Which of the followig traits in humans is an example of physiological variation?

Analyze the question: The question asks which trait is an example of physiological variation in humans.

Concept: Variation among individuals of a species can be:

• Morphological (structural) variation: differences in physical form or appearance that can be seen or measured, e.g. height, skin colour, fingerprints, body mass.
• Physiological variation: differences in how the body functions or in its ability to perform a function, e.g. the ability to roll the tongue, blood group, ability to taste PTC, sickle cell trait, and metabolic rate.

Working through the options:

• A. Skin colour: a visible physical feature, so it is morphological.
• B. Fingerprint: the pattern of ridges is a structural feature, so it is morphological.
• C. Tongue rolling: this is the ability to perform a function (curling the tongue into a U-shape). It is a functional difference, so it is physiological. It is also a discontinuous variation, because you either can roll your tongue or you cannot.
• D. Height: this is measurable body size, so it is morphological. It is also a continuous variation.

Answer: Tongue rolling is the only option that describes a difference in ability or function rather than physical structure.

Exam tip: Ask yourself, "Can I see or measure it as a physical feature, or is it about what the body can do?" If you can see or measure it, it is morphological. If it is an ability, such as tongue rolling, taste ability, or blood group, it is physiological.