Twin studies are research methods used to understand the influence of genetics and environment on human traits and behaviors. By comparing identical twins, who share nearly all their genes, with fraternal twins, who share about half, researchers can determine how much of a trait is inherited versus influenced by surroundings. These studies often focus on various aspects, such as intelligence, personality, and mental health. Findings from twin studies have contributed significantly to fields like psychology and genetics, helping scientists understand the complex interplay between nature and nurture in shaping who we are.