Hello everyone. I'm reading a published scientific paper (trying to start interning at the biodesign institute at my college and this is some "homework" i got), and have no idea what those 2 terms mean. It's used in many places throughout.
EDIT: okay, I think more info is needed. The paper can be read here. It's not long. It's a study about human rhodopsin (visual pigment) mutations which lead to retinal diseases. Here's a couple examples of sentences using the phrase:
"For a given amino acid site, the average chemical severity of interspecific substitutions is a simple average of the severity of all ancestor-descendent amino acid differences throughout the tree."
and
"From a neutral theory perspective, the direction of difference in the chemical severity of disease mutations is expected, but the magnitude of this difference is not predicted by any existing theory."
Any shedding of light on this will be greatly appreciated
