Puppies of all colours can potentially occur in the same litter. Colour is determined primarily by three genes. The first gene (the B locus) determines the density of the coat's eumelanin pigment granules, if that pigment is allowed: dense granules result in a black coat, sparse ones give a chocolate coat. They are a very intelligent breed. They are ranked No. 7 in Stanley Coren's The Intelligence of Dogs, making it one of the brightest dogs out of 138 breeds tested. In 2014, the UK breed survey reported an average lifespan for the Labrador Retriever of 12 years and 3 months, with some living up to 19 years of age.