The study of heredity in biology is genetics. Genetics is the science of genes, heredity, and the variation of organisms. Some cats share common traits due to heredity. For cases where environment can influence heredity, see epigenetics. Lucretius treats male desire, female sexual pleasure, heredity, and infertility as aspects of sexual physiology. It can result from a complex combination of factors ranging from hormones to heredity. He was the discoverer of the Mendelian laws of heredity and hybridization. The temperament of dogs can be affected by different factors, including heredity, training, and socialization. There are many causes of this symptom, including heredity and bruising. The model for population stability resulted in Galton's formulation of the Law of Ancestral Heredity. He called this the theory of "Law of Ancestral Heredity". This led him to think that people are heavily influenced by heredity and their environment. Mendel began his studies on heredity using mice. They believed that one's heredity and social environment determine one's character. This provides support for the idea that dysthymia is caused in part by heredity.