Surely, even if 'common ancestor' is taken to refer to a single individual, it's still a logical necessity for everything to have a common ancestor with everything else (assuming common descent). There wouldn't be a unique individual, and we could never hope to find or know if we've found such an individual, but how could they not exist?
Well, maybe. But, I don't think so.
If we take a strict gradualistic approach, any new evolutionary development must have occurred within a pool of organisms (or proto-organisms) that was just one step short of the new development. Interactions and exchanges between the organism with the new development and the other organisms in the pool are probably unavoidable.
I think this is probably true of every step in evolutionary history, although the very first true cell might be an exception (I don't think so though: HGT, prions and viruses were probably major contributors around that time).
I agree that "common ancestry" should not be used since it is too messy and it is based on speculation. The geographical environmental gene pool that defines a specific ecosystem is the primary initiator for evolution to take over for changes in appearances of the biota over time. That is a better explanation.
Common ancestry means two organisms share an ancestor.
Wherever there is reproduction, there is common ancestry. Wherever there is evolution, there is common ancestry between species.
It's pretty simple, it isn't messy, and it isn't based on speculation.
The only thing that's messy is identifying which organisms are common ancestors for which other organisms.
Could you please now add in Australopithecus, Homo habilis, Homo Rudolfensis, Homo Erectus, Homo Ergaster, Homo Heidelbergensis, Homo Neanderthal, Homo Cro-magnom, woodland apes. and then modern humans.
All of those are "humans" on Dr Adequate's diagram (except maybe for "woodland apes": I don't know what "woodland apes" are).
Did you use the Fitch parsimony method based on morphological analysis? If indeed, this is the case then you couldn’t add in the other species of human ape-like creatures in this diagram. There is no DNA evidence for all of them except Neanderthal and modern man. The molecular clock is unrealistic even for the ones you do have listed here. These models present hypothesis and in no way conclude that it is a fact.
DNA is not the only thing one can use, Barbara. There are dozens, maybe even hundreds, of tiny characteristics of bones that can be useful in determining whether a particular fossil is H. sapiens, H. erectus or a chimpanzee. For instance, chimpanzees have large canine teeth with huge, deep roots; and humans (H. sapiens, not the rest) have a chin (outward thickening of the jawbonw), whereas all the other hominids have a simian shelf (an inward thickening of the jawbone).
One can take many measurements and list many characteristics of skeletons, and input that into the same kind of parsimony analysis as used with DNA evidence, and yield nice trees just like the one Dr A made, and they can readily include fossil hominids in them.
Don't make the mistake of becoming an uncompromising modernist: molecules are not the only thing science can work with, and they're not the only things that can give useful results.
You can use a mouse as being as common ancestor if you wanted and use genetics as evidence. Would this be true
No, you actually can't use a mouse as the common ancestor.
Evidence based on genomes and on anatomy would clearly show you that mice are not good candidates for the common ancestor of humans and apes, because there are dozens of other groups of animals that are much better.
The human skull diagram that shows all of the species of ape-like man up to modern human is not clear of what is being proven here. You can take all breeds of dog's skulls and line them up and it will show various sizes in skulls, these are all living today.
But, dog breeds also all evolved out of a common stock, and we can sometimes trace the ancestry of breeds the same way we trace the ancestry of humans.
I'm sorry I thought that all breeds of dogs was man's creation
Man "created" dogs by selecting for the traits they wanted in the dogs. This is called "artificial selection."
Artificial selection works basically the same way as natural selection, except that artificial selection doesn't just favor survival and reproductive ability: it could favor any number of things (aesthetics, or human utility, for example).
It's still evolution. And, it's a great example of common ancestry for diverse forms of life.
It seems silly to say it's aesthetics that's being selected when some human only allows dogs who look in a certain way to breed, whlist it's reproductive ability being selected when some female wolf only allows wolves that look a certain way to mate with her.
But it's far from silly to say that it's aesthetics that's being selected for when humans choose who breeds, while it's reproductive ability being selected for when a population becomes dominated by females that give birth to larger litters.