TABLE 26.1 Types of reproductive isolating mechanisms Type Prezygotic Characteristics Acts before a zygote has formed Ecological Differences in habitat; individuals do not meet Temporal Reproduction takes place at different times Mechanical Anatomical differences prevent copulation Behavioral Differences in mating behavior prevent mating Gametic Gametes are incompatible or not attracted to each other Postzygotic Acts after a zygote has formed Hybrid inviability Hybrid zygote does not survive to reproduction Hybrid sterility Hybrid is sterile Hybrid breakdown F1 hybrids are viable and fertile, but F2 are inviable or sterile

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Sexual Motivation

Sexual motivation refers to a person's overall desire for sexual activity. It is an unusual motivation. Generally, among lower animals, the term 'drive' is commonly referred to as sexual motivation. It means a certain internal force drags the animal to be involved in reproductive behavior. On the contrary, humans are not simply driven by any internal force; rather, the sexual motivation in humans is due to several factors such as biological (hormones, genes), environmental (familial upbringing, chemical exposure) and physiological factors (culture, desire) which further determine engagement in sexual activities.