The penis on a right whale can be up to – the testes, at up to in length, in diameter, and weighing up to 525 kg (1157 lbs), are also by far the largest of any animal on Earth. The blue whale may be the largest animal on the planet, yet the testicles of the right whale are ten times the size of those of the blue whale. They also exceed predictions in terms of relative size, as well – they are six times larger than would be expected on the basis of body mass. Together, the testicles make up nearly 1% of the right whale's total body weight. This strongly suggests sperm competition is important in mating, which correlates to the fact that right whales are highly promiscuous.