Apes Walking Upright: That's Just How They Roll (or Walk).

Orangutans, gorillas and chimpanzees do it. Bonobos seem to love doing it. Apparently gibbons do it really well. Indeed, bipedalism is not unique to humans and is quite common among apes. Apes are known to walk upright once in awhile, although bonobos seem to do it more frequently than other apes. Bipedalism is just one of the natural repertoire of ape locomotion.

(From left to right) Upright Apes Brigade: Gibbon, Orangutan, Gorilla, Chimpanzee and Bonobo. Click photo for larger image.

Upright Gorilla Goes Viral: 

Ambam the gorilla. Photo from Dailymail.

Currently going viral on the internet is a video of Ambam, a Western lowland gorilla (Gorilla gorilla gorilla) that was filmed walking upright in his enclosure. This 21 year-old, 485 lb. ape currently resides at Port Lympne wild animal park in Kent, England.

If you have not heard of Ambam or caught on to this internet sensation, you can read about him on :
Ambam, the swaggering silverback gorilla who walks around his pen on two legs (DailyMail)
Yes, he can walk. But just how close IS he to being human? (DailyMail)
Walk like a man: Gorilla strolls on hind legs (MSNBC).

It is not uncommon to see a gorilla walk upright but what's unique about Ambam is that he seems to walk upright quite frequently and good at it too. Bipedal locomotion is common in gorillas but they spend most of their time knuckle-walking. Ambam's upright gait and locomotion is definitely not an upright display to intimidate. Instead, it is most probably in response to curiosity and foraging in his enclosure. One of his keeper, Phil Ridges said:

"We think he might use it to get a height advantage to look over the wall when keepers come to feed him and standing up can also help him in looking for food generally in his enclosure as it gives him a better vantage point." Ridges added that Ambam could also carry more food if his hands were freed from walking and it also meant "he doesn't get his hands wet when it is raining."

It seems that the penchant for bipedalism runs deep in Ambam's family. His father, sister and half-sister (same father) prefer to walk upright and stand the same way as Ambam.

Ambam standing upright. Photo from Dailymail.

Is this a novel behavior in response to being in captivity? Is his skeletal and muscular structure (and in some sense his father, sister and half-sister) different than other gorillas? I think it would be interesting to see a behavioral study and an ethogram on Ambam's choice of locomotion. What are the percentage (or time spent) of him walking upright compared to knuckle-walking. Will his offspring be a fan of bipedality as well?

The Other Upright Ape:
While Ambam seem to prefer walking upright once in awhile, there is another ape that came before him who is a habitual biped. This ape is a chimpanzee named Oliver.

Oliver was a media (and science) sensation in the 60s and 70s for his preferred upright locomotion, having 47 chromosomes and a less prognathic face compared to other chimpanzees. Humans have 46 chromosomes while chimpanzees have 48 chromosomes. It was thought that Oliver is a "missing link" between chimpanzees and humans, thus nicknamed the "humanzee". While Oliver is not the missing link (Ely et al.,1998), he is truly a habitual biped.

The 52 year-old Oliver currently resides at Primarily Primates, a sanctuary in San Antonio, Texas. Below is a really good video of Oliver from his early years to his retirement. Seeing what happened to Oliver, I hope that they will not parade Ambam around like a freak of nature.

UPDATE: Oliver passed away on June 2nd 2012 at Primarily Primates. Read more here.

Reference:
Ely, J.J. Leland, M. Martino, M. Swett, W. Moore, C.M. 1998. Technical note: Chromosomal and mtDNA analysis of Oliver. American Journal of Physical Anthropology 105(3) 395-403. DOI: http://www3.interscience.wiley.com/journal/28165/abstract?CRETRY=1&SRETRY=0