Small human body size, or the “pygmy” phenotype, is strongly associated with populations who have traditionally hunted and gathered for food in tropical rainforest habitats. The phenotype appears to have evolved independently at least twice: in both Central Africa and Southeast Asia. The likely convergence has led anthropologists to hypothesize that small body size may confer direct or indirect fitness benefits in response to one or more common ecological challenges of the tropical rainforest: (i) food limitation, (ii) high heat and humidity, (iii) forest structural density, (iv) high pathogen load, or (v) high adult mortality. To study the evolutionary ecology of the pygmy phenotype and rainforest hunter-gatherers in general, with my colleagues Nate Dominy and Luis Barreiro, I have worked closely with the Batwa, who traditionally hunted and gathered for food in Bwindi Impenetrable Forest (southwest Uganda) before it was gazetted as a National Park in 1992. I will describe results from genomic studies designed to confirm the genetic basis of the pygmy phenotype, identify genetic regions associated with the phenotype, and indirectly examine the evolutionary history of the phenotype through the study of those regions. I will also present preliminary results from ecological experiments designed to assess the plausibility of various ecological hypotheses for the adaptive origins of the pygmy phenotype.