Quirks of Human Anatomy

Lewis Held's "Quirks of Human Anatomy" meticulously catalogues several suboptimal human anatomical features, presenting them not as defects but as historical artifacts of our evolutionary journey. The piece highlights how these quirks, while sometimes inconvenient or even dangerous, reveal the improvisational nature of evolution, which often builds upon existing structures rather than starting anew.

• Ear Wiggling Muscles: Vestigial muscles that serve no apparent function beyond a party trick.
• Inverted Retina & Blind Spot: Photoreceptors are behind ganglion cells, leading to a 'blind spot' where the optic nerve exits. This geometry is traced back to a protochordate ancestor whose superficial nerve net was internalized.
• Crowded Teeth: Modern humans often have issues with wisdom teeth due to the evolutionary shortening of our jaw.
• Branchial Arches: Embryonic structures that are remnants of our fish ancestors.
• Male Nipples: Useless in males, a side effect of shared developmental pathways.
• Choking Hazard: The shared pathway for air and food, a result of lungs evolving from the eating tube, makes choking a risk. Babies and many mammals avoid this due to a higher larynx.
• Painful Childbirth: The tight fit and necessary rotation of a baby's head through the human pelvis is a difficult evolutionary compromise, contrasting with the easier exits in other species (and the extreme case of the spotted hyena).
• Back Pain: The spine's sinusoidal shape contributes to lumbar strains and herniated disks.
• Long Vas Deferens: A circuitous route for sperm delivery, much longer than necessary due to evolutionary history.
• Prostate Obstruction: The urethra passes through the prostate, risking strangulation if the gland enlarges.
• May-Thurner Syndrome: An asymmetrical compression of the left iliac vein due to its anatomical relationship with the abdominal aorta.
• Ectopic Pregnancy: The gap between the ovary and oviduct can lead to dangerous 'tubal' pregnancies if an embryo implants prematurely.

The article also delves into the evolutionary history of the eye, comparing human 'simple' eyes with insect 'compound' eyes, and reflecting on how even seemingly perfect biological systems are the result of countless incremental adaptations rather than perfect design. The author uses references from various scientific works, emphasizing the 'tinkering' aspect of evolution as described by François Jacob.

Ultimately, the piece illustrates that our bodies are a living museum of evolutionary compromises, full of 'good enough' solutions that have persisted despite their imperfections, a testament to the powerful, yet often non-optimal, process of natural selection.