Chimpanzees

Anatomy

Chimpanzees are well-known for their strength and ability to walk upright on two feet or bipedally for short distances. They are human's closest living relatives, sharing more than98% of the same DNA and [Page 501]with similarities in immune functions and blood composition. Human and chimpanzee lineages separated about 6 million years ago. We are also their closest relatives of all of the living primates, except bonobos. This means that they can contract any infectious disease that a human can be infected by and has led to exploitation by biomedical research institutions. Bonobos and chimpanzees are thought to have shared a common ancestor from whom they split approximately 3million years ago. Chimpanzees diverged from gorillas 7.5 million years ago and orangutans 16 million years ago.

Chimpanzees live in a variety of habitats, from densely forested jungles to savannas that are believed to closely resemble the environment that human ancestors would have had to endure. Chimpanzees are well suited for life in the trees, where their quadrupedal dexterity and opposable thumbs allow them easy movement, and on the ground, where they knuckle-walk like the other African apes. Male chimpanzees are approximately 1.2 m (4 ft) tall and weigh60 kg (132 lbs). Females are 1.1 m (3.5 ft) tall and weigh 47 kg(103.6 lbs). Chimpanzees live an average of 30 to 40 years in the wild and longer in captivity.

Chimpanzees have stout bodies with relatively long arms. They have a round head with large, projecting ears and small, forward-facing nostrils on a prognathous muzzle. The top of a chimpanzee skull is flat and is without a sagittal crest. Chimpanzees have large teeth when compared with humans, but have the same dental formula:2123/2123 = 32. Chimpanzee senses are similar to human senses; however, they have more effective olfactory functions.

There are 13 different categories for chimpanzee calls that range from soft grunts to loud pant-hoots and shrieks. Chimpanzee calls are distinguished from bonobos by being a lower pitch.

Chimpanzees exhibit a high degree of sexual dimorphism. Males are larger and stronger, with characteristically large testes and prominent genitalia. Sexually mature females can be recognized by the pink swellings of perineal skin that are present during the estrous cycle. The estrous cycle is when a female is sexually receptive and fertile. This period lasts for 2 to 3 weeks and occurs every 4 to 6 weeks. Captive females reach sexual maturity at 8 to 9years of age and give birth for the first time at 10 to 11 years of age. Wild females mature and give birth 3 to 4 years later than captive females.

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