J. B. S. HALDANE 
able to introduce small fragments of the genome of one species 
of fly into another with which it gives sterile hybrids, and the 
same has since been done with bacteria. Such intranuclear 
grafting might enable our descendants to incorporate many 
valuable capacities of other species without losing those which 
are specifically human. Perhaps even 10,000 years hence this 
will be a wild project, but techniques progress very rapidly. 
The fifth question is highly speculative, but it is time that 
systematic speculation started on it. The most obvious abnor- 
malities in extra-terrestrial environments are differences in 
gravitation, temperature, air pressure, air composition, and 
radiation (including high speed material particles). Clearly a 
gibbon is better preadapted than a man for life in a low gravita- 
tional field, such as that of a space ship, an asteroid, or perhaps 
even the moon. A platyrhine with a prehensile tail is even more 
so. Gene grafting may make it possible to incorporate such 
features into the human stocks. The human legs and much of 
the pelvis are not wanted. Men who had lost their legs by 
accident or mutation would be specially qualified as astronauts. 
If a drug is discovered with an action like that of thalidomide, 
but on the leg rudiments only, not the arms, it may be useful to 
prepare the crew of the first spaceship to the Alpha Centauri 
system, thus reducing not only their weight, but their food and 
oxygen requirements. A regressive mutation to the condition 
of our ancestors in the mid-pliocene, with prehensile feet, no 
appreciable heels, and an ape-like pelvis, would be still better. 
There is no immediate prospect of men encountering high 
gravitational fields, as they will when they reach the solid or 
liquid surface of Jupiter. Presumably they should be short- 
legged or quadrupedal. I would back an achondroplasic against 
a normal man on Jupiter. 
Human capacities for temperature adaptation are rather 
limited, and the invention of clothing renders them unimportant. 
When allowance is made for water vapour and carbon dioxide, 
a supply of pure oxygen at a fifth of an atmosphere would not 
suffice most humans. At air pressures below about a quarter of 
an atmosphere a pressure suit is needed. I may remark that my 
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