People with two X chromosomes could possess multiple cone cell pigments, perhaps born as full tetrachromats who have four simultaneously functioning kinds of cone cell, each type with a specific pattern of responsiveness to different wave-lengths of light in the range of the visible spectrum.[20] One study suggested that 15% of the world's women might have the type of fourth cone whose sensitivity peak is between the standard red and green cones, giving, theoretically, a significant increase in color differentiation.[21] Another study suggests that as many as 50% of women and 8% of men may have four photopigments and corresponding increased chromatic discrimination compared to trichromats.[22] In 2010, after twenty years of study of women with four types of cones (non-functional tetrachromats), neuroscientist Dr. Gabriele Jordan identified a woman (subject cDa29) who could detect a greater variety of colors than trichromats could, corresponding with a functional tetrachromat (or true tetrachromat).[23][24][25][26]