• Question: why are humans shaped like they are with 2 arms and legs y not 4 legs

    Asked by ben6930 to Asif, Laura, Lena, Sean on 21 Mar 2012.
    • Photo: Lena Ciric

      Lena Ciric answered on 21 Mar 2012:

      This is a great question. The answer is that we did have four legs once upon a time. These were great as we could get around well. But then we evolved to have arms because we slowly started using tools, and it became an advantage to have a set of limbs dedicated to using tools and a set for moving about. This was particularly useful for hunting. If you look at chimps and gorillas, they use their “arms” like we do ours but also for moving around – so they’re somewhere in between us and our four-legged friends.

    • Photo: Sean Murphy

      Sean Murphy answered on 21 Mar 2012:

      The fossil record shows that as we evolved we began using our front legs (arms) more and more, and this came with changes to our spine as we began to try and stand upon our back legs only. The reason we started using our arms more is due to our hands. Our hands developed an opposable thumb, allowing us to use tools and develop more accurate fine motor skills. The opposable thumb ensured that important human functions such as writing were possible. The extra ability of our hands meant that we decided to walk on two legs instead of four.

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