Ape years ago (Mya) the clades diverged into newer clades. The lesser apes are the gibbon family, Hylobatidae, of sixteen species; all are native to Asia. Their major differentiating characteristic is their long arms, which they use to brachiate through trees. Their wrists are ball and socket joints as an evolutionary adaptation to their arboreal lifestyle. Generally smaller than the African apes, the largest gibbon, the siamang, weighs up to ; in comparison, the smallest "great ape", the bonobo, is . Formerly, all the great apes except humans were classified as the family Pongidae, which conveniently provided for separating the human
Ape index who all had significantly higher Ape Indices than those found in the control group. Thus they left open the possibility that the Ape Index may be more significant when there is a greater degree of equivalence between the other traits under consideration. Countering these studies are other works that have identified the Ape Index as a significant (or potentially significant) factor. A 2001 study comparing teenage male and female rock climbers noted that performance differences between the genders could be explained by a number of factors, one of which was the lower Ape Index found in the female climbers. Similarly,