Natural selection needs variation, inheritance, and differential survival
Evolution by natural selection occurs when traits vary, are inherited, and affect reproductive success.
Takeaway
Selection is not a plan; it is a filter acting on existing variation.
What I learned
Natural selection requires three ingredients: variation among individuals, inheritance of some traits, and differences in survival or reproduction connected to those traits.
Why it matters
This helps avoid thinking of evolution as intentional progress. Selection works with what already exists and changes populations over generations.
A useful framing
Ask what varies, what is inherited, and what changes the odds of leaving descendants.