Heritability: What It Means for Dogs (and What It Doesn't)

Heritability is a measure of how much of the variation in a trait, across a group of animals, comes from genetic differences between them rather than differences in their environments. It's a property of a group, not of one dog: a heritability of 0.25 for a behaviour doesn't mean a quarter of your dog's behaviour is genetic.

The short version

• About groups: heritability describes variation across a group of dogs, not any one dog.
• A scale from 0 to 1, often written as a percentage.
• It depends on the group: the same trait can have a different heritability in a different population or environment.
• Heritable isn't the same as fixed: training, care and experience still matter.
• Inherited isn't the same as heritable: a trait every dog shares can have a heritability near zero.

What heritability measures

Dogs in a group differ in a trait, such as body size or how they react to strangers. Some of that variation comes from genetic differences between the dogs, and some from differences in their environments and experiences. Heritability is the share that lines up with the genetic differences. A heritability near 1 means most of the variation in that group tracks genetics; near 0, most of it comes from elsewhere.

A classic illustration: almost every dog has four legs because of its genes, yet the heritability of leg number is close to zero. The rare dog with three legs usually lost one to injury, so the variation that exists is almost all environmental. Our guide to polygenic traits explains why most traits sit somewhere in between.

What dog studies have found

Behaviour is a good example. A 2019 study combined behavioural data from more than 14,000 dogs of 101 breeds with breed-averaged genetic data and found high heritability among breeds for 14 behavioural traits: differences in breeds' average behaviour lined up closely with how genetically similar the breeds were.

A 2022 study of more than 18,000 dogs found that most behavioural traits had a heritability above 25%, yet breed explained only about 9% of the variation in behaviour between individual dogs. The two findings fit together: genes do shape behaviour, but through many variants spread across dogs of all breeds, so a dog's breed tells you less about its personality than you might expect. Our guide to what a dog's breed means for daily care puts that into practice.

Common misreadings

• "Heritable means it can't change." It doesn't. A highly heritable trait can still respond to training, diet or care.
• "It tells you about my dog." It doesn't. Heritability describes variation in a group, not the make-up of one dog.
• "It's the same everywhere." It isn't. Change the population or the environment and the heritability can change too.
• "Low heritability means genes don't matter." Not necessarily, as the four-legs example shows.

Heritability and DNA results

A DNA report doesn't measure heritability, which is a research statistic for groups of dogs. But it hints at how much to expect from genetic predictions. Traits with a simple, mostly genetic basis, such as furnishings, are easier to predict from DNA than traits shaped by many genes and by experience, such as adult size or temperament. Our guide to whether DNA can predict adult size shows what that means in practice.