Selection doesn't need any type to die out
- The idea
- Predict
- See it
- Why
- Check
The idea
“If every type is still surviving and breeding, selection isn't happening.”
Selection usually gets shown as a die-off, where the slow ones get eaten. Often it's quieter, a small edge in offspring repeated every generation.
The short version
The mistake: If every type is still surviving and breeding, selection isn't happening.
What's actually true: Any steady, heritable difference in survival or reproduction is selection, even when every type keeps breeding.
- Natural selection happens whenever heritable variants differ, on average, in how many surviving offspring they leave.
- That average is called fitness, and only fitness compared with the other types matters. A 2% edge is still an edge.
- The edge compounds. Each generation the favored type makes up a little more of the parents, so its share keeps climbing.
- Heavy losses alone don't cause selection. If deaths hit every type at the same rate, the shares are expected to stay put.
On the exam: Compare offspring per individual. If one type leaves more on average, its share rises.