Biological Possibilities in the Next Ten Thousand Years 
late father made and tested the first pressure suit. However an 
Andean or Tibetan might be able to live at an external pressure 
of a fifth of an atmosphere. If this is the approximate pressure 
on Mars, as some astrophysicists believe, it may be desirable to 
pick colonists with Andean or Tibetan ancestry; for a suit which 
allows breathing at a pressure a few millimetres above that out- 
side is both safer and more comfortable than if the difference is 
greater. I see no prospect, in the next ten thousand years, of 
adapting human beings to breathe air in which the partial pres- 
sure of oxygen is less than 1 per cent of a terrestrial atmosphere. 
On the other hand given an artificial breathing mixture, men 
can live quite happily, though for how long we do not yet know, 
at all pressures from } atmosphere to 20 atmospheres, and very 
likely at higher ones. 
The least understood danger is that from radiation and high 
speed particles. The ultraviolet and X-radiation from the sun 
could doubtless be kept out. But if Titov had got up into the 
streams of charged particles predicted by Bjerknes and more 
accurately by Chapman, detected more or less simultaneously 
by Soviet and American satellites, and now called the van Allen 
belts, or had run into a storm of particles ejected from the sun, 
he might have been seriously injured, or even killed. It may be 
known what thickness of heavy metal is needed to afford pro- 
tection against these particles. If so, it is a secret. Almost cer- 
tainly resistance to radiation is a desirable character in 
astronauts. It may or may not be attainable. It is a heritable 
character, though rare, in some bacteria. If there is a nuclear 
war, the survivors will have been heavily selected for radiation 
resistance, if such selection is possible. If so they will be suited 
for astronautics. Even if the danger is exaggerated it may be 
worth selecting resistant types when we know how to do so. 
Possibly other dangers will prove even more serious. It is 
reasonably sure, on the one hand that natural selection in space 
will hardly change a section of humanity very greatly in ten 
thousand years, and that on the other, new human characters 
will be sought for and perhaps bred for, or, as I have suggested 
in the case of asepsis, imposed artificially. 
all 30D 
