Why can’t human eat grass?

Can we eat grass? We all know that our ancestors have practiced nomadic grazing in the past. It was a practice across the origins of human civilization. They brought herds of livestock from pasture to pasture. Then the meat from livestock was consumed as a vital source of nutrients. But one question arises. Why don’t our ancestors eat the grass directly? Why can’t we survive on eating grass? Why do we have to rely on the animals to digest the grass and transform the energy into more absorbable form for our consumption? Would it be more efficient if we can eat grass? Why aren’t we evolve to digest grass?

In fact, the question that why human can’t eat grass is not a rigidly posed question. How do we define grass? In strict biological sense, wheat, rice, barley, corn and bamboo are all grass, even though their appearance may not fit into our perceived image of grass. We consume their seeds. For example, when we eat bread or rice, we are surviving on grass but the seeds of it. So it is true that human can eat grass, but the seeds of grass. But our modern technologies help us extract the grain from the seeds. If you see seed-eating birds, they do the same with their thick beak. It is the same principle that a threshing machine works, removing the grain from the hulks.

To be more specific, we don’t eat the leaves of grass, which are the green parts constantly chewed by the livestock. In fact, when you are hungry and there is no sign of food but only grass beside you, the leaves of grass are surely an option. But inside the leaves, there are too little nutrients. Our digestive system has to work a long time in order to extract the feeble amount of nutrient from grass. More importantly, they do not taste good. So, over the years, humans learn to choose not to eat grass when presented the opportunity.

But grass knows that animals are eating it. So grass has already evolved and built their own defense mechanisms against their most direct enemy, the herbivores. There has been ongoing battle between the digestive system of herbivores and the defensive mechanisms of grass. For instance, the cells of the grass are becoming harder and harder to digest. Yet, throughout the evolution, animals have developed specialized multiple-stage digestive system to breakdown the cells and extract energies from grass. But we, human, have chosen not to compete with the grass. Yes, we gave up.

Therefore, the next time you are asked the question, why can’t we eat grass? Please dodge the question by saying that we eat the seeds of grass every day. But we do not eat the leaves of the grass because our bodies can only gain so little given the hard work.