Adaptation Facts
Since Charles Darwin's "On the Origin of Species," biologists and anthropologists have deliberated over the process of human development: Is natural selection random or deliberate? Stanford geneticists believe they have settled the argument. Recent publication of their findings in the "Public Library of Science Genetics" evince that while all genetic mutations may appear to begin arbitrarily, an organisms beneficial changes to environmental conditions are "directly selected for and quickly perpetuate throughout the population."
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Process and Occurance
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When an organism redesigns its structure to endure its ecosystem, adaptation takes place. Crucial to survival, the adaptation process enables organisms to adjust to suit that ecosystem, and so to survive. Individual organisms adapt in several ways--through genetic mutations, acclimatization, sensory and developmental changes, and physiological responses or through cultural and technological advances. When genetic mutations survive procreation over generations, biological integration of the new, dominant genes produces species adaptation. The combination of genetic mutations that survive long enough to pass to a new generation provide the framework for the new adaptation.
Genetic Adaptation
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Environmental stresses that last over generations contribute to genetic adaptation. Individuals within the species that inherit an advantageous genetic mutation are more likely to survive and pass the trait on to the next generation, spreading it throughout the species over time. This is the process of simple natural selection. For example, a human group exposed to a specific disease organism, over time, pass on the traits of the survivors, giving successive generations a degree of immunity to the disease.
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Acclimatization
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Anatomical or physiological adjustments to seasonal or even decades of an environmental stress factor help people acclimate to stresses to survive. Acclimatization typically is reversible. For instance, humans produce more melanin--skin pigment--in response to seasonal ultraviolet radiation, and then lose the excess pigmentation during winter months.
Sensory Adaptation
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A physical change in sensory organs responding to stimuli is sensory adaptation. When the pupil of the eye adjusts to various degrees of light, it becomes accustomed to that degree of sensation. Constant levels of stimulation no longer produce an adaptation, but any abrupt change requires more adaptation.
Developmental Adaptation
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A change in growth patterns, or physiology in response to environmental stress is developmental adaptation. Typically, this occurs during primary growth periods, such as childhood or puberty with the resultant changes being irreversible. The custom of wrapping feet to keep them from growing---such as was popular in Asia in past generations---is a form of developmental adaptation.
Physiological Adaptation
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Responses to hormonal triggers are physiological adaptations that may be momentary, or may eventually produce a permanent adaptation. Examples include adrenalin-produced responses such as rapid breathing, abnormal feats of strength or increased heart rate. Constant hormonal stimuli encourage permanent physical responses and adaptations that may compromise the organism rather than improve its function. Examples are weight gain in response to adrenalin or hypoglycemia in response to insulin.
Culture and Technology
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Humans improve their ability to adapt to an intemperate environment using culture and technology. Discovering fire and clothing allowed adaptation to colder climates and inventions such as irrigation allowed humans to produce food in arid locations. Humans also impose controls on natural urges and reflexes through psychological conditioning and societal codes.
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References
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