The Genetic Diversity of the Americas.

The history of the Americas involved the encounter of millions of Native Americans, Europeans, and Africans. A variable admixture of these three continental groups has taken place throughout the continent, influenced by demography and a range of social factors. This variable admixture has had a major influence on the genetic makeup of populations across the continent. Here, we summarize the demographic history of the region, highlight some social factors that affected historical admixture, and review major patterns of ancestry across the Western Hemisphere based on genetic data.

The impact of arteriovenous fistulae on the myocardium: the impact of creation and ligation in the transplant era.

Cardiac hypertrophy is a relatively common complication seen in patients with advanced chronic kidney disease (CKD) and end-stage renal disease (ESRD). Moreover, cardiac hypertrophy is even more frequently seen in patients with ESRD who have an arteriovenous (AV) access. There has been substantial evidence pertaining to the effects of AV access creation on the heart structure and function. Similarly, there is increasing evidence on the effects of AV access closure, flow reduction, transplantation, and immunosuppressive medication on both endpoints. In this review, we present the evidence available in the literature on these topics and open the dialog for further research in this interesting field.

Small molecule agonists of integrin CD11b/CD18 do not induce global conformational changes and are significantly better than activating antibodies in reducing vascular injury.

BACKGROUND: CD11b/CD18 is a key adhesion receptor that mediates leukocyte adhesion, migration and immune functions. We recently identified novel compounds, leukadherins, that allosterically enhance CD11b/CD18-dependent cell adhesion and reduce inflammation in vivo, suggesting integrin activation to be a novel mechanism of action for the development of anti-inflammatory therapeutics. Since a number of well-characterized anti-CD11b/CD18 activating antibodies are currently available, we wondered if such biological agonists could also become therapeutic leads following this mechanism of action. METHODS: We compared the two types of agonists using in vitro cell adhesion and wound-healing assays and using animal model systems. We also studied effects of the two types of agonists on outside-in signaling in treated cells. RESULTS: Both types of agonists similarly enhanced integrin-mediated cell adhesion and decreased cell migration. However, unlike leukadherins, the activating antibodies produced significant CD11b/CD18 macro clustering and induced phosphorylation of key proteins involved in outside-in signaling. Studies using conformation reporter antibodies showed that leukadherins did not induce global conformational changes in CD11b/CD18 explaining the reason behind their lack of ligand-mimetic outside-in signaling. In vivo, leukadherins reduced vascular injury in a dose-dependent fashion, but, surprisingly, the anti-CD11b activating antibody ED7 was ineffective. CONCLUSIONS: Our results suggest that small molecule allosteric agonists of CD11b/CD18 have clear advantages over the biologic activating antibodies and provide a mechanistic basis for the difference. GENERAL SIGNIFICANCE: CD11b/CD18 activation represents a novel strategy for reducing inflammatory injury. Our study establishes small molecule leukadherins as preferred agonists over activating antibodies for future development as novel anti-inflammatory therapeutics.

c-Kit signaling determines neointimal hyperplasia in arteriovenous fistulae.

Stenosis of arteriovenous (A-V) fistulae secondary to neointimal hyperplasia (NIH) compromises dialysis delivery, which worsens patients' quality of life and increases medical costs associated with the maintenance of vascular accesses. In the present study, we evaluated the role of the receptor tyrosine kinase c-Kit in A-V fistula neointima formation. Initially, c-Kit was found in the neointima and adventitia of human brachiobasilic fistulae, whereas it was barely detectable in control veins harvested at the time of access creation. Using the rat A-V fistula model to study venous vascular remodeling, we analyzed the spatial and temporal pattern of c-Kit expression in the fistula wall. Interestingly, c-Kit immunoreactivity increased with time after anastomosis, which concurred with the accumulation of cells in the venous intima. In addition, c-Kit expression in A-V fistulae was positively altered by chronic kidney failure conditions. Both blockade of c-Kit with imatinib mesylate (Gleevec) and inhibition of stem cell factor production with a specific short hairpin RNA prevented NIH in the outflow vein of experimental fistulae. In agreement with these data, impaired c-Kit activity compromised the development of NIH in A-V fistulae created in c-KitW/Wv mutant mice. These results suggest that targeting of the c-Kit signaling pathway may be an effective approach to prevent postoperative NIH in A-V fistulae.

Myofibroblasts: the ideal target to prevent arteriovenous fistula failure?

The arteriovenous fistula (AVF) failure is a major cause of morbidity in the hemodialysis population. Most AVFs fail due to neointimal hyperplasia (NIH). In this issue, Yang et al. delineated a mechanism responsible for transforming the fistula adventitia into a fertile soil for neointimal precursors. These authors pondered the role of hypoxia-regulated hypoxia-inducible factor-1 (HIF-1α), vascular endothelial growth factor A (VEGF-A), and matrix metalloproteinases (MMPs) in the activation of those adventitial myofibroblasts that may significantly contribute to the formation of the fistula neointima.

Dry food affects the oxidative/antioxidant profile of dogs.

BACKGROUND: Including adequate concentrations of antioxidants in dog diets has been recommended to reduce their vulnerability to the action of free radicals and reactive oxygen species (ROS). Oxidative stress in dogs has been associated with a wide range of diseases and disorders, as well as with ageing. There are few reports about the influence of diet on dog's antioxidant profile and oxidative stress. OBJECTIVE: The objective of this study was to evaluate the effect of four types of dry dog food on the oxidative/antioxidant profile of dogs. METHODS: Six Beagle dog males were used. The study included four experimental diets (dry foods A-D). Each dry food was supplied for 5 weeks to all dogs, for a total of 24 weeks, including an adaptation week between one food and another. For each dry dog food, the total phenolic content (TPC), total antioxidant capacity (TAC) and cytotoxicity were evaluated. Each week, a blood sample was collected to measure ROS and TAC of plasma. A crossover repeated measures design was used. Mixed models were adjusted, and means were compared using the Tukey test. RESULTS: Food A had the highest values for TPC and TAC. Food C had the lowest levels of ROS, whereas food B had the highest TAC in the blood plasma. The dog had a significant influence on the redox state of its blood plasma, even when the same dog was fed the different dry foods. CONCLUSION: Dry dog food influences the oxidative/antioxidant profile of dog's blood plasma; however, this seems to be unrelated to the antioxidant profile of the food.

Assessing microhabitat, landscape features and intraguild relationships in the occupancy of the enigmatic and threatened Andean tiger cat (Leopardus tigrinus pardinoides) in the cloud forests of northwestern Colombia.

Mesocarnivores play a key role in ecosystem dynamics through the regulation of prey populations and are sensitive to environmental changes; thus, they are often considered good model organisms for conservation planning. However, data regarding the factors that influence the habitat use of threatened small wild felids such as the Andean tiger cat (Leopardus tigrinus pardinoides) are scarce. We conducted a two-year survey with 58 camera trap stations to evaluate the determinants of Andean tiger cat habitat use in three protected areas in the Middle Cauca, Colombia. We developed site occupancy models and found that Andean tiger cat habitat use increased with leaf litter depth at intermediate elevations and far from human settlements. Through conditional cooccurrence models, we found that Andean tiger cat habitat use was invariant to the presence of prey or potential intraguild competitors and killers/predators, but its detectability increased when they were present and detected. This suggests that Andean tiger cats may be more likely to be detected in sites with high prey availability. We found that Andean tiger cats preferred sites with deep leaf litter, which is a particular feature of cloud forests that provides suitable conditions for ambush hunting and hiding from intraguild enemies. Our results showed that Andean tiger cats avoided human settlements, which may minimize potential mortality risks in those areas. Moreover, the restricted use of middle elevations by Andean tiger cats suggested that they could be used as a sentinel species to track the effects of climate change since their suitable habitat is likely to be projected upward in elevation. Future conservation actions must be focused on identifying and mitigating human-related threats close to the Andean tiger cat habitat while preserving microhabitat conditions and the existing networks of protected areas.

Sodium-calcium exchanger-3 regulates pain "wind-up": From human psychophysics to spinal mechanisms.

Repeated application of noxious stimuli leads to a progressively increased pain perception; this temporal summation is enhanced in and predictive of clinical pain disorders. Its electrophysiological correlate is "wind-up," in which dorsal horn spinal neurons increase their response to repeated nociceptor stimulation. To understand the genetic basis of temporal summation, we undertook a GWAS of wind-up in healthy human volunteers and found significant association with SLC8A3 encoding sodium-calcium exchanger type 3 (NCX3). NCX3 was expressed in mouse dorsal horn neurons, and mice lacking NCX3 showed normal, acute pain but hypersensitivity to the second phase of the formalin test and chronic constriction injury. Dorsal horn neurons lacking NCX3 showed increased intracellular calcium following repetitive stimulation, slowed calcium clearance, and increased wind-up. Moreover, virally mediated enhanced spinal expression of NCX3 reduced central sensitization. Our study highlights Ca2+ efflux as a pathway underlying temporal summation and persistent pain, which may be amenable to therapeutic targeting.

Prediction of eye, hair and skin colour in Latin Americans.

Here we evaluate the accuracy of prediction for eye, hair and skin pigmentation in a dataset of > 6500 individuals from Mexico, Colombia, Peru, Chile and Brazil (including genome-wide SNP data and quantitative/categorical pigmentation phenotypes - the CANDELA dataset CAN). We evaluated accuracy in relation to different analytical methods and various phenotypic predictors. As expected from statistical principles, we observe that quantitative traits are more sensitive to changes in the prediction models than categorical traits. We find that Random Forest or Linear Regression are generally the best performing methods. We also compare the prediction accuracy of SNP sets defined in the CAN dataset (including 56, 101 and 120 SNPs for eye, hair and skin colour prediction, respectively) to the well-established HIrisPlex-S SNP set (including 6, 22 and 36 SNPs for eye, hair and skin colour prediction respectively). When training prediction models on the CAN data, we observe remarkably similar performances for HIrisPlex-S and the larger CAN SNP sets for the prediction of hair (categorical) and eye (both categorical and quantitative), while the CAN sets outperform HIrisPlex-S for quantitative, but not for categorical skin pigmentation prediction. The performance of HIrisPlex-S, when models are trained in a world-wide sample (although consisting of 80% Europeans, https://hirisplex.erasmusmc.nl), is lower relative to training in the CAN data (particularly for hair and skin colour). Altogether, our observations are consistent with common variation of eye and hair colour having a relatively simple genetic architecture, which is well captured by HIrisPlex-S, even in admixed Latin Americans (with partial European ancestry). By contrast, since skin pigmentation is a more polygenic trait, accuracy is more sensitive to prediction SNP set size, although here this effect was only apparent for a quantitative measure of skin pigmentation. Our results support the use of HIrisPlex-S in the prediction of categorical pigmentation traits for forensic purposes in Latin America, while illustrating the impact of training datasets on its accuracy.

A GWAS in Latin Americans identifies novel face shape loci, implicating VPS13B and a Denisovan introgressed region in facial variation.

To characterize the genetic basis of facial features in Latin Americans, we performed a genome-wide association study (GWAS) of more than 6000 individuals using 59 landmark-based measurements from two-dimensional profile photographs and ~9,000,000 genotyped or imputed single-nucleotide polymorphisms. We detected significant association of 32 traits with at least 1 (and up to 6) of 32 different genomic regions, more than doubling the number of robustly associated face morphology loci reported until now (from 11 to 23). These GWAS hits are strongly enriched in regulatory sequences active specifically during craniofacial development. The associated region in 1p12 includes a tract of archaic adaptive introgression, with a Denisovan haplotype common in Native Americans affecting particularly lip thickness. Among the nine previously unidentified face morphology loci we identified is the VPS13B gene region, and we show that variants in this region also affect midfacial morphology in mice.

Genetic components of human pain sensitivity: a protocol for a genome-wide association study of experimental pain in healthy volunteers.

INTRODUCTION: Pain constitutes a major component of the global burden of diseases. Recent studies suggest a strong genetic contribution to pain susceptibility and severity. Whereas most of the available evidence relies on candidate gene association or linkage studies, research on the genetic basis of pain sensitivity using genome-wide association studies (GWAS) is still in its infancy. This protocol describes a proposed GWAS on genetic contributions to baseline pain sensitivity and nociceptive sensitisation in a sample of unrelated healthy individuals of mixed Latin American ancestry. METHODS AND ANALYSIS: A GWAS on genetic contributions to pain sensitivity in the naïve state and following nociceptive sensitisation will be conducted in unrelated healthy individuals of mixed ancestry. Mechanical and thermal pain sensitivity will be evaluated with a battery of quantitative sensory tests evaluating pain thresholds. In addition, variation in mechanical and thermal sensitisation following topical application of mustard oil to the skin will be evaluated. ETHICS AND DISSEMINATION: This study received ethical approval from the University College London research ethics committee (3352/001) and from the bioethics committee of the Odontology Faculty at the University of Antioquia (CONCEPTO 01-2013). Findings will be disseminated to commissioners, clinicians and service users via papers and presentations at international conferences.

A GWAS in Latin Americans highlights the convergent evolution of lighter skin pigmentation in Eurasia.

We report a genome-wide association scan in >6,000 Latin Americans for pigmentation of skin and eyes. We found eighteen signals of association at twelve genomic regions. These include one novel locus for skin pigmentation (in 10q26) and three novel loci for eye pigmentation (in 1q32, 20q13 and 22q12). We demonstrate the presence of multiple independent signals of association in the 11q14 and 15q13 regions (comprising the GRM5/TYR and HERC2/OCA2 genes, respectively) and several epistatic interactions among independently associated alleles. Strongest association with skin pigmentation at 19p13 was observed for an Y182H missense variant (common only in East Asians and Native Americans) in MFSD12, a gene recently associated with skin pigmentation in Africans. We show that the frequency of the derived allele at Y182H is significantly correlated with lower solar radiation intensity in East Asia and infer that MFSD12 was under selection in East Asians, probably after their split from Europeans.

Single-Nucleotide Polymorphisms in NOD1, RIPK2, MICB, PLCE1, TNF, and IKBKE Genes Associated with Symptomatic Dengue in Children from Colombia.

Functional immunological evidence supports the impact that the host genetic variability has on the susceptibility to develop asymptomatic or symptomatic dengue infection. Children are more prone to develop severe dengue. Thus, we have evaluated possible associations between single-nucleotide polymorphisms (SNPs) located in immune genes and the development of symptomatic dengue in children from two Colombian populations with differences in genetic backgrounds and geographical features. We genotyped 15 SNPs (in 12 genes) in 298 symptomatic children and 648 healthy controls. Ancestry proportions (APs) were inferred by genotyping 29 ancestry informative markers. We observed four SNPs associated with susceptibility to develop dengue in NOD1, RIPK2, MICB, or PLCE1 genes. Conversely, we found one SNP in TNF gene and two haplotypes in the IKBKE gene associated with resistance to develop dengue. These associations were adjusted by gender, APs, and the population of origin because the association of polymorphisms may be different in admixed populations like Colombian. To our knowledge, this is the first reported association study with dengue in IKBKE, RIPK2, and NOD1 genes. We have also confirmed previously reported associations in MICB and PLCE1 genes with dengue. Overall, our results contribute to the understanding of the genetic susceptibility/resistance to develop symptomatic dengue. Nevertheless, these associations must be validated through functional analysis.

Latin Americans show wide-spread Converso ancestry and imprint of local Native ancestry on physical appearance.

Historical records and genetic analyses indicate that Latin Americans trace their ancestry mainly to the intermixing (admixture) of Native Americans, Europeans and Sub-Saharan Africans. Using novel haplotype-based methods, here we infer sub-continental ancestry in over 6,500 Latin Americans and evaluate the impact of regional ancestry variation on physical appearance. We find that Native American ancestry components in Latin Americans correspond geographically to the present-day genetic structure of Native groups, and that sources of non-Native ancestry, and admixture timings, match documented migratory flows. We also detect South/East Mediterranean ancestry across Latin America, probably stemming mostly from the clandestine colonial migration of Christian converts of non-European origin (Conversos). Furthermore, we find that ancestry related to highland (Central Andean) versus lowland (Mapuche) Natives is associated with variation in facial features, particularly nose morphology, and detect significant differences in allele frequencies between these groups at loci previously associated with nose morphology in this sample.

Terapias usuales y emergentes en colangitis biliar primaria / Conventional and emerging therapies in primary biliary cholangitis

La colangitis biliar primaria (CBP) es una enfermedad autoinmune caracterizada por daño de los conductos biliares intrahepáticos, que hasta ahora tiene mecanismos poco claros de respuesta celular inflamatoria, con la mitocondria como orgánulo blanco. Durante varias décadas han sido el control de los ácidos biliares y el tratamiento de la colestasis lo que ha permitido el manejo médico de los pacientes, logrando un impacto parcial en el curso y la progresión de la enfermedad, mejorando además la sobrevida de los individuos. Con el hallazgo de nuevos mecanismos fisiopatológicos se han iniciado estudios con terapias inmunomoduladoras, que podrían ser prometedoras en el mejoramiento de la calidad de vida de los pacientes que padecen la enfermedad. Aún los resultados son inciertos, y se hacen necesarios más estudios para aclarar el papel de los nuevos tratamientos en el arsenal terapéutico disponible para la CBP.

Primary biliary cholangitis (PBC) is an autoimmune disease characterized by damage of intrahepatic bile ducts, so far with unclear mechanisms of inflammatory cellular response with the mitochondria as the target organelle. For several decades it has been the control of bile acids and the treatment of cholestasis what has allowed the management of patients, achieving a partial impact on the course and progression of the disease, also improving the survival of individuals. With the discovery of new pathophysiological mechanisms, studies have been initiated with new immunomodulatory therapies that could be promising in improving the quality of life of patients suffering from the disease. The results are still uncertain and further studies are needed to clarify the role of the new treatments in the therapeutic arsenal available for PBC.

Colangitis esclerosante asociada a infección severa por SARS-CoV-2 / Sclerosing cholangitis associated with severe infection by SARS-CoV-2

La colangitis esclerosante secundaria es una enfermedad poco prevalente, de etiología multifactorial y con una fisiopatología progresiva, caracterizada por obstrucción biliar y fibrosis. Entre las múltiples causas se destacan las siguientes: inmunomediada por IgG4, isquémica, infecciosa y relacionada a medicamentos. En el contexto de la pandemia por SARS-CoV-2, se han reportado algunas series de casos que determinan una asociación entre estas dos entidades. Se presenta el caso de una mujer en la octava década de la vida con infección por SARS-CoV-2 grave, que cursó con ictericia progresiva, perfil hepático con patrón colestásico, y hallazgos imagenológicos de colangitis esclerosante con vía biliar desestructurada de manera difusa, microcálculos y barro biliar. Se diagnosticó colangitis esclerosante secundaria a SARS-CoV-2 y se dio manejo con ácido ursodesoxicólico.

Secondary sclerosing cholangitis is a rare disease of multifactorial etiology with a progressive pathophysiology, characterized by biliary obstruction and fibrosis. Multiple causes include: IgG4-immunemediated, ischemic, infectious and drug-induced. In the context of the SARS-CoV-2 pandemic, some case series have been reported that determine an association between these two entities. We present the case of a woman in her eighth decade with severe SARS-CoV-2 infection that presented with progressive jaundice, liver profile with cholestatic pattern, and imaging findings of sclerosing cholangitis with obliterated bile ducts, microlithiasis and biliary sludge. Sclerosing cholangitis secondary to SARS-CoV-2 was diagnosed and the patient was treated with ursodeoxycholic acid.

[Variants in the TNFA, IL6 and IFNG genes are associated with the dengue severity in a sample from Colombian population].

INTRODUCTION: The genetic makeup of the host contributes to the clinical profile of dengue. This could be due to the effect of variants in the genes encoding pro-inflammatory cytokines. OBJECTIVE: To evaluate the association between the variants of three polymorphisms in TNFA, IL6 and IFNG candidate genes with dengue severity in a sample of Colombian population. MATERIALS AND METHODS: We evaluated the rs1800750, rs2069843, and rs2069705 polymorphisms in TNFA, IL6 and IFNG candidate genes, respectively, in 226 patients with dengue infection. The genotypes were typed using both polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP). To determine the risk of different dengue phenotypes, we compared allele frequencies with chi-square and genotypes and haplotypes using logistic regression. Finally, these analyzes were adjusted with data from self-identification or the ancestral genetic component. RESULTS: The A allele in the rs2069843 polymorphism, adjusted by self-identification, was associated with dengue hemorrhagic fever cases in Afro-Colombians. In the entire sample, this polymorphism, adjusted by the ancestral genetic component, was reproducible. In addition, there were significant associations between GGT and GAC allelic combinations of rs1800750, rs2069843, and rs2069705 in dengue hemorrhagic fever patients, with and without adjustment by ancestral genetic component. Additionally, the AGC allelic combination produced 58.03 pg/ml of interleukin-6 more than the GGC combination, regardless of European, Amerindian and African genetic components. CONCLUSIONS: The variants of GGT and GAC polymorphisms of rs1800750, rs2069843, and rs2069705 in the TNFA, IL6 and IFNG genes, respectively, were correlated with the susceptibility to dengue severity in a sample of Colombian population.

Admixture in Latin America.

Latin Americans arguably represent the largest recently admixed populations in the world. This reflects a history of massive settlement by immigrants (mostly Europeans and Africans) and their variable admixture with Natives, starting in 1492. This process resulted in the population of Latin America showing an extensive genetic and phenotypic diversity. Here we review how genetic analyses are being applied to examine the demographic history of this population, including patterns of mating, population structure and ancestry. The admixture history of Latin America, and the resulting extensive diversity of the region, represents a natural experiment offering an advantageous setting for genetic association studies. We review how recent analyses in Latin Americans are contributing to elucidating the genetic architecture of human complex traits.

Disfunción renal en el paciente cirrótico / Renal dysfunction in the cirrhotic patient

La disfunción renal es una complicación común en pacientes con cirrosis avanzada y está asociadaa un incremento significativo en la mortalidad. Este deterioro de la función renal puede ser reversible en algunos casos, si se identifica y se trata su etiología. La lesión renal aguda (LRA) de origen prerrenal y la necrosis tubular aguda (NTA) son las entidades más frecuentes en pacientes con enfermedad hepática crónica y cirrosis, constituyendo un desafío en los escenarios clínicos actuales. La aparición de nuevos biomarcadores como la lipocalina asociada a la gelatinasa de neutrófilos (NGAL), puede ser un factor determinante para esclarecer el origen de estas dos entidades. En la actualidad, la clasificación de la enfermedad renal establece que un aumento en la creatinina sérica basal >0,3 mg/dL dentro de las primeras 48 horas, o un incremento mayor al 50% desde la línea de base, son suficientes para definir lesión renal aguda, por lo cual, cambios leves en la creatinina sérica en un periodo corto de tiempo, contribuyen a una identificación temprana y previenen desenlaces negativos. Esta revisión de tema abordará la lesión renal aguda en cirrosis desde la fisiopatología, la clasificación actual según guías internacionales, los avances en biomarcadores y las principales etiologías, finalizando con un abordaje general y estrategias de prevención.

Kidney dysfunction is a common complication in patients with advanced cirrhosis and is associated with a significant increase in mortality. This deterioration of kidney function may be reversible in some cases, if its etiology is identified and treated. Acute kidney injury (AKI) of prerenal origin and acute tubular necrosis (ATN) are the most frequent entities in patients with chronic liver disease and cirrhosis, constituting a challenge in current clinical scenarios. The emergence of new biomarkers such as neutrophil gelatinase-associated lipocalin (NGAL), may be a determining factor in clarifying the origin of these two entities. Currently, the classification of renal disease establishes that an increase in basal serum creatinine >0,3 mg/dL within the first 48 hours, or an increase higher than 50% from the baseline, are enough to define acute kidney injury, therefore slight changes in serum creatinine in a short period of time contribute to an early identification and prevent negative outcomes. This literature review will address acute kidney injury in cirrhosis from its pathophysiology, current classification according to international guidelines, advances in biomarkers and the main etiologies associated with it, ending with a general approach and prevention strategies.

A genome-wide association scan in admixed Latin Americans identifies loci influencing facial and scalp hair features.

We report a genome-wide association scan in over 6,000 Latin Americans for features of scalp hair (shape, colour, greying, balding) and facial hair (beard thickness, monobrow, eyebrow thickness). We found 18 signals of association reaching genome-wide significance (P values 5 × 10(-8) to 3 × 10(-119)), including 10 novel associations. These include novel loci for scalp hair shape and balding, and the first reported loci for hair greying, monobrow, eyebrow and beard thickness. A newly identified locus influencing hair shape includes a Q30R substitution in the Protease Serine S1 family member 53 (PRSS53). We demonstrate that this enzyme is highly expressed in the hair follicle, especially the inner root sheath, and that the Q30R substitution affects enzyme processing and secretion. The genome regions associated with hair features are enriched for signals of selection, consistent with proposals regarding the evolution of human hair.