Question: what would happen if we had 3 lungs?

Steve Faulkner answered on 13 Mar 2012:

Assuming that having 3 lungs would have no adverse affect on your health and well being, a third lung would be beneficial for many types of activity. One of the limiting factors in exercise capacity is the amount of oxygen that can be taken up and used by the body during exercise (VO2 max) and this is largely predetermined by your lung volume. Therefore, if you had a third lung of equal size to the other two, then you could expect to see an increase in you VO2 max of around 33%. THis would dramatically improve your ability to deliver oxygen to the working muscle more rapidly and in greater volume, thus allowing them to contract faster for a longer period of time. In essence, it would allow you to run faster for longer!