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Brain Development  

Robbin Gibb

The process of brain development begins shortly after conception and in humans takes decades to complete. Indeed, it has been argued that brain development occurs over the lifespan. A complex genetic blueprint provides the intricate details of the process of brain construction. Additional operational instructions that control gene and protein expression are derived from experience, and these operational instructions allow an individual to meet and uniquely adapt to the environmental demands they face. The science of epigenetics provides an explanation of how an individual’s experience adds a layer of instruction to the existing DNA that ultimately controls the phenotypic expression of that individual and can contribute to gene and protein expression in their children, grandchildren, and ensuing generations. Experiences that contribute to alterations in gene expression include gonadal hormones, diet, toxic stress, microbiota, and positive nurturing relationships, to name but a few. There are seven phases of brain development and each phase is defined by timing and purpose. As the brain proceeds through these genetically predetermined steps, various experiences have the potential to alter its final form and behavioral output. Brain plasticity refers to the brain’s ability to change in response to environmental cues or demands. Sensitive periods in brain development are times during which a part of the brain is particularly malleable and dependent on the occurrence of specific experiences in order for the brain to tune its connections and optimize its function. These periods open at different time points for various brain regions and the closing of a sensitive period is dependent on the development of inhibitory circuitry. Some experiences have negative consequences for brain development, whereas other experiences promote positive outcomes. It is the accumulation of these experiences that shape the brain and determine the behavioral outcomes for an individual.


Nature and Nurture as an Enduring Tension in the History of Psychology  

Hunter Honeycutt

Nature–nurture is a dichotomous way of thinking about the origins of human (and animal) behavior and development, where “nature” refers to native, inborn, causal factors that function independently of, or prior to, the experiences (“nurture”) of the organism. In psychology during the 19th century, nature-nurture debates were voiced in the language of instinct versus learning. In the first decades of the 20th century, it was widely assumed that that humans and animals entered the world with a fixed set of inborn instincts. But in the 1920s and again in the 1950s, the validity of instinct as a scientific construct was challenged on conceptual and empirical grounds. As a result, most psychologists abandoned using the term instinct but they did not abandon the validity of distinguishing between nature versus nurture. In place of instinct, many psychologists made a semantic shift to using terms like innate knowledge, biological maturation, and/or hereditary/genetic effects on development, all of which extend well into the 21st century. Still, for some psychologists, the earlier critiques of the instinct concept remain just as relevant to these more modern usages. The tension in nature-nurture debates is commonly eased by claiming that explanations of behavior must involve reference to both nature-based and nurture-based causes. However, for some psychologists there is a growing pressure to see the nature–nurture dichotomy as oversimplifying the development of behavior patterns. The division is seen as both arbitrary and counterproductive. Rather than treat nature and nurture as separable causal factors operating on development, they treat nature-nurture as a distinction between product (nature) versus process (nurture). Thus there has been a longstanding tension about how to define, separate, and balance the effects of nature and nurture.


Integrated Theories of Biological Aging  

Conscience P. Bwiza, Jyung Mean Son, and Changhan Lee

Aging is a progressive process with multiple biological processes collectively deteriorating with time, ultimately causing loss of physiological functions necessary for survival and reproduction. It is also thought to have a strong evolutionary basis, largely resulting from the lack of selection force. Here, we discuss the evolutionary aspects of aging and a selection of theories founded on a variety of biological functions that have been shown to be involved in aging in multiple model organisms, ranging from the simple yeast, worms, flies, killifish, and rodents, to non-human primates and humans. The conglomerate of distinct theories has together revolutionized aging research in the past several decades, far more than what humankind has known since the dawn of civilization. However, not one theory alone can independently explain aging and should not be interpreted out of context of the cell and organism in its entirety. That said, the 21st century has been and will be an exciting time in the field of aging, with scientific advances on health span and lifespan being made at multiple fronts of biology and medicine in an unprecedented scale.