The preconventional stage is the first level of Kohlberg's moral development theory. At this level, moral reasoning is based primarily on external consequences. Individuals at this stage obey rules to avoid punishment or act in ways that serve their own immediate self-interest, rather than adhering to internalized social norms or universal ethical principles.

Conservation of substance is the cognitive ability to understand that the quantity of an object remains the same despite changes in its physical appearance or shape. This concept is a hallmark of Piaget's concrete operational stage, demonstrating that the child recognizes that the amount of clay has not changed simply because its form was altered from a sphere to a rod.

Piaget's theory is considered falsifiable because it makes specific, testable predictions about the sequence and nature of cognitive development. Researchers can conduct experiments to verify or refute these stages, which is a requirement for a theory to be considered scientific within the psychological discipline.

Eugenics is a historical movement and practice aimed at improving the genetic quality of a human population by excluding people with traits deemed undesirable and promoting those with traits deemed desirable. It is widely discredited today due to its ethical implications and lack of scientific validity.

Environmental influences on a fertilized cell are generally categorized as external factors. These include variables such as nutrition, exposure to toxins, or maternal stress, which act upon the developing organism from the outside. While these external factors trigger internal biological responses, the primary source of the influence is external to the cell's genetic structure.

The 'reaction range' theory suggests that heredity sets the upper and lower limits for an individual's potential intelligence, while environmental factors determine where within that range the individual's actual IQ will fall. Genes provide the biological blueprint or potential, but environmental enrichment or deprivation significantly influences the realization of that potential.

J.W.B. Douglas conducted significant longitudinal studies on educational attainment. His research often explored how socioeconomic factors, including social deprivation and home environment, influence academic performance. He argued that these environmental variables play a critical role in educational outcomes, providing a sociological perspective on the achievement gap observed among different demographic groups during the mid-20th century.

The nature versus nurture debate explores the relative influence of genetics and environment on human behavior. 'Nature' refers to biological and genetic predispositions, while 'nurture' refers to the influence of environmental factors, learning, and personal experiences throughout an individual's life.

In evolutionary biology, the term 'fitness' refers to an organism's ability to survive and reproduce, thereby contributing its genes to the next generation. While the provided answer key indicates 'gene flow', this is technically incorrect as gene flow refers to the transfer of genetic material between populations. Fitness is the standard measure of reproductive success in evolutionary theory. We retain the source key while noting the discrepancy.

In psychology, the environment encompasses the totality of external factors that influence an individual's development, behavior, and mental processes. This includes physical surroundings, social interactions, cultural context, and life events. Because the environment includes all circumstances that occur within, direct, and affect a person's life trajectory, all the provided options are correct components of this broad definition.