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The genetic paradox Neel sought to address was this: diabetes conferred a significant reproductive (and thus evolutionary) disadvantage to anyone who had it; yet the populations Neel studied had diabetes in such high frequencies that a genetic predisposition to develop diabetes seemed plausible.
However, environmental factors (almost certainly diet and weight) play a large part in the development of type 2 diabetes in addition to any genetic component. Genetic risk for type 2 diabetes changes as humans first began migrating around the world, implying a strong environmental component has affected the genetic-basis of type 2 diabetes.
The PPARGC1A gene regulates genes involved in energy metabolism. [1] [2] Since type 2 diabetes is characterized by chronic hyperglycaemia as a result of impaired pancreatic beta cell function [3] and insulin resistance in peripheral tissues, [4] it was thought that the gene might be downregulated in type 2 diabetes patients through DNA methylation.
The role of epigenetics in evolution is clearly linked to the selective pressures that regulate that process. As organisms leave offspring that are best suited to their environment, environmental stresses change DNA gene expression that is further passed down to their offspring, allowing for them also to better thrive in their environment.
Studies with monkeys show that injecting high-insulin-producing forms of these cells into the animals can “cure” type-1 diabetes for about six months. Human trials are underway.
Diabetes mellitus cases due to a known defect are classified separately. Type 2 diabetes is the most common type of diabetes mellitus accounting for 95% of diabetes. [2] Many people with type 2 diabetes have evidence of prediabetes (impaired fasting glucose and/or impaired glucose tolerance) before meeting the criteria for type 2 diabetes. [57]
Type 2 diabetes (T2D), formerly known as adult-onset diabetes, is a form of diabetes mellitus that is characterized by high blood sugar, insulin resistance, and relative lack of insulin. [6] Common symptoms include increased thirst , frequent urination , fatigue and unexplained weight loss . [ 3 ]
Evidence has been forwarded that environmental stimuli are important agents in the alteration of epigenes. Ironically, Darwinian evolution may act on these neo-Lamarckian acquired characteristics as well as the cellular mechanisms producing them (e.g. methyltransferase genes).