Creationists often complain that science supposedly says there was only one universal ancestor of all livings and that along the way, we evolved both into, and then from, bacteria. But that doesn’t seem to be the case. 21st century revelations in genomic research now imply that the origins of evolution come quite a while after the origin of life. There are now indications that at the root of each of the largest possible taxonomic divisions, there was a point when “descent” (as it is currently understood) was not yet occuring, (at least not in any determinable lineage) and instead there was a sort of horozontal gene transfer going on which could not truly be considered part of the evolutionary process.
By definition, evolution requires inherited genetic frequencies, but the co-requirement of "descent with modification" only allows for one series of ancestors rather than multiple lines of largely unrelated ones being inexplicably blended together. While taxonomy still points to a single common ancestor for all eukaryotes, that ancestor seems to be one of two or maybe three cellular siblings who evidently did not all descend from any sort of shared conventional parent! So at the point where an actual evolutionary phylogeny began to take over more or less exclusively, the domain, Eukarya had evidently already emerged separately and quite distinct from either of the "prokaryote" lineages.
"The branching tree pattern of Darwin's theory is actually not seen
anywhere in the fossil record, unless we impose it with out own minds."
“Wrong, sir! Wrong!"
The only way to objectively categorize all sorts of life is by their common characters, those features shared by every member of that collective and only by them. This is how their traits become diagnostic and directly indicative of unique groups. Let us also remember that the first man to attempt to classify all living things was a convinced Christian creationist who knew of no other option as he had never heard of evolution, and had never even conceived of common ancestry, and therefore certainly wasn’t trying to defend or promote either one. But the system he originally devised, -which is still in use today- determines that everything that is truly alive can be divided into two main branches which each then continue diverging in an ongoing series of subdivisions emerging within parental sets, henceforth known as clades.
The accuracy of divisions at the base of Eukarya are still being explored, because Protista turned out to be way too diverse to be considered a single grouping. But there’s no speculation required to determine that humans definitely descend from eukaryotes because it is a verifiable fact that every one of our cells is initially nucleic.
Moving on, one notable subset of Eukarya is Opisthokonta, who's gammete cells have a single posterior flagellum. One subset of this this group is Metazoa, also known as Kingdom, Animalia, multicellular opisthokonts which must ingest other organisms in some sort of digestive tract in order to survive. The biological definition, and in fact even the common dictionary defintions describe humans as belonging to the animal kingdom. Creationists howl at that idea that they should be animals, but if you have any knowledge at all of what an animal even is, then you know that you are one! This isn’t a matter of opinion either; It is a fact, and we can prove it!
Taxonomy is based as much on an organism's physiognamy, reproduction, and development as it is on the form itself. For this reason, the animal kingdom is then divided between the sponges, and everything more advanced than that -including Bilateria. These are triploblast animals which at some stage of development are bilaterally-symetrical. One subset of that is Coelomata, bilaterally-symetrical animals with a tubular internal digestive cavity. One of its subsequent subdivisions is Deuterostomia, coelomates in which early development of the digestive tract begins with a blastopore opening the anal orafice before the one for the mouth.
This is a strange thing to have in common with every other 'higher" life form. If they were specially-created, one might think that any of them could develop by some other means, or in some other order. Maybe snails would develop like mammals, and fish develop like squids, something like that, something that wouldn't only indicate an inherited trait consistent with both the genetics and morphology of common ancestry. But instead, every vertebrate has red blood while chelicerates and mollusks all have blue blood, with no exceptions on either side. Everything we see in nature consistently adheres to everything we would expect of a chain of inherited variations carried down through flowering lines of descent, just as it is in this case too. Starfish, sea urchins, acorn worms and every single thing that ever had a spinal chord all develop the opening for the anus first. Isn't that odd? The common ancestry model obvious explains this fact, but to date no would-be critic of evolution has ever been able to offer any explanation of this, or any of the other trends we see in taxonomy.
The next definitely determinable division includes Chordata, Deuterostomes with a spinal chord. This group includes Craniates, which are Chordates with a brain enclosed inside a skull. A subset of this group also includes vertebrates, which also have spinal vertebrae descending from the skull. And the next subset is Gnathostomata, vertebrates that have all that plus a jawbone.
Remember that we’re only following one lineage, and that each of the left or right turns we take cause us to overlook the other branches that may become just as hugely diverse as the one we’re on; sometimes much more so. But staying on our course, the next fork in the road lies between Gnathostomes who’s skeletons are either cartilaginous or calcified. The right turn here leads us to Sarcopterygii, bony vertebrates which have both lungs and legs. One subset of that are the Stegocephalians; limbed vertebrates with digits on the ends of their appendages. This clade includes a sub-clade called Tetrapoda, which are now gill-less Stegocephalians which are skeletally-adapted for four limbs. Included in that are the Anthracosaurs, pentadactyl post-aquatic 'terrestrial' tetrapods. We now also begin to see more pronounced development of the brain.
One of the anthracosaurian subsets reveals a seemingly small aberration but one which is among the rarest and most profound because the difference is developmental. These are usually the most integral and therefore the hardest things to change, and normally wouldn’t be expected to be significant –unless the environment changed profoundly, as it would in the adaptation from sea to land. The development of the amnion made this transition possible, and was evidently inherited by all the mammals, reptiles, and birds to come since.
Here another division occurs, this time determined by the number of holes appearing in a particular place in the structure of the skull. On the one-hand we have Synapsids with one temporal fenestra. On the other hand, we have what are traditionally known as “reptiles”, starting with anapsids that have no temporal fenestra, and Diapsids which have two. That line can be shown to divide again between Lepidosaurs on one side, which divide into plesiosaurs and other things including lizards, which also divided into many different sub-groups including snakes. The Archosaurs on the other side also divide into crocodilians, phytosaurs, pterosaurs, and dinosaurs, which themselves divide again and again, and eventually include a subset we now know as birds.
"We should expect the phyla, the classes, the orders,
families, down to and including the genera at least;
each would appear fully-formed with no transitional forms."
“Wait a minute! Strike that. Reverse it. Thank you.”
All the taxonomic levels are readily evident of course with many more clades now than anyone ever expected to find –so many in fact that the original construct can no longer bear the weight of all the new data. But not all the organisms in these clades are yet “fully” in the forms we find familiar today because there are so many obvious transitions at every level. One of the many examples of that is a Synapsid subset known as Therapsids, with increasingly mammal-like skeletal formations as well as vestigial stages evident in the continually advancing development of the brain.
Within that set are Cynodonts, therapsids with canine teeth. They’re actually a parent clade of Theria, the mammals, themselves identified are endothermic warm-blooded therapsids with lactal glands. Even the ones who eventually lost their canines still belong to this group because some members of usually fangless mammals still have those teeth. That, and of course because even when something is born without one or more features diagnostic of its parents, it must still be recognized as part of that family.
All the mammals alive today belong to one of three major divisions which are only a fraction of the major mammal forms that used to exist. In some respects, the platypus is the sole surviving karyotype illustrating what was the norm of mammalian diversity but which is now found only in fossil record.
The most familiar race of modern mammals are eutherians, which have nipples like marsupials, but are born in a placenta. This clade contains many subgroups at various levels, one of which includes the clades for both bats and primates.
Remember how we can objectively verify that every member all these groups still belongs to every parent clade already listed, and we can do the same for every subdivision from this point on.
“Primates” are collectively defined as any gill-less, organic RNA/DNA protein-based, metabolic, metazoic, nucleic, diploid, bilaterally-symmetrical, endothermic, digestive, tryploblast, opisthokont, deuterostome coelemate with a spinal chord and 12 cranial nerves connecting to a limbic system in an enlarged cerebrial cortex with a reduced olfactory region inside a jawed-skull with specialized teeth including canines and premolars, forward-oriented fully-enclosed optical orbits, and a single temporal fenestra, -attached to a vertebrate hind-leg dominant tetrapoidal skeleton with a sacral pelvis, clavical, and wrist & ankle bones; and having lungs, tear ducts, body-wide hair follicles, lactal mammaries, opposable thumbs, and keratinized dermis with chitinous nails on all five digits on all four extremities, in addition to an embryonic development in amniotic fluid, leading to a placental birth and highly social lifestyle.
“And that’s what’s important. But you know, if anyone wants to believe
that they’re the descendants of a primate, they’re certainly welcome to do it.
I don’t know how far they will march that back...”
We don’t believe this because we want to! And why would we want to? We believe it because we can prove it really is true, and that applies to everyone whether you want to believe it or not. We’re not just saying you’ve descended from primates either; we’re saying you ARE a primate! Humans have been classified as primates since the 1700s when a Christian creationist scientist figured out what a primate was –and prompted other scientists to figure out why that applied to us.
It wouldn’t be this way if different “kinds” of life had been magically-created unrelated to anything else; not unless God wanted to trick us into believing everything had evolved. Because the phylogenetic tree of life is plainly evident from the bottom up to any objective observer who dares compare the anatomy of different sets of collective life forms. But it can be just as objectively confirmed from the top down when re-examined genetically. This is why it is referred to as a “twin-nested hierarchy”. But there’s still more than that because the evident development of physiology and morphology can be confirmed biochemically as well as chronologically in geology and developmentally in embryology. Why should that be? And how do creationists explain why it is that every living thing fits into all of these daughter sets within parent groups, each being derived according to apparently inherited traits? They don’t even try to explain any of that, or anything else. They won’t because they can’t, because evolution is the only explanation that accounts for any of this, and it explains it all.