Question

Red-eyed tree frog eggs can hatch up to two days earlier than average if they experience vibrations in their environment. If they hatch more than two days earlier, the embryos are not developed enough to survive outside of the egg. Explain how natural selection keeps frog eggs from hatching earlier than two days before expected hatching?

Answer 1

Natural selection keeps eggs from hatching more than two days early because embryos that do so don’t survive to reproduce, so the variants that cause extreme early hatching are removed from the population.

Stepwise explanation:
- There is heritable variation among embryos in how readily they respond to vibration cues (different sensitivity thresholds or timing of developmental readiness).
- Vibrations sometimes signal a real threat (e.g., a predator) and early hatching up to ~2 days can increase survival in those cases.
- If an embryo hatches >2 days early, it is developmentally too immature and dies, so it leaves no offspring carrying the genes for that overly-early response.
- Over generations, alleles/traits that cause excessive sensitivity and >2‑day early hatching are selected against and decline in frequency. Alleles that produce the “safe” threshold — respond to true danger but not to cues that would trigger lethal premature hatching — are favored.
- The result is an evolved reaction norm (a tuned threshold and developmental timing) that balances escaping predators with the need for sufficient maturation inside the egg. This is essentially stabilizing selection on hatching timing.

In short: embryos that hatch too early die and cannot pass on the tendency, so natural selection filters those tendencies out and preserves a hatching response that rarely exceeds the survivable two‑day window.