What decides how big a body gets? Growth is rapid in early life and then slows. Studies of mammals find that this slowdown comes from strong suppression of cell division in many tissues. It is driven mainly by local rather than body-wide mechanisms.

A good place to look is the growth plate. How fast a bone lengthens depends on how fast growth-plate cells swell into their large, hypertrophic form. The growing of hypertrophic cells is the biggest factor that sets how fast bones grow, and it largely explains why different bones grow at different rates. Swelling is also a cheap way to grow, because cells can enlarge quickly while lowering their energetic cost of growth.

The growth plate keeps itself in balance. Hypertrophic cells talk back to the resting zone through a PTHrP-Ihh negative feedback loop, which helps form columns of cells and keeps the plate's structure. Some resting-zone cells also act like stem cells. A group of them that makes PTHrP can renew itself and give rise to columns of growth-plate cells after birth.

Scientists can now follow single growth-plate cells to learn their fate. Single-cell gene readouts and lineage tracing in living animals let them study how resting-zone cells change into other cell types.

Organs seem to measure their own size. Skeletal and cardiac muscle growth are held back by a protein called myostatin, whose amount depends on muscle mass. Liver growth appears to follow bile acid flux, a sign of how the organ is working.

Height is controlled by many genes, each with a modest effect. As of November 2026, scientists have found more than 700 such gene variants, and some of them are in genes that affect cartilage in growth plates, but the roles of many height genes are still unknown. Because height depends on many gene variants plus the environment, it is hard to predict how tall a particular child will be. Different combinations passed from parents can make siblings differ in height.

A second source gives a different count. As of November 2026, a 2022 study of 5.4 million people from many ancestries found 12,111 gene markers linked to height, grouped into 7,209 regions. Its authors said the map is saturated for people of European ancestry, but more research is needed for other ancestries.

Environment matters as well as genes. A review from the US National Library of Medicine notes that moving to a country with better access to nutritious food and health care can substantially affect the height of the next generation of an immigrant family. As of November 2026, a study of 1,472 population surveys with more than 18.6 million people found South Korean women became 20.2 cm taller over a century and Iranian men 16.5 cm taller, with little change in some sub-Saharan African countries and South Asia.

The human brain uses a huge share of a child's energy. By calculating brain glucose use from birth to adulthood, researchers found it peaks in childhood at the equivalent of 66% of the body's resting metabolism and 43% of its daily energy needs. Brain energy demand and body growth rate vary inversely across development, which supports the hypothesis that the high cost of brain development requires slower body growth.

Not every primate pays the same brain cost. Synapse density in the brain peaks in infancy for macaques but in childhood for humans and chimpanzees. So growth is predicted to slow in chimpanzee juveniles to a lesser degree than in humans.

So why does growth stop at an adult size? It is still being worked out. One review suggests that the slowdown does not depend only on time but on growth itself, so adult size is limited by a negative feedback loop, with different organs using different cues.

Words to know

• hypertrophic: swollen large
• myostatin: muscle growth brake
• variants: gene versions
• synapse: brain link