A few days ago my teacher brought up Henrietta Lacks during my science class. We discussed her cells (referred to as HeLa cells), which had a remarkable trait of immortality. HeLa cells didn’t die, causing them to replicate and form large tissues.
This discussion brought up a lot of questions for me, both ethical and scientific. The one that I am writing about today has to do with the neuron. While the neuron isn’t immortal, it is meant to live a very long lifespan compared to other cells such as skin or liver cells, around 80 years, or an average person’s lifespan. However unlike HeLa cells, neurons don’t typically replicate, which leads to damaged, lost, or dead tissue in the brain never getting replaced.
This really surprised me. I assumed the brain, like most other organs in the body, would greatly benefit from constant renewal. But the more I thought about it, the less obvious that idea became.
Neurons aren’t just individual cells performing isolated functions. They exist as part of highly specific networks, where each pathway between them contributes to how information is stored and processed. Memories, learned skills, and even aspects of personality are tied to these connections.
If neurons were constantly dividing and replacing themselves, those connections wouldn’t stay stable for long. Even small changes in structure could alter how information is represented. Instead of preserving knowledge, the brain might continuously overwrite or distort it. In that sense, replication could become a liability rather than a benefit.
Cells like those from Henrietta Lacks survive through constant division. That works well in contexts where growth is the goal, but it also introduces randomness. New cells are not perfect copies in function, and their integration into existing systems isn’t guaranteed to be precise. In something like the brain, where function depends on exact organization, even slight inconsistencies could have large effects.
Rather than optimizing for renewal and growth, the brain optimizes for stability. Neurons are maintained for as long as possible, preserving the structure of the networks they form. Instead of replacing parts, the brain adjusts by strengthening or weakening connections between existing neurons, a process that is both slower and more controlled.
There are some exceptions to this. In certain regions, like the hippocampus, new neurons can still form through a process called neurogenesis. But even there, this process is limited and tightly regulated, which reinforces the idea that adding new cells must be done carefully to avoid disrupting existing circuits.
The same property that makes HeLa cells powerful, their ability to constantly renew themselves, might make them incompatible with the level of precision required for stable thought.