Apologetics · Creation — The branching tree in the textbook does more persuading than any experiment ever has. It is worth asking how that diagram gets drawn.
Every biology student meets the same picture. A trunk at the bottom, branches splitting upward, every living thing landing on a twig somewhere near the top. It is clean, it is memorable, and it does something no data set can do on its own: it makes the story feel already settled before a single argument is made.
I want to take that diagram seriously rather than sneer at it, because the reasoning behind it is not stupid. But I also want to ask the question a careful man should ask of any picture that persuades this efficiently: what would it take for this drawing to be wrong, and would we be able to tell?
How the Tree Gets Drawn
The logic is straightforward. Similar structures imply shared ancestry. The bones in a human arm, a bat wing, a whale flipper, and a horse leg follow the same underlying pattern — one bone, two bones, a cluster, then digits. That shared pattern is called homology, and the inference is that these creatures inherited it from a common ancestor who had it first.
Fair enough. Similarity is real, and any honest account of biology has to explain it. The question is whether similarity has only one possible explanation.
The Cases That Cannot Be Inherited
Here is where the picture gets complicated, and it gets complicated from inside the field, not from outside it.
The octopus has a camera eye — lens, iris, retina, focusing apparatus — strikingly like a vertebrate eye. But no one places the octopus on our branch. The last common ancestor of an octopus and a man had nothing remotely like that eye. So the same structure has to be explained twice, independently.
Bats and dolphins both navigate by echolocation, an exquisitely engineered system of emission, reception, and real-time processing. One flies, one swims, and they sit on distant branches. Independent origin, again. And when researchers looked at the genes involved in high-frequency hearing, they found parallel changes in the sequences themselves — not merely similar solutions, but similar edits, arrived at separately.
The Tasmanian thylacine looked so much like a wolf that people called it one, though it was a marsupial — its skull a near match to an animal on a completely different limb of the tree. There are dozens of these cases, and they have a name: convergent evolution.
Watch What Just Happened to the Evidence
Now put the two moves side by side, because this is the whole point of the essay.
- When similarity fits the tree, it is called homology, and it is presented as strong evidence for common ancestry.
- When similarity contradicts the tree, it is called convergence, and it is absorbed as an interesting example of evolution repeating itself.
Either way, the theory is confirmed. Similarity supports it. Similarity that cannot support it also supports it. A framework that reads both outcomes as evidence in its favor is not thereby false — but it has quietly stopped being tested by that particular observation, and everyone in the conversation deserves to know that.
The Strongest Version of the Other Side
An argument you cannot state fairly is an argument you have not understood, so let me put the response at full strength.
Convergence is not a dodge invented to save a theory. It has a real rationale: physics constrains the options. If an organism is going to focus light, there are only so many ways to bend it. If it is going to move fast through water, the hydrodynamics push toward a torpedo body — which is why sharks, tuna, dolphins, and extinct marine reptiles all ended up shaped alike. Selection working on similar problems in similar environments can plausibly find similar answers, and predicting that in advance is not unreasonable.
That is a serious point, and it should be granted without grumbling.
But notice what granting it costs. The moment you say similar constraints produce similar structures in unrelated lineages, you have conceded that similarity by itself does not demonstrate ancestry. And that is precisely what the diagram was built on. You cannot use resemblance as proof of descent in chapter four and as proof of independent invention in chapter nine without telling the reader which rule is operating and why.
There is a further point worth making calmly. Common design predicts reuse. An engineer who has solved the lens problem well uses that solution across unrelated products; a shared architecture across the catalog is not evidence that the coffee maker descended from the refrigerator. Shared parts are exactly what you would expect from one mind building many things. That does not settle the argument — but it means the data do not belong to one side by default.
The Tree That Keeps Being Redrawn
There is a second, quieter difficulty. When molecular sequencing arrived, it was widely expected to confirm the tree built from anatomy. Sometimes it did. Often it did not — and it still does not consistently. Trees built from different genes in the same organisms can yield conflicting arrangements. Trees built from molecules can disagree with trees built from bones. The relationships at the base of major groups have been rearranged more than once in living memory.
The field has explanations for this — horizontal gene transfer, incomplete lineage sorting, long-branch attraction, differing rates of change — and these are genuine, studied phenomena, not fabrications. But they are also flexible enough to accommodate almost any conflicting result, which brings us back to the same question: what pattern of data would count against the picture rather than be folded into it?
Separate the Three Claims
Most arguments about this go badly because three different claims get bundled into one word. Pull them apart:
- Common descent — that living things share ancestry.
- Mechanism — that random mutation filtered by natural selection is sufficient to produce the machinery we observe.
- Naturalism — that whatever happened, no mind was involved.
The third does not follow from the first two, and it is not a scientific finding at all. It is a philosophical commitment carried into the laboratory before any evidence is examined. Yet in most popular presentations, evidence for the first is offered as though it establishes the third. That is the sleight of hand worth naming — not the fossils, not the sequencing, not the hard and often excellent work of the people doing it.
Let me also say plainly, because this house has more than one room in it: believing brothers differ over the age of the earth and over how much common ancestry the biblical text permits. Young-earth and old-earth Christians both confess a Creator, a real Adam, a real Fall, and a risen Christ. Those disagreements are worth having honestly, and they are not the argument being made here. The argument here is narrower: the tree diagram does not carry the philosophical freight it is routinely asked to carry.
After Their Kind
Genesis does something the diagram does not. It gives boundaries and it gives an Author.
“God created the great sea monsters and every living creature that moves, with which the waters swarmed after their kind, and every winged bird after its kind; and God saw that it was good.”
Genesis 1:21 (NASB1995)
And Paul explains why the shared architecture runs through everything — not because a trunk pushed it upward, but because a Person holds it together.
“For by Him all things were created, both in the heavens and on earth, visible and invisible… all things have been created through Him and for Him. He is before all things, and in Him all things hold together.”
Colossians 1:16–17 (NASB1995)
That is a coherent explanation for why a lens works the same way in an octopus and in your daughter’s eye. One Designer. One physics. One catalog.
A Diagram Is Not a Verdict
So do not be intimidated by the picture, and do not become the man who shouts about it either. Ask the calm question in the calm voice: Which rule are we using here — similarity as inheritance, or similarity as coincidence? And what would we expect to see if we were wrong? That question has never lost anyone a friendship, and it has started a great many honest conversations.
And then be clear about where your own confidence actually rests. Not on a branching chart, and not on winning an argument about beetle wings. The Christian faith is not staked on a diagram. It is staked on an event, in a specific city, with a date, witnessed by people who died rather than retract it.
“All things came into being through Him, and apart from Him nothing came into being that has come into being.”
John 1:3 (NASB1995)
The tree will be redrawn again; it always is. The empty tomb will not be.
Teaching the Word. Watching the Times.
— SmithForChrist