Sexual Dimorphism

       Sexual dimorphism is a term which means the difference between the male and female of a species. In a previous blog (http://anthropologicalconcepts.weebly.com/blog/male-or-female) I discussed how the skeleton of male and female differentiate, which is a form of sexual dimorphism, but a very small percentage of it (about 1%). In humans male and female also differ slightly in physical appearance; from amount of hair to amount of musculature. But what of other hominids? In the following blog I will discuss the difference between male and female non-human primates. I first want to speak of those whose sexual dimorphism is evident, then to those with whom it is not so evident.
​       Our first non-human ape is the orangutan. This is an ape who inhabits Borneo, Malaysia, and Sumatra, Indonesia, and whose method of locomotion is sometimes travel on the ground, but their more common locomotion is brachiation (climbing trees) so both males and females have arms longer than their torsos. Aside from the arms and the colour of their hair (orange), they could not be more different. The male orangutan has body mass more than twice than that of females, and with that they are also larger and heavier. They also have larger canines and first lower premolars (refer to: http://anthropologicalconcepts.weebly.com/blog/-diet-and-teeth). But even though these are all immediately evident that the larger ones are males, but there is one element that removes all doubt. This element are the large cheek pads; only male orangutans have these (image below). Something that helps in this huge difference is when the female hits adulthood, they stop growing, while the male still grows. That said, when orangutans are babies, it is difficult to tell apart the males and females. 

       With orangutans they do not have an alpha male, unlike the next ape I will address; the gorilla. This ape lives either in a small section of lowlands or of mountains of Africa; the latter being lowland gorillas and former being mountain gorillas. Unlike the orangutans who spend little time on the ground, gorillas spend much time on the ground. That said, their method of locomotion is that of quadrupedal knuckle walkers. In the community of the gorilla, there is one alpha male, known as a silverback, a few females, and their offspring. Their packs consist of about 10 individuals. In contrast to the male orangutans, male gorillas do not have cheek pads, but the sexual dimorphism in them is just as noticeable. Female gorillas generally weigh between 154 lb (70 kg) or 198 lb (90kg), while male gorillas come in at 440 lb (200 kg) (image below for comparison). 

       We now switch to apes whose sexual dimorphism is not as great as the two I have just addressed. The first I will speak of might as well be a cousin to us humans, which is the chimpanzee. Even though their form of locomotion is quadrupedal knuckle walkers like the gorillas, they also comfortably climb trees. Chimpanzees live in tropical forests and bordering savannas. And unlike the gorillas they do not several female partners, they form monogamous mating bonds in a community numbering from 10 to 50 individuals. Humans and chimpanzees do not differ much, and sexual dimorphism is one of things we have in common with them. I am not saying that we have the same sexual dimorphism but we have small differences between our males and females. The average weight for a male chimpanzee is 88.2 to 132 lb (40 to 60 kg) and for the average female chimpanzee is 70.5 to 104 lb (32 to 47 kg), which is nowhere near the difference between male and female gorillas. As for the size both female and male chimpanzees tend to be about the same height, but the females are less muscular, like humans. 

       The last ape I will speak of are the gibbons. These apes inhabit southeast Asia. Like the orangutans, gibbons also use brachiation as a form of locomotion, but unlike the orangutans, they are much smaller and slender, so they are able to walk bipedally on top of branches. These apes, like the chimpanzees, are monogamous (this includes forming a nuclear family which is two mated adults with their juvenile offspring). Now, unlike the three apes I have spoken of, which are classified as part of the “great apes,”gibbons fall under the classification of “lesser apes” (or “smaller apes). At the average height for all gibbons, male and female, being at 3 ft, this is understandable. Just like the chimpanzees the sexual dimorphism is not great; if anything it is less than that of the chimpanzees. The average male gibbon weights 12.3 lb (5.6 kg) and the average female weights 12.7 lb (5.8 kg). So both male and female gibbons weight pretty much the same. Now there is a species of gibbons known as siamangs, which hold the biggest male gibbons weighing between 15 lb (7 kg) and 30 lb (13.5 kg).

       It is amazing how much apes vary, from human to gorilla. Brachiation is a rare ability for primates (only a few New World monkey species have that as well). As for the quadrupedal knuckle walking, only the chimpanzees and gorillas have shown this skill. But the form of locomotion is probably all the chimpanzees and gorillas share in common; along with the orangutans and gibbons, the only thing they share in common is brachiation. What is more, of the apes I have addressed in this blog, one is the biggest ape species (gorillas), along with the smallest (gibbons). But that said, we are all family, we are all apes.
​       Please feel free to comment on what you thought of the blog, or other physical anthropological subjects you would like me to cover.
                                                                 (from left to right: human, gorilla, chimpanzee, orangutan, gibbon)