An oft-cited anecdote in support of the vitamin D hypothesis is that Arctic populations whose skin is relatively dark given their latitude, such as the Inuit and the Lapp, have had a diet that is historically rich in vitamin D. Sensitivity of modern humans to vitamin D deficiency is evident from the widespread occurrence of rickets in 19th-century industrial Europe, but whether dark-skinned humans migrating to polar latitudes tens or hundreds of thousands of years ago experienced similar problems is open to question. In any case, a risk for vitamin D deficiency can only explain selection for light skin. Among several mechanisms suggested to provide a selective advantage for dark skin in conditions of high UV irradiation (Loomis 1967; Robins 1991; Jablonski and Chaplin 2000), the most tenable are protection from sunburn and skin cancer due to the physical barrier imposed by epidermal melanin. Dark skin
All modern humans share a common ancestor who lived around 200,000 years ago in Africa. Comparisons between known skin pigmentation genes in chimpanzees and modern Africans show that dark skin evolved along with the loss of body hair about 1.2 million years ago and that this common ancestor had dark skin. Investigations into dark-skinned populations in South Asia and Melanesia indicate that skin pigmentation in these populations is due to the preservation of this ancestral state and not due to new variations on a previously lightened population. MC1R
The melanocortin 1 receptor (MC1R) gene is primarily responsible for determining whether pheomelanin and eumelanin are produced in the human body.
Dysuria refers to painful or uncomfortable urination.It is one of a constellation of irritative bladder symptoms (also sometimes referred to as lower urinary tract symptoms), which includes nocturia and urinary frequency. Diagnosis
The clinician should also look for physical findings of fever, rash, direct tenderness over the bladder area, and joint pain. Physical findings of increased temperature, increased pulse, low blood pressure in the presence of dysuria can indicate systemic infection. Urological obstruction due to stone or tumor can result in findings of hematuria, decreased urination, and bladder spasms. All these physical findings should be looked for carefully while obtaining history. History regarding recent sexual activity is crucial.Urinalysis is the most useful test to start the work up in a patient of dysuria. Urinalysis positive for nitrite carries a high predictive value of a positive urine culture. Also, urine dipstick showing leukocytes as equal predictive value as the presence of nitrites. When both are present, the predictive value goes even higher. If the patient only has leukocyte esterase or bacteria in the urine, then dysuria may suggest that the patient probably has urethritis. Differential diagnosis
This is typically described to be a burning or stinging sensation. It is most often a result of a urinary tract infection. It may also be due to an STD, bladder stones, bladder tumors, and virtually any condition of the prostate. It can also occur as a side effect of anticholinergic medication used for Parkinsons disease.