Evolutionary neuropathology

Evolutionary neuropathology is an approach to understanding neurological and neurodegenerative diseases in terms of adaptation to environment, natural history and evolutionary medicine. Conceptually, it overlaps with a number of areas in theoretical biology, such as evolutionary developmental psychopathology, which explains psychiatric disorders within an evolutionary context. Articles in evolutionary neuropathology point out that the genes responsible for a large number of neurological disorders may have been naturally selected due to adaptive qualities that they conferred in the ancestral environment. Disorders such as Schizophrenia (Reser, 2007 [Reser, J.E. (2007)Schizophrenia and phenotypic plasticity: Schizophrenia may represent a predictive, adaptive response to severe environmental adversity that allows both bioenergetic thrift and a defensive behavioral strategy. "Medical Hypotheses". 69 [2] : 383-394. [http://www.ncbi.nlm.nih.gov/sites/entrez?Db=pubmed&Cmd=ShowDetailView&TermToSearch=17321061&ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum=Citation PubMed] ] ), Down Syndrome (Reser, 2006 [Reser, J.E. (2006)Evolutionary neuropathology and Down syndrome: An analysis of the etiological and phenotypical characteristics of Down syndrome suggests that it may represent an adaptive response to severe maternal deprivation. "Medical Hypotheses". 67 [3] : 474-481. [http://www.ncbi.nlm.nih.gov/sites/entrez?Db=pubmed&Cmd=ShowDetailView&TermToSearch=16737781&ordinalpos=2&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum=Citation PubMed] ] ), a number of forms of mental retardation (Reser, 2006 [Reser, J.E. (2006) Evolutionary neuropathology & congenital mental retardation: Environmental cues predictive of maternal deprivation influence the fetus to minimize cerebral metabolism in order to express bioenergetic thrift "Medical Hypotheses". 67 [3] : 529-544. [http://www.ncbi.nlm.nih.gov/sites/entrez?Db=pubmed&Cmd=ShowDetailView&TermToSearch=16644141&ordinalpos=3&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum=Citation PubMed] ] ), Alzheimer's disease and many other neurological diseases are conceptualized as protective responses to environmental adversity. It is pointed out that these disorders may be adaptively programmed by early nutritional scarcity, in the form of a predictive adaptive response, permitting physiological and behavioral characteristics that would have led to increased survival and thereby, reproductive success. Individuals with these disorders all exhibit low cerebral metabolic rates and each may have been well suited, ecologically, for a deprived or nutritionally scarce environment.

These hypotheses are often considered relative to the thrifty phenotype paradigm according to which adverse prenatal events can alter normal patterns of gene expression resulting in an individual that is better suited, metabolically, for a deprived environment. Malnourished mothers have been shown to have an increased propensity to give birth to offspring that feature a “thrifty phenotype,” permitting low calorie utilization, increased fat deposition and sedentary nature, but at times, resulting in obesity, diabetes and cardiovascular disease (Hales & Barker, 1992 [Hales, C.N., & Barker, D.J. (1992). Type 2 (non-insulin-dependent) diabetes mellitus: the thrifty phenotype hypothesis. "Diabetologia". 35: 595-601. [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1644236&dopt=Citation PubMed] ] ). Because the risk factors for many forms of neurological disease include prenatal occurrences such as maternal malnourishment, low birth weight, multiparity, short birth interval, advanced maternal age and maternal stress, they may be examples of thrifty, epigenetic programming acting on the brain.

The forms of neuropathology discussed do not cause damage to vital neurological systems- most simply decrease the volume and glucose expenditure of the cerebral cortex and hippocampus- the same areas that are known to become adaptively hypometabolic in response to variations in ecological rigor in birds and mammals. Also, many disorders that present comorbidly with neuropathology, such as tendency toward obesity, decrement in anabolic hormones, hypotonic musculature, up-regulation of the hypothalamic-pituitary-adrenal axis, and decreased thyroid output are associated with energy conservancy and the thrifty phenotype.

It is noted that many neurological disorders cause social and vocational deficits in modern times, but may have allowed metabolic thriftiness and self sufficiency in prehistoric times. Interestingly, those with the disorders may have been well adapted to take up an ecological niche that closely resembled the less skill-intensive niche of our less encephalized, primate ancestors. Determining the relative impact of evolutionary causation on neuropathological disease should inform medical treatment modalities and help researchers more accurately identify the risk factors responsible for neurological disease.

ee also

*Evolutionary developmental psychology
*Evolutionary physiology
*Evolutionary psychology
*Phenotypic plasticity
*Trivers-Willard hypothesis
*Thrifty gene hypothesis

References