Do humans still possess the genes for gills?
I’ve heard that human embryos develop slits that resemble gills, but that these disappear long before the person is born. I’ve also heard that humans still possess the genes for gills, but these genes are never activated. Is this true? If these genes were somehow turned on, would it be possible for humans to breathe underwater, or would it also require other huge changes to things like the lungs?
One Response
Cal King
21 Nov 2009
Human embryos develop gill slits, but then development stops and gills never become fully developed. Even if we still possess the genes that encode fully developed gills, they may have degenerated.
In animals that have fully functional gills, these genes are highly conserved because of natural selection. Any deleterious mutation that would result in non-functional gills would then be weeded out. The same mutations, if it happens to a human’s gill gene, would have no effect on survival because natural selection cannot act upon the genes, only their products. Therefore practically any nucleotide change would be neutral, confering neither an advantage nor a disadvantage to the individual. A neutral molecule is a systematist’s best friend, because they change in a clock-like manner, and they can be used as molecular clocks to determine relationships. Since humans evolved from land animals that have been free of the water for over 3 hundred million years, even if we still possess the genes for gills, chances are that they have accumulated so many nucleotide substitutions they would not be functional.
In short, there is practical no chance for humans to ever develop gills even if we still have the genes, because they have undergone so much mutation over 300 million years.