Advantageous Traits Spread
Aligned to HS-LS4-3 — Next Generation Science Standards.
What this lesson teaches
When a trait improves survival or reproduction, the individuals carrying it leave more offspring. Over generations, that trait's proportion in the population rises in a way that can be measured.
Worked examples
Example 1
In a moth population, dark moths hidden on soot-darkened tree bark survive birds better; within decades their share climbs from a few percent to the majority.
Example 2
When the soot was cleaned up, the light moths came back. The environment, not the moth, decided which colour was an advantage.
Example 3
A trait spreading says nothing about it being good in general. It was good there, then.
Practice questions
- From two data sets, describe how a trait's frequency changed over time.
- Calculate the expected proportion of a trait if it doubles each generation for three generations.
- Use probability to support the claim that advantageous traits become more common over time.
Watch the lesson
Every lesson comes with a video taught in English and Spanish — the same video the QR code in the printed workbook opens.
▶ Watch this lessonEn español
Los rasgos ventajosos se propagan
Cuando un rasgo mejora la supervivencia o la reproducción, los individuos que lo portan dejan más descendencia. A lo largo de las generaciones, la proporción de ese rasgo en la población aumenta de una manera que puede medirse.
Ejemplo 1: En una población de polillas, las polillas oscuras camufladas en la corteza ennegrecida por el hollín sobreviven mejor a las aves; en pocas décadas su proporción sube de unos pocos por ciento a la mayoría.
Ejemplo 2: Cuando se limpió el hollín, las polillas claras regresaron. El ambiente, no la polilla, decidió qué color era una ventaja.
Ejemplo 3: Que un rasgo se extienda no dice nada sobre que sea bueno en general. Fue bueno ahí, entonces.
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