When the exposure happens can matter more than how long
- The idea
- Predict
- See it
- Why
- Check
The idea
“The longer exposure should cause the bigger effect, whenever it happened.”
More of a cause usually means more of the effect, so adding up total exposure feels safe. Each trait is built at its own stage of development, though.
The short version
The mistake: The longer exposure should cause the bigger effect, whenever it happened.
What's actually true: Many environmental effects act only during a sensitive window of development, so timing can outweigh total exposure.
- Many environmental effects on phenotype act only during a sensitive period, the stage of development when that trait is being built.
- The same exposure before or after that window does little to the trait. So more total exposure doesn't always mean a bigger effect.
- Experiments find the window by shifting the condition at different stages.
On the exam: Ask when the trait is built. Outside that window, even long exposure can do little.