What about vestigial organs like the appendix, or the gill-slits in fetuses? Surely you can't mean that makes more sense given theism than evolution?

The objection deserves a careful answer rather than a slogan, and part of it is correct: if a structure really were a functionless leftover, that would count as evidence for common descent. The question is whether the examples are what they are claimed to be.

1. Concede the principle. A genuinely useless organ, awkwardly cobbled together, is better evidence for descent than for design. Christians should grant that up front instead of pretending the argument has no force. The dispute is about the specific cases, not about whether such evidence would count.

2. Vestigial means reduced, not useless. In biology the word describes a structure that has lost most of its ancestral function. It is not a claim that the organ does nothing. That distinction matters, because the popular argument treats vestigial as a synonym for pointless, and then the organ turns out to have a job.

3. The appendix has immunology. The appendix contains lymphoid tissue and is part of gut-associated lymphoid tissue. A 2007 paper in the Journal of Theoretical Biology proposed it as a reservoir, a safe house where beneficial gut bacteria can survive a bout of severe diarrhea and repopulate the gut afterward. You can dispute the details. You cannot call it a structure with no described function.

4. There are no gills in a human embryo. What are loosely called gill slits are pharyngeal pouches and arches. In humans these develop into the middle ear cavity and eustachian tube, the tonsils, the thymus, and the parathyroid glands. The name is a nineteenth-century leftover, not a description of the anatomy. A fetus does not recapitulate a fish.

5. The tail is the spine. The embryonic structure is the developing spinal column, which normally shortens as development proceeds. The adult coccyx anchors muscles and ligaments of the pelvic floor. Neither is a discarded leftover, and calling it a tail is a description of appearance rather than of function.

6. This argument keeps losing. Here is the turn. The list of useless organs has shrunk every generation, and the pattern is instructive. The thymus was once considered vestigial and is now known to be the training ground of T cells. The spleen, the tonsils, and the pineal gland were all on someone's list. An argument that keeps retreating is not a strong inference. It is a bet against future research.

7. Common design is a live option. A designer may reuse a good pattern across creatures, exactly as an engineer reuses a proven design. That reading is one Christian option. Other Christians read the same structures as evidence of common descent. The structures alone do not adjudicate between those views, which is why the disagreement is real. Psalm 139:13 says of the unborn, you knitted me together in my mother's womb, and Colossians 1:16 says that by him all things were created. On that reading, reuse of a pattern is artistry rather than accident.

8. Christians genuinely disagree about evolution. BioLogos and Reasons to Believe accept evolutionary common descent and see no conflict with Genesis. The Discovery Institute argues the evidence points to design. All of them affirm that God created (Genesis 1:1). This is a debate inside the church, not a scoreboard where the church has already lost.

9. Granting it would not settle theism. Even if every disputed organ were functionless, that would show something about biology. It would not show that the universe is self-explanatory, that mind arose from matter, or that the resurrection did not happen. The case for God rests on other evidence: the beginning of the universe, fine-tuning, consciousness, and the moral law. Romans 1:20 locates the evidence for God in the created order itself, not in the absence of function in any particular organ.

The examples are weaker than the objection assumes: the appendix has described immune function, the gill slits are pharyngeal arches that build the ear and thymus, and the tail is the spine. Meanwhile the broader question of design is one Christians answer in different ways. Disagreement inside the church is not the same as refutation from outside it.

Sources: Michael Behe, Darwin's Black Box; BioLogos; Reasons to Believe; Discovery Institute; Jonathan Wells.

Related challenges:
• Doesn’t evolution account for the origin and diversity of life on earth, thereby eliminating the need to appeal to God?
• Doesn’t the fossil evidence support the theory of evolution?
• We have SEEN speciation occur in various species of plants. Evolution in action, folks. This should establish beyond all questionable doubt that evolution is a FACT!