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THE LAST WORD Last words past and present at newscientist.com/lastword

Blow out standing by it since your effective typical arrangement is two pairs not been required. Additional
cross-sectional area will be larger. of them (known as pectoral and limbs could also impair the
Space movies regularly dispatch If the door only opens partially, pelvic fins) and a tail that actively animal’s mobility, camouflage,
characters through an explosively you are actually more likely to be propels the fish, plus additional or even its way of life entirely.
decompressed airlock. But how likely blown out because the opening is fins on the back or underside that Furthermore, it would take
is such a rapid ejection, taking into smaller and the blast will last provide stability. time and energy to grow these
account the victim’s location in the longer until the air in the airlock Evolution is very good at using extra limbs, which could be
airlock and its volume? Assuming they is exhausted. features that evolved for one diverted from growth of more
are wearing a spacesuit, what is the Holding on to something to purpose as a basis for something important body parts. This
best way to avoid expulsion, apart avoid being blown out will not else, and some ancient fish started might weaken the animal and,
from grabbing something solid? help much: your grip is unlikely living at the water’s edge, crawling in extreme cases, jeopardise it or
to be strong enough, and even if drive it to extinction. For instance,
Q By a sad coincidence, it is, your arm may be wrenched “ Holding on to something why would humans develop a tail
at about the time this question off. The best way to avoid such to avoid being blown out or a third leg? This would be a
was published (21 April), an an accident is to enter only small will not help... your arm waste of time and impair us.
aircraft passenger was killed in a airlocks with large doors, and stay may be wrenched off” There may have been some
similar way. An engine explosion near the wall opposite the door species that we don’t know about
blew a piece of metal through a until the airlock is depressurised. on muddy land using their four with extra limbs. They may have
window and the air escaping from Unfortunately, real airlocks tend pectoral and pelvic fins. We can been driven to extinction or
the plane blew (not sucked as the to have small doors because large see this today with fish called forced to adapt to survive.
media put it) a passenger partially doors have to be stronger and are mudskippers, whose two pairs Luke Worster
out of the window. harder to seal. of fins have become fleshy lobes Nottingham, UK
In practice, everything depends The first fictional account of so they can skip through mud
on the geometry. In a passenger someone being dispatched in this when not in the water. Q Well, there are – giant squid for
plane, the volume of air inside is way may be the defenestration Over millions of years, fish like example, and octopuses. But for
usually quite large compared with of Oddjob from a plane by James these evolved into amphibians land animals, it is a consequence
the size of the opening, so the air Bond in Goldfinger, Ian Fleming’s and later into full land animals, of the history of life on Earth. Big
will be blowing out for some time 1959 novel. and their four fins ended up as land animals are all “tetrapods”
until the pressure is equalised. Richard Parkins proper legs. The other fins were (originally meaning animals with
In a spacecraft airlock, the door Cambridge, UK single ones, so were no good for four legs) because insects, which
is likely to be larger than a plane evolving into legs, as they would have more legs, can’t grow big
window, and the volume of the have just made walking awkward. enough. They have a different
airlock smaller, but the outside Legging it And don’t forget, four legs have type of respiratory system, one
pressure will be zero. The pressure proved perfectly adequate for that limits their size with the
inside can’t be too low otherwise Why aren’t there any big animals animals. It would have been a amount of oxygen that is in
the spacecraft passengers will (not insects) with six legs, or eight waste of energy (requiring more Earth’s atmosphere now.
suffer from anoxia when not legs or more than this? food) to start evolving more. Some tetrapods have lost
wearing spacesuits. So the Richard Swifte limbs (like snakes), and some have
pressure difference is greater and Q The answer lies with evolution Darmstadt, Germany become animals that stand on just
the initial blast will be stronger, and natural selection. Land two limbs (birds and humans).
but the lower volume means it animals with four legs evolved Q A big animal would not develop But it would be too much of a
will not last as long as on an from fish, and their legs were six or more legs unless a certain mutation to suddenly have six
aircraft. If you are near the airlock originally fins. Fish have evolutionary variation was limbs, or eight, instead of four.
door, you could very possibly be developed a variety of fins to needed to increase the success of Eric Kvaalen
blown out, particularly if you are enable them to swim, and a this animal, and this variation has Les Essarts-le-Roi, France

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