Reduction division, more commonly known as meiosis, is the specialized cell division process that reduces the chromosome number by half. This ensures that when a sperm and egg fuse during fertilization, the resulting zygote has the correct diploid number of chromosomes, maintaining genetic consistency across generations.

Erik Erikson (often spelled Erickson in some texts) proposed the theory of psychosocial development, which outlines eight stages of human development from infancy to late adulthood. Each stage involves a specific crisis that must be resolved to develop healthy personality traits.

Gender identity is defined as an individual's internal, deeply held sense of their own gender. It is a psychological construct distinct from biological sex or social gender roles, representing how a person perceives themselves on the spectrum of male, female, or other gender identities.

Developmental psychology views human growth as a lifelong process, often referred to as the lifespan perspective. Development does not cease at a specific age; rather, it involves continuous change, adaptation, and growth across physical, cognitive, and psychosocial domains from infancy through old age. The assertion that development stops at old age is incorrect because individuals continue to experience psychological and social transitions throughout their entire lives.

In humans, biological sex is determined by the sex chromosomes. Females typically possess two X chromosomes (XX), while males typically possess one X chromosome and one Y chromosome (XY). The presence of the Y chromosome is the primary genetic trigger for the development of male anatomical characteristics during prenatal development.

The average duration of human gestation is approximately 38 weeks from the time of conception, which equates to roughly 40 weeks from the first day of the last menstrual period. Medical literature often cites 38 weeks as the actual fetal age, confirming the accuracy of the provided answer in a biological context.

A teratogen is any agent, such as a chemical, virus, or radiation, that can cause birth defects or developmental abnormalities in an embryo or fetus. Nicotine, radiation, and alcohol are well-documented teratogens. While hormones can affect development, testosterone is a naturally occurring endogenous hormone and is not typically categorized as a teratogen in the same context as environmental toxins.

Smoking during pregnancy introduces toxins like nicotine and carbon monoxide, which restrict oxygen supply to the fetus. This is scientifically linked to intrauterine growth restriction, resulting in lower birth weight and a statistically higher risk of infant mortality.

Lawrence Kohlberg's research on moral development was comprehensive, involving participants across various age groups. By presenting moral dilemmas to children, adolescents, and adults, he was able to map out the progression of moral reasoning through his proposed stages, demonstrating how individuals evolve from simple obedience to complex ethical principles over the course of their lifespan.

Baumrind identified the authoritative parenting style as the most effective. This style balances high levels of warmth and responsiveness with clear, consistent expectations and firm boundaries. Children raised by authoritative parents tend to exhibit higher self-esteem, better social skills, and greater academic success compared to those raised with authoritarian or permissive styles.