--- title: "Sexual Selection, Mate Choice and Parental Investment" description: "When one sex invests more per offspring, that sex becomes the limiting resource and the other competes for access. Traits that lower survival can still spread if they raise mating success by more than" canonical: https://lightmysky.com/learn/science/sexual-selection-mate-choice-and-parental-investment-mt_6oTPGFw_p5 source: https://lightmysky.com/learn/science/sexual-selection-mate-choice-and-parental-investment-mt_6oTPGFw_p5.md retrieved: 2026-09-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Sexual Selection, Mate Choice and Parental Investment When one sex invests more per offspring, that sex becomes the limiting resource and the other competes for access. Traits that lower survival can still spread if they raise mating success by more than they cost. Subject: Science · Area: Ecology & Conservation · Ages 20 to 21 Page: https://lightmysky.com/learn/science/sexual-selection-mate-choice-and-parental-investment-mt_6oTPGFw_p5 ## Ready when they can - Predicts which sex competes and which chooses from the investment each makes. - Explains how a costly ornament can be favoured despite lowering survival. - Uses a case where roles are reversed to test the argument rather than to break it. ## Lesson: Why the showy sex shows off Behavior has two kinds of causes. Proximate causes sit in nerves and hormones, while ultimate causes sit in fitness payoffs. Sexual selection is selection through mating success rather than survival alone. The sex that invests more per offspring, usually females, becomes choosy, while the lower investing sex, usually males, competes for access. **Example.** A long tail or loud song that slightly raises predation risk can still spread if choosy mates reward it strongly. The ornament is then an honest signal, since only vigorous individuals can afford to carry it and survive. Where males carry the eggs or do most of the feeding, the roles flip: males turn choosy and females compete to impress them. Every display carries an opportunity cost under a limited lifetime budget. Energy spent on one more mating display cannot also feed chicks or fund future broods. Contests within one sex for mates differ from mate choice by the other sex: the first is rivalry, the second is selection by preference. Guarding or feeding young pays only when the extra survivors outweigh the future broods sacrificed. **Tip.** The rule is about investment, not about maleness itself. High investment per offspring favors choosiness, because each breeding decision carries a large cost. When you meet a seeming exception, check who invests more: the exceptions test the rule rather than breaking it. **Recap.** The higher investing sex chooses while the lower investing sex competes, so costly ornaments spread when mating gains outweigh survival costs. ## Practice 8 questions on this page, each with its working shown. ## Needs first - [Selection Coefficients and Predicting Allele Frequency Change](https://lightmysky.com/learn/science/selection-coefficients-and-predicting-allele-frequency-change-mt__JS2XJxOXV) - [Optimal Foraging and the Currency of a Behavioural Decision](https://lightmysky.com/learn/science/optimal-foraging-and-the-currency-of-a-behavioural-decision-mt_9iNYB7d1Rh) ## Opens up - [Kin Selection, Relatedness and When Helping Pays](https://lightmysky.com/learn/science/kin-selection-relatedness-and-when-helping-pays-mt_scVf8G34WI)