Natural Selection, explained.
Natural selection changes inherited variant frequencies through differences in expected survival or reproduction in a particular environment.
Why it happens
A haploid frequency p updates to pwA/(pwA+(1−p)wB). Relative fitness is 1.2 versus 1; reversing the environment swaps those values. Generation buttons update the deterministic recurrence while preserving history.
Natural selection changes inherited variant frequencies through differences in expected survival or reproduction in a particular environment.
Read the result
Frequency responds to relative fitness, not a preference for progress. Reverse the environment while retaining history to see an advantage change sign.
A worked example
A variant in two environments
Begin with A at fifty percent and give it relative fitness 1.2 while the alternative has fitness one.
Advance ten generations and observe the deterministic increase, then reverse the environmental advantage without resetting frequency.
Advance again. The direction changes because reproductive contributions changed, not because variants anticipated the new environment.
OPTIONAL DEEPER DETAILGo deeper: inside the model
Inside this model
A haploid frequency p updates to pwA/(pwA+(1−p)wB). Relative fitness is 1.2 versus 1; reversing the environment swaps those values. Generation buttons update the deterministic recurrence while preserving history.
Where this idea is useful
A practical use
A resistance variant can become more common under a particular environmental pressure without organisms choosing to acquire it.
A common misconception
“Selection gives organisms the traits they need.”
This model changes frequencies of existing inherited alternatives through differential reproduction. It contains no foresight, need-driven mutation or goal.
What this explanation leaves out
- This one-locus model omits mutation, drift, migration, inheritance complexity and changing population size. Fitness means relative reproductive contribution here; it is not moral worth or a universal measure of organism quality.
Why does a rare variant not vanish immediately?
The recurrence changes expected proportions continuously. Without sampling or an explicit extinction rule, a positive frequency can remain positive while becoming very small.
Which environmental condition makes a trait advantageous rather than advantageous everywhere?
Associated thinkers
Associations marked provisional are awaiting source review.
Further reading
Explore the original research or the teaching reference behind this experiment.