Why is the human body so crap except for the liver?

Many people find the human body's design to be inefficient, with most organs decaying or wearing out over time, except for the liver. This observation raises questions about why our body is susceptible to such poor design decisions.

One example is the kidneys. Once fully developed, they begin to deteriorate gradually. Damage from even seemingly harmless actions, like taking too much vitamin D or ibuprofen while dehydrated, can lead to scarring and permanent loss of function. Similarly, gum tissue can recede if not properly cared for, never to return.

The liver, however, behaves quite differently. If injured, it generally heals without scarring. It maintains near full strength as we age and can be partially removed and regenerated in someone else within a few months.

One theory proposes that these fragility issues in most body parts are a deliberate design choice, aimed at preventing cancer. Bacteria, which lack telomeres, do not suffer from this problem. Eukaryotes, like humans, evolved from bacteria and replaced circular DNA with linear DNA. The body's decision to use telomeres, enzymes designed to prevent cancer, is a deliberate design choice, despite its drawbacks.

Telomeres are repetitive sequences at the ends of chromosomes that shorten with each cell division. After around 50-70 divisions, the telomeres are gone, and the cells stop dividing and begin to function poorly. This ticking clock of aging affects many aspects of our body.

Another example is the immune system's tendency to attack transplanted organs, necessitating lifelong immunosuppressants and a high rejection rate within 10 years. Diabetes is another issue, where the immune system may attack the pancreas over time, leading to insulin deficiency and damage to vital organs.

The brain also suffers from a lack of regenerative capacity. Once neurons are lost, they cannot be replaced. Cells in the eyes and neurons accumulate "junk" over time as they divide, further contributing to the ticking clock of aging.

The body's blood vessels can become clogged with plaque, requiring new blood vessel growth. However, the body's default response involves inhibiting this process, leading to slow and inefficient healing.

In conclusion, while the human body's design is far from optimal, several of its shortcomings can be attributed to a deliberate choice to prevent cancer. Evolutionary decisions often prioritize cancer prevention over other potential benefits, and this approach seems to have been the correct one.