In the laboratory, chicken embryos and cultured cells are of great use to scientists. Most chickens have genes that are similar to those found in humans and, therefore, chicken cells may be utilized to achieve a better understanding of human biology and mammalian development in general. Chicken embryos are normally better suited to controlled studies than other laboratory animals, such as mice and rats, because they develop inside an egg rather than in the body of the mother. In fact, the relatively recent increase in the scientific use of chicken embryos may help reduce animal testing by replacing exposure trials on mice and rats.