating dances |
| Human Example (Miller) | Basic problem-solving, tool use, walking upright | Language, art, music, humor, generosity, storytelling |
| Cost of Traits | Typically efficient and low-cost | Often costly or extravagant, showing fitness by “wasting” energy/resources |
| Ultimate Goal | Survive long enough to reproduce | Attract the best mate, increasing chances of gene success |
| Timescale | Operates over long periods, shaping adaptation to environment | Can drive rapid change, especially when mate preferences shift |
🧠 In The Mating Mind…
“Natural selection made us smart enough to survive; sexual selection made us smart enough to be interesting.”
Miller's Main Argument:
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Natural selection alone cannot explain the rapid development of the human brain and mind.
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Sexual selection—particularly mate choice—favored mental traits that are hard to fake and easy to judge, such as:
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Creativity
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Storytelling
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Moral character
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Artistic skill
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These are mental ornaments—like a peacock’s tail—that evolved not for survival, but for display during courtship.
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Here’s a simple explanation of the three main theories of sexual selection:
1. Runaway Theory
“Attraction gets out of control.”
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A trait becomes attractive (like a long tail).
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Mates prefer it, so it gets passed on.
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Over time, both the trait and the preference for it keep growing.
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Example: Peacocks’ tails.
2. Indicator Theory
“The trait shows good genes.”
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A trait signals health, strength, or genetic quality.
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It's costly or hard to fake, so only the best individuals can afford it.
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Example: Bright feathers = healthy immune system.
3. Sensory Bias Theory
“It tricks the senses.”
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Some traits become attractive just because they match something the brain already likes.
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Example: A red patch on a bird may attract females because they already notice red fruits.
Let me know if you'd like visuals or analogies to help remember them!
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