Human skin color ranges in variety from the darkest brown to the lightest hues.
Skin is the soft outer tissue covering vertebrates.
The Biology of Skin Color — HHMI BioInteractive Video by biointeractive
An individual's skin pigmentation is the result of genetics, being the product of both of the individual's biological parents' genetic makeup.
A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption.
A gene is a locus of DNA which is made up of nucleotides and is the molecular unit of heredity.
Genetics is the study of genes, genetic variation, and heredity in living organisms.
What Everyone Should Know About Skin Color and "Race" by Think Fact
In evolution, skin pigmentation in human beings evolved by a process of natural selection primarily to regulate the amount of ultraviolet radiation penetrating the skin, controlling its biochemical effects.
Ultraviolet is an electromagnetic radiation with a wavelength from 10 nm to 400 nm, shorter than that of visible light but longer than X-rays.
Natural selection is the differential survival and reproduction of individuals due to differences in phenotype.
The actual skin color of different humans is affected by many substances, although the single most important substance is the pigment melanin.
Melanin is a broad term for a group of natural pigments found in most organisms.
Melanin is produced within the skin in cells called melanocytes and it is the main determinant of the skin color of darker-skinned humans.
Melanocytes are melanin-producing neural-crest derived cells located in the bottom layer of the skin's epidermis, the middle layer of the eye, the inner ear, meninges, bones, and heart.
The skin color of people with light skin is determined mainly by the bluish-white connective tissue under the dermis and by the hemoglobin circulating in the veins of the dermis.
The dermis or corium is a layer of skin between the epidermis and subcutaneous tissues, that primarily consists of dense irregular connective tissue and cushions the body from stress and strain.
Hemoglobin or Haemoglobin ; abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein in the red blood cells of all vertebrates as well as the tissues of some invertebrates.
Light skin is a naturally occurring human skin color, which has little eumelanin pigmentation and which has been adapted to environments of low UV radiation.
The red color underlying the skin becomes more visible, especially in the face, when, as consequence of physical exercise or the stimulation of the nervous system, arterioles dilate.
An arteriole is a small-diameter blood vessel in the microcirculation that extends and branches out from an artery and leads to capillaries.
The nervous system is the part of an animal that coordinates its actions by transmitting signals to and from different parts of its body.
Physical exercise is any bodily activity that enhances or maintains physical fitness and overall health and wellness.
Color is not entirely uniform across an individual's skin; for example, the skin of the palm and the sole is lighter than most other skin, and this is especially noticeable in darker-skinned people.
There is a direct correlation between the geographic distribution of UV radiation and the distribution of indigenous skin pigmentation around the world.
Areas that receive higher amounts of UVR, generally located closer to the equator, tend to have darker-skinned populations.
Areas that are far from the tropics and closer to the poles have lower intensity of UVR, which is reflected in lighter-skinned populations.
Researchers suggest that human populations over the past 50,000 years have changed from dark-skinned to light-skinned and vice versa as they migrated to different UV zones, and that such major changes in pigmentation may have happened in as little as 100 generations through selective sweeps.
In genetics, a selective sweep is the reduction or elimination of variation among the nucleotides near a mutation in DNA.
Natural skin color can also darken as a result of tanning due to exposure to sunlight.
Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light.
The leading theory is that skin color adapts to intense sunlight irradiation to provide partial protection against the ultraviolet fraction that produces damage and thus mutations in the DNA of the skin cells.
Deoxyribonucleic acid is a molecule that carries the genetic instructions used in the growth, development, functioning and reproduction of all known living organisms and many viruses.
In addition, it has been observed that adult human females on average are significantly lighter in skin pigmentation than males.
Females need more calcium during pregnancy and lactation.
Lactation describes the secretion of milk from the mammary glands and the period of time that a mother lactates to feed her young.
Pregnancy, also known as gravidity or gestation, is the time during which one or more offspring develops inside a woman.
Calcium is a chemical element with symbol Ca and atomic number 20.
The body synthesizes vitamin D from sunlight, which helps it absorb calcium.
Vitamin D refers to a group of fat-soluble secosteroids responsible for increasing intestinal absorption of calcium, magnesium, phosphate, and zinc.
Females evolved to have lighter skin so their bodies absorb more calcium.
The social significance of differences in skin color has varied across cultures and over time, as demonstrated with regard to social status and discrimination.
In human social affairs, discrimination is treatment or consideration of, or making a distinction in favor of or against, a person or thing based on the group, class, or category to which that person or thing is perceived to belong to rather than on individual merit.
Social status is the position or rank of a person or group, within the society.