Introduction Bronfenbrenner’s bioecological systems theory postulates that human development is the sum of factors of bioecological systems that are in an environment that one lives. The theory elucidates how bioecological systems influence human development throughout one’s lifespan, as it is extensively applicable in developmental psychology. Developmental psychology majorly entails the study of children’s behavior under strange circumstances and their interaction with adults. The theory views human development in the context of relationships that exist in bioecological systems of one’s environment. Bronfenbrenner (1994) argues that, human development occurs progressively through complex and reciprocal interactions between an individual and people, and objects and symbols that are in a given immediate environment (p.37). For interactions to be effective, they must be enduring and should occur in the immediate environment to form proximal processes that significantly influence human development. The proximal process exists in bioecological systems made of five spheres, namely microsystem, mesosystem, exosystem, macrosystem, and chronosystem. This essay describes four spheres of bioecological systems viz. microsystem, mesosystem, exosystem, and macrosystem, and analyzes the past and present biopsychosocial factors that influence human development. Microsystem Microsystem is the closest bioecological environment that directly influences human development. Microsystem consists of structures such as family, childcare, neighborhood, school, and workplace, which mainly form part of immediate bioecological environment. In microsystem, an individual experience regular interactions through relationships, routine activities, and social roles that elicit progressive and sustained interactions, which bring about human development. According to Bronfenbrenner (1994), proximal processes operate optimally in microsystem because it forms an immediate environment that elicit and sustain human development (p.39). Under microsystem level, family is a dominant structure that does not only influence child development but also development in adults. At microsystem level, relationships have a reciprocal influence that shape development of individuals in a given social structure. For instance, parents have the capacity to influence beliefs, behavior, and values of a child, and vice versa. Bioecological systems theory states that, reciprocal interactions are strongest at microsystem level, and they have the greatest impact on human development due to the proximity of bioecological factors. Family, as a social structure, significantly influenced my development during childhood because family members advised me on how to go about in life and become a successful person. For example, my mother loved me immensely in that she used to advise me regularly on how to have a decent discipline and work hard in my studies. Since I perceived that she loved me and wanted the best of me, I became determined not to let my mother down and thus I obeyed her advices to the letter. Then, I became an exceptionally courteous and industrious student in my class, which earned me warm reputation not only at school but also at home. Our relationship with my mother strengthened to the extent that, she would not deny me anything that I asked and on my part, I was so afraid to do anything that would disgrace he