Thank you!
My understanding from years ago is that whales, being mammals, are thought to have evolved from land based animals. I don't know how controversial such a theory would have been prior to the discovery of these viral DNA markers, but I would think that it might now be possible to be more certain.
The virus remnants are just one genetic tool. We have several ways of establishing these relationships. Paleontologists piece together phylogenies based on bone measurements, for instance, by measuring the ratios of various parts of a bone and comparing those ratios between species. They also look at other bone features. Since I never studied paleontology, what they do really looks like magic to me. However, by doing what I know best--molecular biology--I look at DNA homologies, not just of the viral remnants, but of any part of the genome that I want to study, and I can reconstruct the same phylogenetic tree that the paleontologist constructed. I love phylogenetic trees; they can be used to examine any evolutionary relationship, no matter how closely or distantly related the organisms are.
This picture is the phylogeny of a single gene on Y chromosomes of European men. These men are all related. I would guess that the alphanumeric code is an identifier for each man in the tree.
Another fact I ran across recently is that mushrooms can be a dietary source of vitamin D if the mushrooms are exposed to sunlight.
I believe that not all organisms are able to synthesize vitamin D from sunlight. Is the presence of this capability consistent with viral DNA, or am I barking up the wrong phylogenetic tree?
Interesting! I do not know enough about mushrooms to know how much of their metabolism is affected by the presence of viral genes. The thing is, viruses and more complicated organisms rely on each other. We exchange genes with each other, and we are true symbiotes in that we perform biological functions for viruses, bacteria, and fungi, and they perform vital functions for us. Although most people think of germs as destructive invaders, the truth is that most of them are not pathogens and have mutual cooperation agreements with their hosts.