---
title: 'Why Don''t Our Bones Keep Growing Forever?'
source: 'https://youtube.com/watch?v=yOUnIhrRfq0'
video_id: 'yOUnIhrRfq0'
date: 2026-07-28
duration_sec: 192
channel: 'MinuteEarth'
---

# Why Don't Our Bones Keep Growing Forever?

> Source: [Why Don't Our Bones Keep Growing Forever?](https://youtube.com/watch?v=yOUnIhrRfq0)

## Summary

Humans stop growing taller around age 20, while most vertebrates grow throughout their lives. This video explains the biological mechanisms behind growth plates and the metabolic trade-offs that limit human height, contrasting us with animals like alligators.

### Key Points

- **Growth Differences** [00:00] — Most vertebrates grow bigger throughout life, but humans stop growing taller by around age 20.
- **Growth Plates** [00:26] — Bones have growth plates—layers of cells that divide and become new bone. In alligators, these remain active; in humans, they harden after puberty.
- **Hormonal Hardening** [00:53] — After puberty, hormones cause growth plates to harden permanently, stopping longitudinal bone growth.
- **Exception: Robert Wadlow** [01:06] — People like Robert Wadlow grew to 9 feet tall because a condition prevented growth plate hardening.
- **Metabolic Constraints** [01:22] — Humans have fast metabolisms that produce heat. As size increases, volume (heat production) grows faster than surface area (heat dissipation), risking overheating.
- **Alligators' Advantage** [01:55] — Alligators have slow metabolisms, so they don't overheat even when large, allowing continuous growth.
- **Conclusion** [02:22] — Humans stop growing to avoid overheating; while being larger has benefits, our metabolism limits size.
- **Sponsor: Tab for a Cause** [02:35] — The video is sponsored by Tab for a Cause, a browser extension that raises money for charity (e.g., animal welfare) with each new tab.

### Conclusion

Human growth stops due to metabolic constraints—our fast metabolism generates excess heat that would be dangerous if we grew larger. In contrast, animals like alligators with slow metabolisms can grow indefinitely.

## Transcript

almost all vertebrates– get  bigger throughout their lives; Then, there are humans, who, by the age of 20 or  so, just stop getting bigger… or at least taller.
Hi, I'm Cameron, and this is MinuteEarth. growing –like a lot of other questions  about the world around us– in two ways.
what actually stops our bones from  getting longer at some critical moment? why do humans stop growing at a certain  point, while other animals don’t?
Many bones have special layers of cells  on each end known as "growth plates";   these cells are constantly dividing  and turning into brand-new bone. And for the alligator, that growth  continues throughout its life.
But in humans, once puberty is complete,  our bodies release hormones that harden   our growth plates permanently, turning  them into "no-more-growth" plates. imbalance– will block this  normal process from happening;
like nine-foot-tall Robert Wadlow,  reach their towering heights. the hardening of your growth plates  means you can’t get any taller. Now, here's where –if you're thinking what  I'm thinking– you're contemplating that bigger  
question of why this whole growth-stopping  process happens at all in us humans. and birds– are energy-hungry critters. Our fast metabolisms allow us to  run –or swim or fly– long distances,  
but they require a lot of energy to  sustain, even when we’re at rest. And if you recall, as an animal grows, its volume,  and therefore the amount of heat it produces,   increases much faster than its surface area does  – surface that's needed to vent that heat outward.
sense that there’s a biological  process that limits our growth. much slower metabolisms that don’t  burn much energy most of the time.
Even as they grow bigger – and their  relative surface area decreases – they’re   And since being big does confer a lot of benefits,   they might as well keep on  getting bigger throughout life.
After all, it would be nice to be  able to reach the highest fruit   Unfortunately, we just can't take the heat.
it’s the ridiculous amount of browser  tabs I have open at any one time. But that’s alright because I use Tab  for a Cause, a simple browser extension   that lets users raise money for charity  for free just by opening browser tabs.
to help end animal cruelty in factory farms. and every tab you open will raise money that  will go toward improving the lives of animals.