/sci/ - Science & Math

>>3072423

Hi /sci/ - have a completely stupid question here. After many years of running away from math and physics (education-wise:).. I finally fell in love with both. So now I'm watching enormous amounts of science shows/interviews/lectures online. The last joy of the heart is ttc (watching dark matter/dark energy now). I just always wondered how do people derive equations. Do they derive everything from basic ones (i.e Newton's) or they just sit and think 'hm.. if I add up space curvature and space expansion, i should get mass density times something:)

All of the basic animal types that we know. (mammals, birds, fish, not scientific categories or families) all have different numbers of heart valves. We have 4, birds have 3, reptiles have 2, and fish have 1. Isn't that neat?