Bilirubin is a by-product of red blood cell breakdown which is a mammilian specific by-product of red blood cell breakdown. Reptiles, amphibians, and birds all have red blood cells break down in heme then to biliverdin, something they are able to excrete without any addtional breadown. Mammals, on the other hand, have the bilirubin break down into biliruben. One of the key evoltionaly differences between mammals and these other species is the placenta connecting the mother and child together. Since this trait has evolved and been conserved through mammels, it begs the question if there is a benifit to having biliruben in the system of infants. Biliruben is an antioxident that could prevent DNA damage during the development fo the fetus.
In utero, the fetus’s red blood cells break down and is filtered through the placenta. From there, the mother breaks down the bilirubin into the expendable form in their liver and its rid of waste. When a baby is born, it is disconnected from the mother and its liver is not fully functional so it cannot breakdown the bilirubin themselves. If levels of bilirubin are too high, the baby can be diagnosed with hyperbilirubin which appears are jaundice in the baby. This is concerning to doctors taking care of the newborns becuase if the levels of biliruben are too high, then the child would be left with serious brain damage. Depending on how much jaundice the newborn is presenting, they are placed under lights to reduce the levels of biliruben. If the levels of biliruben in newborns did not benefit the fitness of the child, then natural section should have weeded it out.