Mas, as significativas mutações benéficas aleatórias (as específicas, na espécie humana, a que eu já me referi) jamais foram reproduzidas e jamais foram sequer simuladas computacionalmente (mesmo porque não se tem a mínima ideia necessária de como realmente tais supostas mutações benéficas tenham supostamente acontecido, é algo extremamente vago e hipotético).
Você poderia apontar quais genes são esses especificamente, e porque considera que seja improvável que essas variações humanas sejam resultado de mutação?
Mas, este é justamente um dos pontos falhos que estou apontando, os biólogos históricos não tem a mínima ideia de quais seriam estes genes. São suposições bastante vagas.
Isso que está dizendo nem faz sentido.
Os biólogos dispõem do genoma humano, de um bocado de variações deles, e dos genomas de chimpanzés, e acho que outros hominídeos também. Então é perfeitamente possível dizer quais são os alelos que diferem especificamente em humanos.
Em alguns casos específicos, é possível que tenham sido feitos estudos visando saber em que o gene atua, ou até tentar datar sua origem.
Não há qualquer notícia de que haja genes "especiais" no ser humano que não possam ser produto de mutações ordinárias nos genes homólogos de outros primatas aparentados.
https://www.scientificamerican.com/article/tiny-genetic-differences-between-humans-and-other-primates-pervade-the-genome/Quanto ao porque que parece ser tão improvável, é porque não se tem observado tais mutações benéficas aleatórias (e significativas) acontecerem em seres humanos (ou outros de complexidade semelhante), se tais mutações aleatórias benéficas estivessem sendo observadas (mesmo umas poucas no século passado no qual nasceram bilhões de humanos), então já seria um bom indício de sua real possibilidade de ocorrência no vago e distante passado, mas cadê ?
A impressão que passa é que você acha que mutação é algo meio como X-men. Na verdade, toda diferença que existe entre pessoas que não sejam gêmeos idênticos, é originária de mutações (e mesmo algumas entre estes). Para saber se/quando são "benéficas e significativas" será mais complicado, e não será mesmo o caso na maior parte do tempo.
Em vez de coisas como "ter asas", ou soltar raios laser pelos olhos, as mutações benéficas vão causar coisas como pele mais clara ou mais escura (sendo relativo o quando/onde isso é benéfico), ou conferir persistência a lactase (permitindo as pessoas digerirem leite depois de adultas), ter menos pêlos no corpo, mais ou menos glândulas de suor, alguma diferença no funcionamento cerebral, alguma diferença imunológica, etc.
https://www.nature.com/news/massive-genetic-study-shows-how-humans-are-evolving-1.22565http://www.sciencemag.org/news/2016/05/humans-are-still-evolving-and-we-can-watch-it-happenGenetic variation in taste and its influence on food selection.
Garcia-Bailo B1, Toguri C, Eny KM, El-Sohemy A.
Author information
Abstract
Taste perception plays a key role in determining individual food preferences and dietary habits. Individual differences in bitter, sweet, umami, sour, or salty taste perception may influence dietary habits, affecting nutritional status and nutrition-related chronic disease risk. In addition to these traditional taste modalities there is growing evidence that "fat taste" may represent a sixth modality. Several taste receptors have been identified within taste cell membranes on the surface of the tongue, and they include the T2R family of bitter taste receptors, the T1R receptors associated with sweet and umami taste perception, the ion channels PKD1L3 and PKD2L1 linked to sour taste, and the integral membrane protein CD36, which is a putative "fat taste" receptor. Additionally, epithelial sodium channels and a vanilloid receptor, TRPV1, may account for salty taste perception. Common polymorphisms in genes involved in taste perception may account for some of the interindividual differences in food preferences and dietary habits within and between populations. This variability could affect food choices and dietary habits, which may influence nutritional and health status and the risk of chronic disease. This review will summarize the present state of knowledge of the genetic variation in taste, and how such variation might influence food intake behaviors.
Diet and the evolution of human amylase gene copy number variation.
Perry GH1, Dominy NJ, Claw KG, Lee AS, Fiegler H, Redon R, Werner J, Villanea FA, Mountain JL, Misra R, Carter NP, Lee C, Stone AC.
Author information
Abstract
Starch consumption is a prominent characteristic of agricultural societies and hunter-gatherers in arid environments. In contrast, rainforest and circum-arctic hunter-gatherers and some pastoralists consume much less starch. This behavioral variation raises the possibility that different selective pressures have acted on amylase, the enzyme responsible for starch hydrolysis. We found that copy number of the salivary amylase gene (AMY1) is correlated positively with salivary amylase protein level and that individuals from populations with high-starch diets have, on average, more AMY1 copies than those with traditionally low-starch diets. Comparisons with other loci in a subset of these populations suggest that the extent of AMY1 copy number differentiation is highly unusual. This example of positive selection on a copy number-variable gene is, to our knowledge, one of the first discovered in the human genome. Higher AMY1 copy numbers and protein levels probably improve the digestion of starchy foods and may buffer against the fitness-reducing effects of intestinal disease.
Convergent adaptation of human lactase persistence in Africa and Europe.
Tishkoff SA1, Reed FA, Ranciaro A, Voight BF, Babbitt CC, Silverman JS, Powell K, Mortensen HM, Hirbo JB, Osman M, Ibrahim M, Omar SA, Lema G, Nyambo TB, Ghori J, Bumpstead S, Pritchard JK, Wray GA, Deloukas P.
Author information
Abstract
A SNP in the gene encoding lactase (LCT) (C/T-13910) is associated with the ability to digest milk as adults (lactase persistence) in Europeans, but the genetic basis of lactase persistence in Africans was previously unknown. We conducted a genotype-phenotype association study in 470 Tanzanians, Kenyans and Sudanese and identified three SNPs (G/C-14010, T/G-13915 and C/G-13907) that are associated with lactase persistence and that have derived alleles that significantly enhance transcription from the LCT promoter in vitro. These SNPs originated on different haplotype backgrounds from the European C/T-13910 SNP and from each other. Genotyping across a 3-Mb region demonstrated haplotype homozygosity extending >2.0 Mb on chromosomes carrying C-14010, consistent with a selective sweep over the past approximately 7,000 years. These data provide a marked example of convergent evolution due to strong selective pressure resulting from shared cultural traits-animal domestication and adult milk consumption.
Natural selection and molecular evolution in PTC, a bitter-taste receptor gene.
Wooding S1, Kim UK, Bamshad MJ, Larsen J, Jorde LB, Drayna D.
Author information
Abstract
The ability to taste phenylthiocarbamide (PTC) is a classic phenotype that has long been known to vary in human populations. This phenotype is of genetic, epidemiologic, and evolutionary interest because the ability to taste PTC is correlated with the ability to taste other bitter substances, many of which are toxic. Thus, variation in PTC perception may reflect variation in dietary preferences throughout human history and could correlate with susceptibility to diet-related diseases in modern populations. To test R. A. Fisher's long-standing hypothesis that variability in PTC perception has been maintained by balancing natural selection, we examined patterns of DNA sequence variation in the recently identified PTC gene, which accounts for up to 85% of phenotypic variance in the trait. We analyzed the entire coding region of PTC (1,002 bp) in a sample of 330 chromosomes collected from African (n=62), Asian (n=138), European (n=110), and North American (n=20) populations by use of new statistical tests for natural selection that take into account the potentially confounding effects of human population growth. Two intermediate-frequency haplotypes corresponding to "taster" and "nontaster" phenotypes were found. These haplotypes had similar frequencies across Africa, Asia, and Europe. Genetic differentiation between the continental population samples was low (FST=0.056) in comparison with estimates based on other genes. In addition, Tajima's D and Fu and Li's D and F statistics demonstrated a significant deviation from neutrality because of an excess of intermediate-frequency variants when human population growth was taken into account (P<.01). These results combine to suggest that balancing natural selection has acted to maintain "taster" and "nontaster" alleles at the PTC locus in humans.
