What does allometry mean?
Allometry is the biological principle that different parts of an organism grow at different rates, so that shape changes systematically as size increases. Coined in the early twentieth century by the biologist Julian Huxley and colleagues, the term describes scaling relationships that can often be captured by a simple power-law equation. A familiar illustration is human development: an infant's head is large relative to its body, but because the head grows more slowly than the limbs and torso, adult proportions look strikingly different. When a structure grows disproportionately faster than the whole — as with stag beetles' mandibles or deer antlers — biologists speak of positive allometry; when it grows more slowly, as with the brain relative to body mass in mammals, they speak of negative allometry. The word belongs to formal scientific register, appearing mainly in biology, paleontology, and morphology, but it captures an idea of broad intuitive appeal: growing up is not just getting bigger, it is changing shape.
nounThe study of how the size or proportions of parts of an organism change in relation to the size of the whole organism, or of another part, as it grows. More broadly, any scaling relationship between a biological variable and body size.
- The study or phenomenon of the relationship between the size of an organism (or one of its parts) and the size of another part or property — i.e., growth in which proportions are not constant.
- (By extension) Any mathematical scaling relationship between two measured quantities in biology, often expressed as a power law.
"The antlers of red deer grow with positive allometry, becoming disproportionately larger in bigger males."
"Researchers found that brain mass scales with negative allometry across many mammal species: larger animals have proportionally smaller brains."
"In his classic paper on crab claws, Huxley showed that claw weight follows a simple power-law equation of allometry relative to body weight."
Rarely pluralized; the plural appears only when referring to distinct allometric relationships or patterns, typically in scientific writing.
"The paper compared the allometries of limb length across three primate species."
The reason a baby's head looks huge compared to its body is allometry — human heads grow far more slowly than bodies do, so proportions shift dramatically from infancy to adulthood.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of allometry
Allometry derives from Greek roots: 'allo-' meaning 'other' or 'different' (as in 'allopathy' and 'allophone') combined with '-metry' meaning 'measurement' (from Greek 'metron', measure). The term was introduced in biological science in the early twentieth century, associated especially with the work of Julian Huxley on differential growth, whose 1932 book 'Problems of Relative Growth' helped establish it. Its counterpart 'isometry', using the root 'iso-' ('equal'), was formed along the same pattern for constant-proportion growth.
Related word forms
How allometry is actually used
A technical term used chiefly in biology, zoology, anthropology, and paleontology; rare in everyday speech. 'Positive allometry' means a part grows disproportionately faster than the whole, while 'negative allometry' means it grows more slowly. The related adjective is 'allometric'.
Easily confused with allometry
Isometry describes growth in which proportions remain constant (parts scale at the same rate as the whole), whereas allometry describes growth in which proportions change.
Anatomy is the general study of bodily structure; allometry is specifically the study of how relative sizes of body parts change with overall growth.