THE LAST WORD

The bottom of itNon-human animals do not use lavatory paper, and those that I have observed don’t appear to need it. Are there anatomical reasons for this? If so, why is our anatomy not similar to that of the great apes? Has our invention of lavatory paper, and whatever methods preceded it, meant that we have lost an anatomical feature that we once had?

n 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.

We also differ from other animals in our response to our waste, which we tend to regard with disgust. This seems to have developed as a result of living together in settlements rather than roaming through the forest,

where we could leave our mess behind us. Unlike other primates we can learn when and where it is acceptable to excrete.

Disgust is a sensible response to the threat of pathogens in human waste, and civilisation itself would be impossible without some system of sanitation. We have house-trained ourselves to the point where we are repelled by the very smell of our waste, and thorough cleansing has become a necessity for social reasons as much as for hygiene.

Human ingenuity in this respect has now gone far beyond toilet paper and wet wipes. In Japan there are toilets which will wash and blow-dry your most delicate areas without any effort on your part.

On the other hand, the 16th-century French writer François Rabelais recommended using the softly feathered neck of a live goose for the ultimate in cleanliness and comfort.Christine WarmanSaltburn-by-the-Sea, North Yorkshire, UK

n Although animals seem to have no such inhibitions, the anal area isn’t one that humans like to think about. Yet cleanliness around this part of the body is crucial to survival, as it is particularly susceptible to bacterial and parasitic infection.

The anus is a sphincter, a muscular ring, under voluntary control. A useful aspect of its design is that a slight prolapse of the rectum occurs when

defecating, minimising contamination of the external area. Also, taking up a squatting position ensures that faeces do not come into contact with any other part of the body. Contamination does occur sometimes, though, and this is where good grooming comes in.

Wild animals, especially carnivores whose faecal matter contains material attractive to pathogens, have evolved to be able to clean themselves. You only have to watch cats “playing the cello”, as it is colloquially called, to see how proficient they are at grooming their rear. Parents will clean their young until they are supple enough to do it themselves. Adult animals will also groom each other, forming social bonds at the same time.

Domesticated animals selectively bred by us are a different case. My dog, for example, cannot clean his hind quarters because he is too short and stocky in the body; we have to check that he is clean after he has defecated.

Similarly, sheep have to be inspected regularly because

their body shape prevents them from keeping themselves clean.

Many species, humans included, have adapted their front legs to be hands – helpful for self-grooming. The use of plant

material to clean the anal area would have been an evolutionary adaptation. Vegetable matter was substituted with a sponge on a stick in Roman times, and more recently with paper.Tony HolkhamBoncath, Pembrokeshire, UK

This week’s questionsCondimenT CleanerI recently read with interest in The Last Word of somebody using lemon juice to clean a bar top made of zinc. It was effective, but the process gave off a terrible smell. I work in a restaurant with a copper bar top. We clean it with tomato ketchup, which works really well and, more importantly, doesn’t produce a bad odour. So why does ketchup clean a copper surface without smelling terrible, unlike lemon juice on zinc?Marcim JakubowskiLondon, UK

eCho disloCaTionOn a recent holiday in Italy, my wife and I enjoyed a piano recital in Ravello, on the Amalfi coast. It took place in an old, open-sided stone building which seemed to form part of the hunting area of a small bat seen flying around before and during the concert. At one point the bat circled energetically above the pianist for a couple of minutes. What impact, if any, would the music have had on the bat’s sonar?Andy ClarkeSt Albans, Hertfordshire, UK

“ humans walk tall and so have problems with backs and joints, and evacuating waste is more difficult”

“ You only have to watch cats ‘playing the cello’ to see how proficient they are at grooming their rear”

last words past and present at newscientist.com/topic/lastword

sponsored by

The writers of answers published in the magazine will receive a cheque for £25 (or US$ equivalent). Answers should be concise. We reserve the right to edit items for clarity and style. Include a daytime telephone number and email address if you have one. We are pleased to acknowledge financial support from Statoil in producing The Last Word. New Scientist retains total editorial control over the content.

Reed Business Information Ltd reserves all rights to reuse question

and answer material that has been submitted by readers in any medium or in any format.

Send questions and answers to The Last Word, New Scientist, Lacon House, 84 Theobald’s Road, London WC1X 8NS, UK, by email to lastword@newscientist.com or visit www.newscientist.com/topic/lastword (please include a postal address in order to receive payment for answers). Unanswered questions can also be found at this URL.

Win £100 by answering our monthly question about energy issues

How much energy is in a lightning bolt? Is it enough, and are there places where lightning strikes often enough, to think about flying kites to transfer that energy to the grid?

Answers should reach us by 23.59 GMT on 14 January 2014 to answers@newscientist.com or visit www.newscientist.com/topic/energy. Terms and conditions are also at this URL.

The lasT Word on energy

140111_R_LastWord.indd 149 2/1/14 15:25:28