Natural selection that consistently favors individuals at one extreme of a trait distribution, causing the population mean to shift in that direction over time. It reduces genetic variation for the selected trait.
From Latin 'directio' meaning 'a straight line or course' and 'selectio' meaning 'choice'. The term was formalized in the 1930s as evolutionary biologists developed mathematical models to describe different patterns of natural selection.
Directional selection is like evolution with a clear goal - bigger, faster, stronger, or smarter! The classic example is how horses evolved from tiny dog-sized creatures to today's large animals as grasslands expanded and longer legs became advantageous for escaping predators.
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