The genetic data overwhelmingly upholds common decent. your quotes are also by scientists who believe in universal common decent...Maybe you should actually go read the source material.
They believe it (accept it) but admit there is no proof. We share genes in common for many reasons. IN some instances, the same genes produce different results in different creatures and in others very different genes code for the same effect. Most of what is called "Junk" is actually the program necessary for life to be sustained by a form. Then of course dogs, bears, etc., share a bit more genes in common to relegate their forms and functions which differ from ape-kind in all its varieties which differ from human-kind, etc., but these have to do with differences of form and function (some of which many creatures share in common) but these to not necessitate common descent as if in the start of life single celled organisms after their miraculous development became multicellular organisms which became Metazoans and so on...as Catastrophe theorists and Punctuated Equilibrium theorists have noted species in the geo-column do not arise from a steady transformation from their ancestors but appear fully formed with all their functionally inter-dependent subsystems in place...no Nautilus then Nautilus...no fish then fish...this does not necessitate that Nautilus eventually became fish (or fish Amphibians, or Amphi's into reptiles, or reptiles into birds) it is just one way of interpreting the data (best guess based on the accepted theory)
Dolittle and Baptiste state "Darwin claimed that a unique inclusively hierarchical pattern of relationships between all organisms based on their similarities and differences [the Tree of Life (TOL)] was a fact of nature, for which evolution, and in particular a branching process of descent with modification, was the explanation. However, there is no independent evidence that the natural order is an inclusive hierarchy, and incorporation of prokaryotes into the TOL is especially problematic. The only data sets from which we might construct a universal hierarchy including prokaryotes, the sequences of genes, often disagree and can seldom be proven to agree. Hierarchical structure can always be imposed on or extracted from such data sets by algorithms designed to do so, but at its base the universal TOL rests on an unproven assumption about pattern that, given what we know about process, is unlikely to be broadly true. This is not to say that similarities and differences between organisms are not to be accounted for by evolutionary mechanisms, but descent with modification is only one of these mechanisms, and a single tree-like pattern is not the necessary (or expected) result of their collective operation."
The theory has been imposed on the evidence and most of it depends on the use of Homology and other such interpretive hypothesizing. All felines more than likely have a fewer base pairs of original species with the genetic capability to produce all this variety, Same with Canines but I do not see the evidence dictates Felines once shared a common ancestor with Canines (who also had their basic pairs capable of providing the information necessary to account for all their varieties.