Why some women can see more colors than others

A biological camera

Every organism’s eyesight begins when light enters the eye through the cornea, passes through the pupil, and is focused by the lens onto the retina at the back of the eye. The retina contains photoreceptor cells that convert this light into electrical signals, which are then sent to the brain via the optic nerve for interpretation.

Photoreceptors

Inside the retina are two main types of photoreceptor cells: rods and cones. Rods handle low-light (night) vision and detect brightness, but not color. On the other hand, cones function in brighter light and are responsible for detecting color. These cones are essential to color perception.

Color vision

Humans normally have three types of cones: S-cones (short-wavelength, blue), M-cones (medium-wavelength, green), and L-cones (long-wavelength, red). Each type responds to different parts of the light spectrum, and the brain combines signals from these cones to produce the experience of color.

Seeing colors differently

Variation in cone distribution, density, and sensitivity can lead to subtle differences in color perception. Some people may have a genetic variation that causes color blindness, while others may see a plethora of colors that average people cannot.

A rare superpower

Tetrachromacy is a rare visual phenomenon where an organism has four distinct types of cone cells in its eyes, which enables it to see a broader spectrum of colors compared to the more common trichromatic vision found in humans.

Tetrachromatic potential

While most people are trichromats, some women may carry a fourth photopigment gene due to variations in their X chromosome. This genetic variation opens the door to the rare possibility for humans to have tetrachromacy.

A world bursting with color

On average, humans can see a million to several million different colors, but those who have tetrachromacy can see hundreds of times this amount. Everything around them is far more vivid and extraordinary.

A rare gift

Scientists have only recently come to acknowledge the possibility that this genetic variation might be seen in humans. The rare ability isn’t well understood, but researchers are testing ways in which people might exhibit it.

An ancestral gift

The common ancestor of all vertebrates in the world likely possessed tetrachromatic vision millions of years ago. But as mammals evolved, they lost the biological part of their eyes that allowed them to see colors in four dimensions.

Processing extra color

Since tetrachromacy isn’t just about the eye and actually requires the brain to process the input from four cones separately, some people may have four cone types but remain nonfunctional tetrachromats since they don’t have the corresponding neural circuitry.

The X-factor

Cone opsin genes, which are the photopigments found in the cells of an eye’s retina, are located on the X chromosome. Since women have two X chromosomes, they are more likely than men to inherit a variation that enables a fourth type of cone receptor in the eye.

The puzzle of proving perception

Testing tetrachromacy in humans is difficult because color perception is subjective. It requires individuals to distinguish between hues that appear identical to trichromats. The process of testing often uses highly controlled laboratory lighting and custom visual tests.

Technological tools

Advanced imaging and genetic sequencing have enhanced the ability for scientists to study potential tetrachromats. These tools allow them to look for structural differences in the retina and analyze how cone cells respond to light.

All about art

Some individuals identified as possible tetrachromats have reported seeing nuances in paint and textiles undetectable to others. Artists with this condition may unconsciously use or detect colors outside the normal human spectrum.

Nature meets nurture

Environmental exposure plays a role in developing full tetrachromacy. Without color-rich environments or stimuli, even people with four cones might not refine their ability to use all four channels effectively.

Primates

Some primates (including humans) have evolved to regain a third cone cell that was once lost to our ancestors, which allows us to now view the world in trichromatic vision. This adaptation is thought to improve the ability to distinguish ripe fruits and young leaves, which is crucial for survival.

A fishy realm

Many fish also exhibit tetrachromacy, with their cones tuned to detect subtle differences in the aquatic light spectrum. This helps them identify prey, predators, and mates even in the murky depths of oceans and rivers.

Insects and ultraviolet marvels

Though not the focus of vertebrate-based tetrachromacy, many insects exhibit complex vision systems. Bees, for instance, can detect ultraviolet patterns on flowers, which are seen as landing guides invisible to the human eye.