I use Gas / Carbon Dioxide for my Nerdon race. I chose Gas because...well...Nerds tend to stink so I thought them living on a "gassy" world fit.
I chose Carbon Dioxide because at my work, we call people who are useless "CO2 makers", meaning all they are good for is breathing. Thought it would be a race with a little style (very little!
.
Oh, of course I set my reproduction rate to 91%...Nerds just can't seem to find many dates..
I hope I have not offended any fellow nerds!
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Regards,
KiloOhm