Taking a Close Look at the Little People: Is the Small Brain of Flores Hominid LB1 a Result of Island Dwarfism?

Abstract

The type specimen (LB1) of the Flores hominid, identified as Homo floresiensis, had a strikingly small cranial capacity — just 400 cc. This tiny brain is quite aberrant compared with all other hominids because LB1 is only 18,000 years old. The grapefruit‐sized brain of LB1 has been attributed to island dwarfism. However, only limited reduction in brain size usually accompanies evolutionary reduction in body size in mammals. Two potential exceptions are the bovid Myotragus on Majorca and small‐bodied hippopotamuses on Madagascar. Both reportedly have smaller brain sizes than expected. But exceptionally small brain size is not universal in island‐living mammals. Candiacervus — the smallest deer on Crete — does not have an unusually small brain; nor does Homo erectus on Java. Although there is evidence that island‐living primates do tend to show smaller body sizes than mainland counterparts, associated effects on brain size have not been studied to date. To fill this gap, we are currently conducting a quantitative study of cranial capacity and body size in a large sample of long‐tailed macaques (Macaca fascicularis). This species is very widespread across South‐East Asia, including Flores, and will permit a test of the hypothesis that brain size is reduced on islands.