California Tim said:
Correction: Evolution asserts that species already must have spawned new and unrelated distinct species. It is accepted as the ONLY possible explanation for the existence of all distinct species on the planet, both plant and animal. Any attempt to refute this is spurned as fantasy. The evidence is thus wedged into the theory on the basis that no other explanation is possible - and then interpreted from that bias. It is not a symptom unique to Creationists.
An incorrect correction.
In the first place, the Theory of Evolution makes no assumption about how many original and unique creations of species there were. It only stipulates that however many there were, they have all evolved and produced new species.
All of the various species with a common ancestor are related. How could they not be?
The determination of which species are related to others by common ancestry, and what the current degree of relationship is, is a matter of research. Quite similar to researching a family tree, but without the advantage of finding birth certificates and similar documentation to help. Scientists have to rely solely on physical indicators of relationship.
It is also a hugely daunting task which has barely begun. With over a million species already catalogued, and an estimated 10 million not discovered yet, very few have been subjected to the detailed research required to establish firmly what their relationships are in detail. Broad outlines are easier to establish than fine details and are therefore much firmer.
Nevertheless, much has been learned, including how many species are related to the same common ancestor.
As it turns out, the evidence leads to the inescapable
conclusion (not assumption) that all living species are ultimately related to the same Universal Common Ancestor. If there ever were other original unique creations, those species have died out and left no trace either among living species or in the fossil record.
Because all living species go back to a single Universal Common Ancestor, they are all related to each other as well. Some are closely related (as sibling species) through a recent common ancestor. Some are rather like first cousins---related through a common "grandparent" species. And as one continues tracing the known phylogeny, the current species become less and less alike as their last common ancestor is more and more remote in time.
What many people forget about relationship through a common ancestor is that as you go back through the generations, the relationships among the ancestors becomes closer. Take your grandparent and the grandparent of your fourth cousin. They were second cousins to each other. And their grandparents were siblings--children of the same parent.
The same applies in phylogeny. A horse is quite distinct from a rhinoceros today---but the common ancestor of the horse and the common ancestor of the rhinoceros differed in only a few details of skull and tooth shape. They differed no more than a husky does from a wolf. The additional differences were accumulated since the two species split from each other and went their own separate ways.