Narrative reviewindependent cross-checkabstract checked I-ORG-127 standard review
What the appendix may be for
A review of the function and evolution of the cecal appendix.
Overview
Smith HF. Anat Rec (Hoboken) 2023 · PMID 35363436 · DOI 10.1002/ar.24917
The appendix has evolved many times in mammals and may support gut immunity and gut bacteria.
Does the study support the specific claim? Partly · Methodological quality: low
Plain-language summary
Study explained simply
- What did the researchers want to find out?
Review appendix function and evolution
- How was the study done?
Narrative review
- How many people, animals or samples were studied?
n/a
- What was actually found?
Possible immune and microbial reservoir functions
- How large was the observed effect?
n/a
- What do the results mean in everyday life?
The appendix is probably not useless
- What are the study's limitations?
Narrative, indirect
- What does it say about Elawady's specific claim?
Supports 'not vestigial', not 'harmful to remove'
- Do the results apply to Germany and Europe?
Universal
- What can explicitly not be concluded from this study?
Cannot quantify any harm of removal
Scientific in-depth review
1. Full reference
- Authors
- Smith HF
- Journal
- Anat Rec (Hoboken)
- Year
- 2023
- Identifier
- PMID 35363436 DOI 10.1002/ar.24917
- Verification
- verified – PubMed efetch 2026-10-26; Crossref works API 2026-10-26
- Retracted
- no
- Corrections
- none
- Extent checked
- abstract only
- Conflicts of interest and funding
Not stated in abstract.
2. Research question
Current understanding of the pathophysiology, evolution and possible functions of the appendix.
3. Study design and population
- Study design
- Narrative review – Narrative review of human appendix function and comparative evolution
- Population
Mammals including humans
- Country
Not applicable
- Period
Not stated
- Sample size
Not applicable
- Inclusion and exclusion criteria
Not systematic
4. Methods and endpoints
- Exposure / intervention
Appendix presence
- Comparator
Species without appendix
- Endpoints
Function, evolution
- Statistical methods
Phylogenetic mapping (summarised)
5. Actual results
- Results
Abstract: recent studies indicate that the appendix may have protective functions (immune response, re-inoculating the gut with commensal bacteria after illness); the cecal appendix evolved independently numerous times in mammals, more than expected by chance, suggesting it is adaptively advantageous; no single driving ecological factor identified.
- Absolute risks
Not applicable
- Authors' conclusion
The appendix has a complex evolutionary history and possible protective functions.
6. Strengths
- Comparative evolutionary evidence
7. Weaknesses
- Narrative review
- Human functional evidence largely indirect
8. Risk of bias
- Orienting tool
- none applicable
- Type of assessment
- simplified assessment (abstract only)
- Full formal assessment
- no
- Overall risk of bias
- not assessable
- Rationale
Narrative review.
9. Assessment of the statistical interpretation
Not applicable.
10. Relevance to the specific claim
Supports the general statement that the appendix is not simply vestigial.
11. Independent contrary findings
Evidence for clinically relevant loss of function after appendectomy in healthy people is weak (Naga 2023, I-ORG-128).
12. Transferability to Germany and Europe
Universal biology.
13. Overall methodological judgement
Supports 'not vestigial' as a scientific view; does not show harm from appendectomy.
| Multidimensional assessment | |
|---|---|
| Authenticity of the source | verified |
| Methodological quality | low |
| Risk of bias | not assessable |
| Precision of results | not applicable |
| Directness | indirect |
| Reproducibility | unknown |
| Consistency with the overall evidence | consistent |
| Regional transferability | high |
| Adequacy of the interpretation (by the archive) | not applicable |
14. Open questions
Human functional studies.