10 things you’ve always wondered about humans, explained.



1. Why do women test perfume on their wrists?

In order to smell perfume it has to be vapourised using heat, and as there are lots of blood vessels just under the skin surface of the wrist it is a warm part of the body where the perfume will vapourise quickly.

2. Cocaine can enter the bloodstream by being sniffed, so why can’t diabetics inhale Insulin instesd of having to inject it?

To pass into the blood vessels in the nose drugs must pass through the thin epithelium lining the nasal passages, but drugs which are not fat soluble cannot pass through the phospholipid bilayer of cells, and as Insulin is not fat soluble (whereas cocaine is) it wouldn’t be able to pass through the nasal cells to enter the bloodstream.

3. Why have we not selected against and eradicated genes from the human genomw which cause ageing?

In order for genes to be passed on, the orgnism must reach reproductive age, so any characteristics, and therefore genes, which help the organism to survive so it can breed will mean the organism is more lkely to survive and pass those genes on. However, genes which cause ageing have no affect upon the survival of the species as these characteristics are only expressed after reproduction.

4. Why does one year seem longer to a child?

Time is relative. A child of 10 will think a year is very long as it is 10% of all the time they’ve lived so far, but to a 50-year-old one year is only 2% of  all the time they’ve lived, so as one year is a much larger proportion of a child’s life it appears much longer to them, and this is also why time appears to speed up as we get older.

5. If humans are so sophisticated why to we only have 46 chromosones when some plants such as ferns have around 1320?

Numbers of chromosones have nothing to do with sophistication, rather they are indicator of the age of the species. As ferns have been evolving for millions of years they have experienced more mutations in their chromosones which has led to an increase overall in the number of chromosones.

6. Why is milk white when tears and sweat are colourless?

It is simply down to the fact that milk contains fat forming a white-coloured emulsion whereas sweat and tears only contain mainly water and salts.

7. Why do our shins, which often suffer when we walk into something, have so little protection?

Our ancestors walked on all fours and so their shins would be on their hind legs and were rarely banged into so there was no need to protect them.

8. Why do females of other species, such as dogs, have much less painful pregnancies?

Animals who walk on four legs havethe weight of their offspring shared equally between four legs instead of two, and their backbone provides a horizontal support. As we walk on two legs the weight of the baby pulls forward, which is why many pregnant women experience severe backache.

9. Why do we have two sets of teeth?  

If we only had one set, as the jaw continued to grow during childhood, gaps would appear between our teeth as teeth cannot grow sideways, so we need a second set for when our jaw has stopped growing.

10. Why are more people dying each year from cancer nowadays, depsite huge advances in medical treatment and improving survival rates?

Vaccination has meant that very few people each year die from diseases such TB, polio, pneumonia etc and so as this has greatly increased our life expectancy, and our population is continually increasing,  more people are reaching the older age groups where cell mutations, i.e. cancer, occurs more frequently.


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