Today, about one-tenth of the world’s population are southpaws. Why are such a small proportion of people left-handed -- and why does the trait exist in the first place? Daniel M. Abrams investigates how the uneven ratio of lefties and righties gives insight into a balance between competitive and cooperative pressures on human evolution. View Full Lesson/Credits • Eco-friendly, high-quality, minimal waste • Unisex • 100% ring-spun cotton (heather colors contain polyester) • Baby-knit jersey • Shoulder-to-shoulder taping • Cover stitched and hemmed sleeves • Side-seamed