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He gave a group of young chimpanzees plenty of practice with mirrors, then anesthetized them and painted two obvious red spots above one eye and the opposite ear. When they awoke, he let them look in the mirror. You or I, in such a situation, would immediately see the marks and probably try to touch them o rub them off. So did the chimpanzees. They touched the spots the spots more often than they touched the same place in the opposite side of their face.
Many other spices have since been tested. Human children pass the test from about 18 months onwards. Of the four other species of great ape, chimpanzees, bonobos, and orangutans mostly do touch the spots, although they vary a lot, but gorillas do not.


I'm kind of puzzled by the part in bold. I mean, in this text there are only four species of great apes mentioned: chimpanzees, bonobos, orangutans and gorillas.
Still why 'the four other species of great ape,' not 'the four species of great ape'?
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Human children pass the test from about 18 months onwards. Of the four other species of great ape, chimpanzees, bonobos, and orangutans mostly do touch the spots, although they vary a lot, but gorillas do not.
If I'm not mistaken, there are five groups classified by biologists as "great apes" (Hominidae), and humans are one of them.
CJ
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OH! Dictionaries published here translate it as manlike apes, which is why I have been confused. Thanks, CJ!
By the way CJ, what exactly is the difference between 'the four other species' and 'the other four species'? 
Takadifference between 'the four other species' and 'the other four species'
None, though personally I tend to use the second one.
CJ
Great! Thanks, Jim! 
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