6.1 Digestion & Absorption 6.2 Blood System 6.3 Defense Against Infectious Disease 6.4 Gas Exchange 6.5 Neurons & Synapses 6.6 Hormones, Homeostasis & Reproduction
"The Evolution of Lactose Tolerance" by BioInteractive (15:04)
This video examines the possible reasons why some humans have retained the
ability to digest lactose beyond infancy (which is not normal amongst mammals).