The Directional Asymmetry Of Macaca Mulatto’s Limb Bones And The Second Metacarpal

There is much debate on the existence of population-level laterality andhandness as human being in macaca mulatta. The directional asymmetry is oneof the effective methods for functional laterality of animal’s behaviors.Thepresence or absence of functional laterality in nonhuman primates may shedlight on the origins of human handedness and on the evolution of cerebralasymmetry. There are many researches on the bones’ DA of human beings, butfew of them are on the nonhuman primates. And the data of macaca mulattabones are even rarer. This research investigates the bones’ DA patterns ofmacaca mulatta(the upper limbs, the lower limbs and the second metacarpal)which distribute in the Taihang mountain of north China and probe into therelationship of the DA patterns between the long bones of different limbs.Finally, we analyze the impact of gender and age to DA patterns. We select56pairs of humeri,48pairs of ulnas,51pairs of radius,58pairs of fenuri,56pairsof tibias,49pairs of fibulas and31pairs of the second metacarpal. We measurethe length, transverse diameter, tagittal diameter of each bone. According to thedata, we calculate the DA values of each pair of bones. We conduct all thestatistical analyses with the software of SPSS20.0. All the data have beenanalyzed with descriptive statistics, normal distribution tests, bivariatecorrelation analysis, ANOVA and the Mann-Whitney tests.The main findings and analyses:(1) As a whole, there is left-side advantage in the long bones (humeri, ulnas, and radius) of macaca mulatta and the DAvalues of many variables show significant differences(P<0.05); the right side ofthe second metacarpal is more hairchested and the significant difference exitsamong some of the variables(P<0.05). For most variables of femui, the DAvalues show no significant difference（P>0.05）and few variables have thetendency of right-sidedness. We speculate that the macaca mulatta may havelaterality in behaviors. The macaca mulatta use the right hands more often incatching, holding, climbing and skipping etc. The left upper limb is used insupporting the whole body. And the long bones of lower limbs are used forkeeping balance and coordinating movements. It shows us that there is acomplementary relationship of controlling strength, coordinating movementsand using hands correctly among the long bones.(2) For the macaca mulatta’slimb bones, the difference of DA exits in the different genders. It reminders usthat there is difference between the male and female macaca mulatta lateralitybehaviors. It is related with the social division of labor in their groups.(3) Thedifference of limb bones’ DA also exits in the different ages of macaca mulatta.This point indicates that the asymmetry of macaca mulatta is affected by theirlaterality behaviors, rather than the inheritance controlling.(4) There is certaincorrelation between the same limb bone’s directional asymmetry and the directratio exits in the DAs of most variables. It accounts for that most variables havethe same direction.(5) There are some correlations among different limb bones’DAs of the macaca mulatta and most of them belong to the symmetry of same side. Therefore, we receive some results from the present research. Though someof them are hard to explain, they are interesting and enlightening.