How humans evolved.

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http://www.wwnorton.com/college/anthro/bioanth/

Chapter 1: Adaptation by Natural Selection
All around us are organisms that seem almost perfect for their respective environments. From the woodpecker's beak to the specialized echolocation systems employed by bats, many life forms exhibit a wide variety of characteristics that allow them to effectively exploit their particular surroundings. However, the questions that are not easily answered concern the "how" and the "why" of adaptation. Prior to the middle of the nineteenth century, explanations for why animals and plants are so suited for their environments were based exclusively on the notion of divine creation. For some people, this is still the case. This conclusion combines theological and philosophical arguments with observations in the natural world. For example, William Paley's argument in his Natural Theology (1802) was based on the premise that the intricate machinery of a biological organism implies it had an intelligent, heavenly creator. In contrast to this "watchmaker argument," two young Englishmen—Charles Darwin and Alfred Russell Wallace—proposed a theory that explained the process of adaptation without attributing it to the influence of a higher, spiritual power.