Physical Strength - Some sort of bonus or penalty to ground combat. (To hit? Damage?)
Intelligence - Percent modifier to research
Cunning - Percent modifier to intelligence (as in spying, not the racial trait)
Environmental resistance - Supposedly makes hostile environments easier to live in. I read somewhere on this forum that every 5 points of this trait improves the effective conditions of any planet by 1 point, though. (10 points = 1 level, I think.)
Reproduction - Not a percent modifier to reproduction rate, but instead if you have 105% then your populations reproduce 5%/year faster, if you have 92% they reproduce 8%/year slower (very bad!)
Happiness - If you have 105% happiness I think your planets get 5 extra happiness points per turn. Or maybe you get 1 point for every X number of Happiness trait...
Aggressiveness - Adds or subtracts to your chance to hit with direct fire weapons. If you have 120% then you get an attack bonus of 20%.
Defensiveness - Like aggressiveness, but with defense. Makes it harder or easier for enemies to hit you.
Political Savvy - Percent modifier for resources, research, and intel gained by trade. Does NOT affect your chance of getting treaties with the AI players!
Mining Aptitude - Percent modifier to minerals generation. Don't know if it affects solar generators.
Farming Aptitude - Like Mining Aptitude but applies to organics.
Refining Aptitude - Like Mining Aptitude but applies to radioactives.
Construction Aptitude - Percent modifier for how fast your planets can build things.
Repair Aptitude - Percent modifier for how fast your repair bays and spaceyards can repair ships, and also for some reason affects the speed at which your ship-based spaceyards build.
Maintenance Aptitude - If you pick 105% then your maintenance cost is 5 percentage points lower than a normal race. If you pick 95% it's 5 percentage points higher.
Hope that helps!