When certain aquatic plants keep growing throughout their life, then why do we terrestrial animals stop growing? Well, a simple explanation is that that all animals, including humans, have evolved such that they stop growing at a size that balances energy efficiency and their competitive needs as they struggle to survive.
In humans, genes determine the growth pattern and height that one attains. Growth is said to occur when cells called chondroblasts multiply, adding cartilage to the ends of bones. Cells called osteoblasts then deposit calcium and other minerals in the cartilage and turn it into new bone tissue. As the deposition of calcium and minerals goes on, bones become longer and you grow taller. Toward the end of puberty, your body produces lots of oestrogen and this inhibits chondroblast proliferation thus slowing down the addition of new cartilage to the ends of your bones. When all the cartilage in the active growth area is calcified, you stop growing.
The overproduction or underproduction of certain hormones (bio-chemicals released in our body) or the inability to respond to them can affect growth, making it above or below normal. Gigantism is caused by the overproduction of the pituitary growth hormone, whereas severe short stature is often caused by the bodyâ€™s inability to respond to this and other growth hormones.
Another interesting theory to explain this issue is that terrestrial animals have to support their weight without any help. Therefore, we have been designed to stop growing to protect our bodies from becoming bigger than we can manage.
According to space researchers, if you travel into space, you will â€œgrowâ€, irrespective of your age. Although the effect is temporary, you can actually grow by as much as eight centimetres while in orbit, they say. This is due to reduced gravitational force acting on your body. As a result, the spinal column stretches out a bit thus making one taller. This phenomenon is also visible when you are asleep. If you sleep horizontally, you will actually be a little taller in the morning since gravity is unable to compress your spinal column until you stand up.