Aussie lungfish study reported in New Scientist, 11/9/99 p25 found the Australian lungfish, Neoceratodus forsteri, uses the same protective proteins as those in human lungs. The only difference was that all cells in the fish lung lining made the protein whereas all other air breathing vertebrates have specialised cells for making these proteins. The researchers offered no explanation for where such proteins originated. Their only conclusion was they must have been preserved for 300 million years.
To breathe air the surfaces of your lungs must be covered with a thin film of fluid to dissolve the air and protect the cells forming the air sacs in the lungs. Surface tension of this fluid tends to make the air sacs collapse each time you breathe out making them very difficult to open for the next breath. For such lungs to function properly the air sacs must be kept open all the time, a problem easily solved by the use of proteins called surfactant chemicals- a solution of protein and phospholipid made by cells in the air sacs.
Editorial Comment: These findings are exactly what you would expect if air breathing creatures, whether lungfish or people, were created fully functional creatures. Each life form is a unique arrangement of non-unique features. Finding fully functional surfactant in the lungfish lung provides no evidence for it evolving ‘naturally’ from any other chemicals, and lungfish couldn’t work as lungfishes without it. (Ref. lungs. lungfish, surfactant)