Select Human Trait and Hypothesize its Evolution

Human features, often known as characteristics, include everything that controls people’s behavior when they exercise free will. A person’s personality is made up of traits, some of which are passed down from parents. Humans have a variety of characteristics, including a cleft chin, a tongue roll, facial dimples, a free earlobe, and different eye colors. Melanin is the main pigment responsible for affecting the variances in eye color. More melanin intensifies the color (PRIME, 2012). The melanin-producing alleles are predominate in people with colored eyes. Is there a hereditary component to eye color?
Charles Darwin’s sexual selection theory is one explanation that explains how humans acquired their unique eye color feature. Darwin proposed in 1871 that human sex differences evolved based on sexual selection. When there is competition between multiple women over scarce men, the choice of perceptible female characters hyper arouses particular processes in the male brain, specifically those for femininity appreciation and fertility valuation. Human beings can choose their mates based on specific appealing characteristics, an example being the eye color. To some individuals, a particular eye shade is more alluring. Thus, they choose a partner with that specific color. At the end, when the two link sexually, those genes are conveyed to their progenies, and they continue to exist in the gene pool (MIZZOU WEEKLY, 2012). Another theory by Rodrigues and Young indicate that variations in human eye color are maintained by Negative Frequency-Dependent selection. Human commercial models in two populations; UK and Brazil were used, and eye color frequencies were inverted. Blue eyes are dominant in the United Kingdom whereas, in Brazil, brown eyes are overriding. For both genders in the two nations, rarer eye pigment was more frequent in commercial model populations than the general inhabitants. Findings proved that miscellany in humans is upheld by adverse frequency-dependent selection and the variance was more profound in females than male models (Young, 2016). Thomas Hunt’s Chromosome Theory of Heredity, states that inheritance arrays may be elucidated by supposing that genes are positioned in exact locations of chromosomes. He used fruit flies to carry out his experiment, and after mating a red-eyed female with a white-eyed male, the product was a red-eyed progeny. From this result, Hunt established that the allele- manufacturing eye pigment must lie on the X chromosome that manages sex. Sex-linkage are on the sex chromosomes; X and Y, and females have two replicas of each, whereas males have one (Genoma, 2016).

Evolution of the Eye Color

The original human descendants are alleged to have come from Africa. Present day mortal beings appeared when primates adapted and branched off into various species in the tree of life. Due to direct sunlight and the warm temperatures with the cutting of the equator immediate through Africa, the natural selection of dark skin color is evident. The nuclear gene that controls eye color is closely linked to the one controlling skin color. Prehistoric ancestors are believed to have had nearly black or dark brown eyes and very dark hair. Brown eyes are considered domineering, however, currently, there are many different eye colors. Scientists consent that natural selection for the brighter eye pigment is connected to the reduction of collection for the dimmer skin tones. With the relocation of human beings around the globe, the burden for selection of dark skin color lessened. Those who settled in Western Europe were no longer compelled to select dark skin and eyes for existence. Higher latitudes away from Africa gave different seasons therefore with lack of pressure for selection; genes were expected to transform.

The eye color is a polygenic trait; not dictated by a single gene like other traits. Multiple dissimilar DNAs on several chromosomes carry info concerning the eye color an individual should have. When expressed, these genes blend to create numerous shades of assorted colors. Relaxed selection for murky color permitted more mutations to occur. .More alleles were thus generated to join in the gene pool and make ranging eye colors. Individuals with Western European ancestry have lighter eye shades than those from other parts of the world. Parts of this DNA form such individuals is similar to Neanderthal man, who had lighter hair and eye color than the Homo Sapien (Scoville, 2017).

An individual’s eye color results from the coloration of a structure known as the iris which environs the pupil. It aids in regulating the quantity of light inflowing the eye. Variations in a person’s genes determine the pigmentation of the eye. Most of these genes are involved in the storage and transportation of a pigment known as melanin. The amount and quality of melanin in the front layers of the iris relates to the color. Individuals with brown eyes have a tremendous amount of melanin in the iris than those with less. A particular gene in chromosome 15 plays a crucial role in eye color. Two genes, OCA2 and HERC2, are situated tightly together, and the former mature melanosomes, cellular structures that manufacture and keep melanin. Common variations in this gene lower the amount of functional P protein produced thus less melanin is extant in the iris, causing blue eyes instead of brown, in beings with a polymorphism in this gene. Other genes that combine with OCA2 and HERC2 to produce a continuum of eye colors include; ASIP, SLC24A2, TPCN2, TYR, IRF4, AND TYRP1.

Research shows that the passing on of eye color is quite intricate. Eye color in humans was lengthily deliberated as a simple Mendelian trait with the blue eye color allele being controlled by the brown eye color allele. Some people, however, have neither blue nor brown shades, and the color may appear hazel or green from afar. The discrepancy in these colors can be explained genetically by a single-nucleotide, polymorphism (SNP), rs1291382: A>G in the HECT domain and RCC1-like domain 2 (HERC; OMIM #605837) gene (Eiberg et al.2008; Sturm et al.2008). Dominant assumption shows brown eye color is an outcome in individuals with genotype rs12913832; AA or rs12913832; GA. Other alternates situated in one of the exons or the promoter area of OCA2, were initially proposed to impact eye colors. It was postulated that the derived allele of the nonsynonimous mutation rs1800407; A (p.419gln) in OCA2, decreased the pigmentation level of the iris when found in cis phase with rs2913832; A (Anderson et al.2013). Additionally, a minute upsurge in the prediction accuracy of common eye colors was observed by considering rs1129038; G>A, that is in high linkage disequilibrium with rs1291382; A>G in HERC2 (Ruiz ET AL.2013). With the present accord of three eye color groupings, (intermediate, brown and blue), it may be hard to get new indicators for eye color due to color distinction within each group. Individuals also identify eye colors dissimilarly. Skilled stated classification encompasses a sizeable independent component of the single evaluation.

A study was done to investigate the genomic region encompassing the gene OCA2 (NM_000272) and its developer (hg19, chr15; 28,000,023-28,500,021) relative to quantitatively measured eye colors. A sample size of 47 was sequenced using substantial corresponding sequencing. 35 samples of the 47 did not follow the dominant hypothesis based on the genotype of rs12913832; A>G. Samples constituted; subjects with light eye pigmentation and the genotype rs12913832; GG. Eight chosen alternatives were genotyped in additional studies of 515 Scandinavian testers and two southern European inhabitants including; 263 Portuguese and 217 Italians.

Materials and Methods

Moral Acquiescence

The Danish Ethical committee permitted the research and partakers signed well-versed assent.

Individuals and DNA purification.

Blood samples from 263 unrelated Portuguese persons were collected at CESPU University and the University of Porto. Additionally, 217 Italian and 562 Scandinavian samples were used (Pietroni et al.2014; Andersen et al.2013). DNA was purified from blood on FTA cards using BioRobot Workstation in Netherlands and Qiagen.

Digital Photographs and quantitative eye color

Photos were captured close to 10cm in “Raw” setup with a standard EOS Mark V with ISO 800, shutter 1/1000 and AV 18 using a Canon EF 100 mm f/2.8 L IS USM Macro lens with physical concentration. For each single eye snapshot, the eye color was resolute quantitatively.

Quantitative measurement of skin color

Quantitative skin color capacities were executed, using UV-Optimize Scientific 555 (Chromo Light APS) (Kongshoj et al.2006). In use was the pigment protection factor (PPF) as a measure of skin color. Quantities were executed in triplicates on the buttock for each sample and the areas quantified were minus tattoos, hair, nevi, and patches.

Sequencing of the OCA2-HERC2 region

Agilent Technologies, Santa Clara, CA, was used to design capture probes for a 500 kbp region on chromosome 15(hg19, chr15: 28,000,023-28,500,021) for the Halopex Target Enrichment kit with a reading interval of 150 bp.

Analyses of sequence data

Illumina adapters were trimmed using Flexbar (Dodt et al. 2012), and variants were accepted if they had a minimum coverage of 25. Heterozygote variant calls were indorsed if the read occurrence of negligible alternative was >0.15. Established options were investigated using Alamut Batch.

Variant typing and statistical analyses

There were eight deviations in total and numerical calculations were conducted in R ver. 3.0.1. Haplotypes were projected using PHASE ver. 2.1 (Stephen et al. 2001), with standard situations.


In the assortment of individuals for sequencing, a total of 47 testers were chosen for arrangement from an eye color catalog with digital eye imageries of more than 600 people of Scandinavian origin. All the selected individuals were genotyped for HERC2: 12913832: A>G. 35 individuals of Scandinavian descent did not follow the conventional supposition dogged by rs2913832: A>G and 12 personalities followed the leading eye color theory. These were regarded as controls, and they included two persons of type rs12913832: GA with brown eyes, five typed rs12913832: AA with brown eyes as well and rs12913832: GG with blue eyes. Drive of the sequencing investigation was to display new variants that might elucidate the difference in human eye color. Eye color of 35 individuals was not by the hypothesis of a dominant genetic eye color model determined by rs12913832: A>G. 27 had the rs12913832: GA genotype and light eye coloration. Variant alleles were found in the multifaceted heterozygous state with other metamorphoses in two Northern European individuals (Jeppe D. Andersen, 2016).


Human eye color is determined by genetics. Genetic variations sometimes give unexpected outcomes whereby, a child’s eye color might not be similar to those of the parents. Multiple disorders tamper with the eye tinge. Ocular albinism, characterized by sternly condensed pigmentation of the iris, causing real light colored eyes and significant issues with vision. Another condition is referred to as oculocutaneous albinism, which affects the tint eyes as well as the hair and skin. Individuals affected by this tend to have very light-colored irises, white or light-colored hair and fair skin. Both disorders are a result of alterations in genes liable for fabrication and storage of melanin. Heterochromia is another illness that emerges due to genetic changes or an issue during eye development or an infection to the eye.


Genoma. (2016, MARCH 8). Thomas Hunt Morgan and the Chromosome Theory of Heredity. Retrieved from

Jeppe D. Andersen, C. P. (2016). Importance of nonsynonymous OCA2 variants in human eye color prediction. Molecular Genetics and Genomic Medicine, 430.

Mizzou Weekly. (2012, APRIL 22). Darwin’s sexual selection theory best explanation for gender differences. Retrieved from

Prime. (2012, May 1). Human Traits. Retrieved from

Scoville, H. (2017, APRIL 05). The Evolution of Eye Color . Retrieved from

Young, I. R. (2016). Human Commercial Models’ Eye Colour Shows Negative Frequency-Dependent Selection. PLOS.

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