Selection favouring one extreme phenotype, shifting the population mean in one direction.
The mean of a trait moves toward one extreme, as in antibiotic resistance, body size in warming climates and beak size in finches. It reduces variation if continued.
Graphically, the bell curve shifts.
Selection favouring one extreme phenotype, shifting the population mean in one direction.
Directional Selection is one of the 53 topics in Evolution. It is rated Intermediate, so it suits learners who already know the core vocabulary. Related topics in this area include Stabilising Selection, Sympatric Speciation, Disruptive Selection.
Elephants in poaching areas are increasingly born without tusks because tusked animals are killed.
Work through the Beginner topics in Evolution first, such as Evolution, Natural Selection, Charles Darwin, then return to Directional Selection. Intermediate topics assume the Beginner vocabulary.
The closest topics to Directional Selection are Stabilising Selection, Sympatric Speciation, Disruptive Selection, Allopatric Speciation. Comparing them side by side is a good way to see how the ideas connect.
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Directional Selection. To practise the whole of Evolution, use the Evolution quiz.
Directional Selection: Selection favouring one extreme phenotype, shifting the population mean in one direction. Stabilising Selection: Selection favouring intermediate phenotypes, as seen in human birth weight. Read both side by side and note what each one explains.
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Stabilising Selection and explain the difference aloud. Finally, take the Evolution quiz and come back to this page for any question you miss.
Selection favouring intermediate phenotypes, as seen in human birth weight.
🦎 EvolutionNew species arising within the same area, often through polyploidy or ecological specialisation.
🦎 EvolutionSelection favouring both extremes over the average, which may lead to divergence.
🦎 EvolutionSpeciation after a geographic barrier separates populations, as with Darwin's finches on separate islands.
🦎 Evolution