A person with darker skin produces more melanin. Those are the dark brown pigments that come from your skin, hair, or eye color.
Hope that helps. -UF aka Nadia
C. The Bering Land Bridge once connected what would be Russia and North America but the the movement of these continents separated the land bridge
Valves ensure blood flows toward your heart. Vein valves work to bring the blood that flowed down via arteries back up to your heart.
