IDark Hair Is the Common Case

Look at the human population as a whole and one fact dominates. The large majority of people alive today have black or dark brown hair. It is the prevailing color across Africa, East and South Asia, the Americas and Oceania, and it is common across much of southern and eastern Europe as well.

That is consistent with where the species began. Modern humans arose in Africa, and the ancestral state of human hair is generally inferred to have been dark, rich in eumelanin, the brown to black pigment. The lighter shades that draw so much attention are, in genetic terms, comparatively recent and geographically limited.

Dark hair is also less uniform than the word suggests. Within black and dark brown lies wide variation in the density of eumelanin, in how light catches the strand, and in thickness and curl. The eye collapses all of it into two or three words. The underlying biology does not.

With that held in mind, the interesting question is not why most hair is dark. It is where the exceptions arose, and how.

IIBlond, Twice

Blond hair is most common in northern Europe, around the Baltic and across Scandinavia and Finland, and becomes rarer moving south and east. For a long time it was assumed to have a single origin there. Two studies from Stanford University complicated that picture.

The first, published in 2014, identified one of the switches behind European blond hair. A single-letter change in a stretch of DNA that regulates a gene called KITLG reduced the gene's activity by roughly a fifth in laboratory tests. When the researchers introduced the same change into mice, their coats grew measurably lighter. The gene itself was untouched; only its volume had been turned down.

The second, published in 2012, looked to the other side of the world. Blond hair is common among Indigenous Solomon Islanders, particularly children, and had often been attributed to European contact. Genetic sampling of more than 1,000 islanders told a different story. The blond hair traced to a variant in TYRP1, a gene involved in eumelanin production, that was common across the islands and absent from the European genomes the team examined.

Blond, in other words, arose at least twice, through different genes, in populations with no shared history of the trait. Blond hair in childhood is also observed in some Aboriginal Australian communities of the central and western deserts, a pattern whose genetics remain less studied.

IIIRed, From More Than One Root

Red hair is the rarest of the major shades worldwide, and its highest recorded frequencies are in Scotland and Ireland, with notable concentrations elsewhere in northwestern Europe. It also appears at low frequency in many populations well beyond Europe.

Most red hair traces to several different variants of a single gene, MC1R, which encodes a receptor that tilts pigment production between the darker eumelanin and the red to yellow pheomelanin. How that receptor works is set out in the plain guide to hair pigment. Because red hair generally requires two variant copies, many more people carry a variant than show the trait, which is part of why it can reappear in families after skipping generations.

The deeper surprise came from ancient DNA. A 2007 study led from the University of Barcelona recovered MC1R sequences from two Neanderthals and reported a variant that, when tested in cells, reduced the receptor's activity in a way similar to the variants behind modern red hair. The researchers suggested that some Neanderthals may have had red hair. Their variant was absent from the modern human samples examined, so if red hair did occur among Neanderthals, it arose independently.

Red, like blond, does not trace to a single change. It is a recurring outcome of the same pigment pathway being adjusted in different ways, in different lineages.

IVColor and Structure Travel Separately

Color is only one dimension of hair. Thickness and curl vary across populations too, and they are governed largely by different genes, which is why they combine in so many ways.

Thickness offers the clearest example. A 2013 study from Harvard University and Fudan University examined a variant of the EDAR gene that is common in East Asian and Indigenous American populations and rare elsewhere. The variant was associated with thicker hair shafts in people, and mice engineered to carry it grew thicker hair as well. It is not a pigment gene. It shapes the strand that the pigment sits in.

Curl is shaped largely by the follicle itself. A follicle that is round in cross section and straight in its path tends to produce straight hair; one that is oval and curved produces a curved strand, and the tighter the curve, the tighter the coil. Tightly coiled hair is most common among people of African ancestry, and some researchers have proposed that it may be among the oldest hair forms in the human lineage.

The result is a set of traits that travel separately. Dark, straight and thick; dark and tightly coiled; light and fine; red and wavy. Each combination is a different draw from genes that are inherited largely independently.

VWhy the Map Looks the Way It Does

No single explanation accounts for the distribution of hair color, and researchers regard the leading ideas as hypotheses rather than settled answers.

The first concerns shared genes. Skin pigmentation tracks the intensity of ultraviolet light across latitudes, and several genes that shape skin color, MC1R among them, also shape hair color. On this reading, lighter hair in northern Europe may have arisen partly alongside lighter skin rather than for any reason of its own.

The second is chance. In small or isolated populations, a variant can become common simply through the random arithmetic of inheritance, a process called genetic drift, or because the founders of a population happened to carry it. The Solomon Islands variant has been discussed in these terms. A third idea, that preferences in partner choice favored rarer shades, has been proposed but is difficult to test and remains contested.

Ancient DNA has added a sense of timing. A 2018 genetic analysis led by researchers in London, of a roughly 10,000 year old skeleton found at Cheddar Gorge in England, pointed to dark hair and light eyes. One individual cannot describe a population, but the finding fits a broader pattern in ancient DNA research suggesting that lighter pigmentation became common in northwestern Europe comparatively recently. Studies described here were conducted independently and did not involve any Codeage product.

VIThe Same Map Within One Life

Hair color varies across a single lifetime as well as across the world. Children of European ancestry who are blond in early childhood commonly darken through the school years and adolescence, as eumelanin production in the follicle rises. The genes have not changed. What the follicle is asked to make has.

Sunlight then works on the strand from outside, oxidizing melanin and lightening the oldest lengths of hair. Long hair often carries a gradient from root to tip that records seasons as faithfully as any map records geography.

And eventually, in every population on earth, the same thing happens. Follicles begin producing hair without pigment, and the differences of a lifetime begin to converge on silver. The timing differs between populations, as set out in why hair turns gray, but the direction is shared.

Seen this way, hair color is one of the few traits in which ancestry, a single life and the passage of time are all visible at once.

VIIWhere This Fits

Hair is a structural material, built from keratin and anchored in tissue that renews in cycles across a lifetime, which is why its variation across the world belongs in the Codeage library beside the biology of keratin. It sits within Structural Integrity, the second pillar of The Longevity Code. A pillar names a location in a framework. It describes a category, not an outcome for any reader.

One distinction bears stating plainly. The genetics described here concern ancestry and inheritance. They do not describe any dietary ingredient changing the color of hair, and Codeage does not present any formula as acting on it.

What the research offers instead is perspective. The shades people notice most are, biologically, small adjustments to one shared system, and the differences between them are a record of where people came from rather than a ranking of anything.