Earthworms do not need lungs because they can exchange gases over their body surface. Why won't this work for humans?

The reason why gas exchange over the body surface won't work for humans like it does for earthworms is due to several factors:

1. Size: Humans are much larger than earthworms. The larger an organism, the more cells it has, and therefore the more oxygen it needs to function. The surface area to volume ratio in humans is much smaller than in earthworms, meaning we have less surface area per unit of volume to allow for gas exchange.

2. Complexity: Humans have a much more complex structure than earthworms. Our cells are specialized and organized into tissues, organs, and systems, each with its own specific functions. This complexity requires a more efficient system of gas exchange, which is provided by our respiratory system.

3. Skin: The skin of earthworms is moist, which aids in the exchange of gases. Human skin, on the other hand, is not designed for this purpose. It is relatively thick and covered with a layer of dead cells, which would impede gas exchange.

4. Oxygen Demand: Humans have a higher metabolic rate than earthworms, meaning we require more oxygen to meet our energy needs. Our muscles, brain, and other organs require a constant supply of oxygen, which can only be efficiently delivered by a dedicated respiratory system.

5. Protection: Our lungs are protected inside our body, reducing the risk of damage. If humans relied on their skin for gas exchange, any damage to the skin could potentially be life-threatening.

In summary, while gas exchange over the body surface works for small, simple organisms like earthworms, it is not sufficient for larger, more complex organisms like humans.