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"Ms. Warman notes, "Although we share most of our DNA with great apes, there are some striking anatomical differences between ourselves and our nearest relatives, most notably our vertical posture. This enables us to walk tall with our hands free, but it also comes at a price: we experience problems with our back and joints, and the whole business of evacuating our waste is more difficult. The fundamental problem is that the area used for releasing urine and faeces is compressed between thighs and buttocks, so we are more likely than other animals to foul ourselves."