How The Lamprey Eel's "Cough" May Have Evolved into Lungs:

The lamprey is, according to this study, the most basal (closest to the bottom of the phylogeny tree) vertebrate in terms of the evolution of the lung. One of the most critical elements of breathing is the neurological element of a "rhythm generator". This rhythm generator must be sensitive to metabolically produced CO2 and be able to rhythmically activate based on the levels of CO2 present/metabolic demand. This is what allows our bodies, and all bodies that breathe like we do, to breathe automatically.

While lamprey eels may not have lungs specifically, they do have what has been identified as the very first rhythm generator to evolve. In order to gather nutrients, lampreys bury themselves in the sediment of bodies of water and generate a rhythmic flow of water through their bodies. This water flow not only collects nutrients, but satisfies metabolic gas exchange requirements. This slow rhythm generation is also called the lamprey's "cough".

Additionally, the researchers isolated lamprey brain stems and found that they rhythmically stimulate the ventilatory muscles that allow for this rhythmic water flow.

So, anyway, we have these weird looking guys to thank for the fact that we breathe automatically.