... to the brink of extinction. The African black rhinoceros, killed for its horn, which is prized as a medicine and aphrodisiac, is also critically endangered. The great auk and the passenger pigeon became extinct in the 19th and early 20th centuries because of over hunting, and the Carolina parakeet also died as a species because of the combination of over hunting and habitat ... ...

• Word Count: 2997
• Approx Pages: 12
• Grade Level: High School

... on every internal organ, on every shade of constitutional difference, on the whole machinery of life" (Darwin 83). The effects of nature may be slower than the breeder's effect on pigeon variety, but natural selection will improve "each organic being in relation to its organic and inorganic conditions of life" (Darwin 84). Instincts are a broader aspect of a species that natural selection ... ...

• Word Count: 3127
• Approx Pages: 13
• Has Bibliography
• Grade Level: Undergraduate