Homology: Common Ancestry, or Common Designer?
If you ask someone to prove to you that evolution is true, you might hear something like this:
“Antibiotic resistant bacteria show evolution in action.”
“The fossil record shows the evolutionary progression of primitive animals into complex ones.”
“The homology of the vertebrate limb proves the common ancestry of vertebrates.”
If you were to then ask someone to prove to you that creation is true, they might list you some of these evidences:
“Antibiotic resistant bacteria show genetic diversification within a bacteria kind.”
“The fossil record shows the progression of animals captured by the march of waters from the Great Flood – first sessile or slow moving ocean bottom-dwellers, and upwards to more mobile land dwelling animals.”
“The homology of the vertebrate limb proves the common Designer of all vertebrates.”
The point is that evolutionists and creationist have the exact same world, evidence, fossils, genetics, animals, and universe to prove their point of view. The problem is they interpret the evidence in different ways.
Sometimes it can seem like one explanation is better than the other, but in the case of homology, I used to see each explanation sort of as though they were both equally plausible – neither was more definite than the other, but the validity of each was based on the validity of the perspective that it came from.
I recently learned that that is not the case. The creationist’s explanation for homology – that it is evidence for a common Designer – is actually a much more logical explanation for homology than the common ancestry evolutionists claim about it.
In fact, there are examples of homology that fit so well with the creationist model and conflict so much with evolution, that evolutionists don't even refer to it as homology - they refer to it as analogy instead.
Example #1: Fusiform Shapes
The swift and sleek shaped of a shark is referred to as fusiform. It is also seen in dolphins, orcas, tuna, and ichthyosaurs - an extinct marine reptile.
In other words, this extremely aerodynamic body plan is seen in distantly related fish (sharks and tuna), mammals (dolphins and orcas - and they had to evolve that from land mammals) and reptiles (again - land reptiles evolved first, so ichthyosaurs had to evolve from them).
This homology is not evidence for common ancestry at all. Instead, evolutionists must believe that the fusiform body plan evolved independently at least three times.
Example #2: Rotifers vs. Tardigrades
This one needs a little background in animal taxonomy and their presumed evolution. There are two major groups of animals: dueterostomes and protostomes.
(You can skip this paragraph if you don't care about the differences, fyi). Their differences lie largely in their development. For example, in protostomes, the mouth forms first in the embryo. In dueterostomes, the anus forms first. Protostomes have mosaic development, in which the location of new cells determines what they will differentiate into. When a zygote first starts dividing into lots of little cells, the embryo's size doesn't change. Instead, the new cells remain in place, and divide until they get very small. Cells near the top of the original zygote will eventually become the head, and cells near the bottom will eventually become the feet (or tail, or whatever, depending on the organism). This means that if you chop a protostome embryo in half before the cells start to differentiate, you will end up with two halves of an animal. Deuterostomes do not do this; their cells differentiate based on their position relative to each other. If you chop a deuterostome embryo in half before the cells differentiate, you will end up with two whole animals.
Anyway most animals are protostomes; very few animals are deuterstomes. We are deuterostomes, along with the echinoderms (sea stars!) and a few other obscure critters. But protostomes includes a wide variety of organisms, and according to evolutionists, they evolved first.
The protostomes are divided into two main groups as well, which also branched out early and evolved separately. The two groups are the lophotrochozoans and the ecdysozoans. We won't bother ourselves with their differences here, but the main point is they are very, very evolutionarily distinct from each other - more so than mammals and birds are, and even more so than chordates (all animals with a backbone, i.e. every animal you think about when you hear "animal") and echinoderms (an invertebrate).
One of the phyla within the lophotrochozoan clade includes the Rotifers, and one of the phyla within the ecdysozoa clade is the Tardigrades. Rotifers are microscopic animals that are very mobile; tardigrades are microscopic animals somewhat similar to the arthropods (insects, crabs, etc.)
Tardigrades and Rotifers, despite being from to very evolutionary distinct clades of animals, actually share many similarities, which confused taxonomists for a long time.
Another type of ecdysozoan is another arthropod-like phylum, the Onychophorans. These little animals (affectionately referred to as velvet worms) share many similarities with Annelids (including earthworms). Annelids are a type of lophotrochozoan.
Despite these issues, tardigrades and onychophorans share just enough similarities between each other to be considered sister-phyla, and the similarities they share with the other two lophotrochozoan groups are ignored or dismissed as happenstance. Such similarities - dare I say, homologies - are inexplicable within the theory of evolution.
Example #3: Biochemistry
Every single animal on the planet uses the same - or very similar - biochemical pathways. The DNA of a human being is 50% similar to the DNA of a banana. The genes for bioluminescence in jellyfish are similar to the genes for bioluminescence in fireflies.
The genetic code is universal in many ways. There are genes that exist in one animal, but if placed in the DNA of another animal, are read the exact same way.
This has lead to some fun results. Biotechnologists have actually taken the gene for bioluminescence and inserted it into some fish. The result? Glo-Fish, or glow in the dark fish you can buy in your local pet store!
Taxonomically, jellies and fish are extremely separated. Jellies are one of the earliest, most primitive creatures - both protostomes and lophotrochozoans, if you didn't fall asleep while reading the above section - and more than that, they are separated from others of their clade by being diploblastic (all but two other lophotrochozoan phyla are triploblastic). Fish, on the other hand, are all the way over at the other end of the animal spectrum - members of the deuterostome clade, in the most recently evolved chordate phylum.
Yes somehow, a jelly's gene for emitting light can be read by the cells in a fish? That is very good evidence for a common Designer, who used similar biochemical and genetic pathways for all His creations!
Example #4: Developmental Biology
We've been talking about homology across the animal kingdom (mostly), but what about homology between plants and animals?
Remarkably, such a thing exists. We've discussed animal embryo development, from a zygote to a blastula (blastula is the technical term for a ball of cells before they have differentiated). Both plants and animals have this blastula, however. After the blastula has formed, the cells need to start spreading around to their own location.
When they have reached where they need to be, the cells need to start differentiating. In an animal, that differentiation can lead to nerve cells, liver cells, muscle cells, etc. In a plant embryo, differentiation can lead to different types of plant tissue cells.
How does each cell know what type of cell it is supposed to become?
The answer is Homeobox genes. These genes control the development and differentiation of other cells within an embryo. There are different types of homeobox genes; plants use MADS genes, and animals use HOX genes.
Within HOX genes alone there is very little similarity. Only one of fifty genes sets an insect HOX gene apart from a mammal HOX gene. Not only that, but animals' HOX genes and plants' MADS genes are both extremely similar - and they operate using the exact same method.
According to one evolutionary biology textbook, this is "a beautiful example of convergence, and strong evidence for the claim that this method of control must be an extremely good one."
Convergence? Convergent evolution is where two organisms with distinct evolutionary paths evolve ridiculously similar structures - i.e., evolve "analogous" structures.
And is all that this is evidence for is a really good control mechanism? Certainly no one disputes that. But it is also evidence for something else - an infinitely wise Designer equipped both plants and animals with a superb method of development.
Evolution: An Introduction by Stearns & Hoekstra.
Acts & Facts from ICR.
Integrate Principles of Zoology by Hickman.
The Code of Life: DNA by Purdom.
Developmental Biology by Gilbert.