why do humans need to eat many different kind of foods to get their vitamins etc but large animals like cows only need grass to survive?
In: Biology
Ruminants like cows are able to extract more nutrients from vegetation than we are, due to their specially adapted digestive system and gut flora.
Ruminants ferment food in their four-chambered stomach over an extended period, which enables their gut bacteria to break down complex carbohydrates, proteins, fiber, which in turn synthesize their own nutrients that the host can absorb.
Additionally, ruminants will consume animal bones in order to obtain phosphate and calcium if they’re not able to obtain it elsewhere in their diet.
In addition to the ‘efficiently breaking down grass’ thing, and the ‘they eat a variety of plants’ thing, there’s also the fact that species typically evolve the ability to make vitamins that they can’t get easily in their diet. For example, humans make vitamin D because there aren’t many food sources of it, but we can’t make vitamin C, but can find it in food. But other species can make their own vitamin C.
It’s a trade off between needing to find a variety of food and not needing the cellular machines to make more stuff.
Wild deer sometimes eat dirt, well if they can they find a salt lick. But they still go looking for minerals not found in the plants they eat. They also occasionally munch baby birds. Possibly other small wildlife, but I know about the birds. It’s a bit like the way a dog or cat sometimes eats grass.
Part of it is they’re bulk feeders. Cows will eat 20+ pounds of food a day, up to nearly 40 lbs for meat cows being fed for fast weight gain. They spend a huge portion of their waking hours just eating, with an otherwise sedentary life.
From this enormous food intake they can extract a decent quantity of nutrients that are relatively scarce in their diet. For more complex nutrients they basically carry around a biological factory in their gut to process the vegetable matter into all the proteins they need from their diet.
1. Different animal’s digestive systems work very differently
2. You could survive on only potatoes, you would just be far less healthy and have a reduced lifespan, like many animals in the wild vs those in captivity.
I’m not going to try to explain why humans and animals eat different foods because I don’t know enough about it myself.
What I can tell you is that humans *can* survive on extremely limited diets. They just won’t be as healthy as someone who eats different kinds of foods.
At least one thing is that we can’t make vitamin C ourselves, which is a negative mutation we have compared to other animals.
Because it is the most efficient. We can get all the nutrients we need in about an hour over all and spend the rest of the time doing stuff.
Carnivores spend 80% of their day sleeping, and herbivores spend 80% of their day eating. We spend 30% of our day sleeping and <10% eating. It’s the best of both worlds.
Fun fact: We actually still have most of the genes required to synthesize vitamins, such as the gene to synthesize vitamin C which dogs and cats possess, but it is deactivated.
When we started living arboreal lifestyles and consuming a lot of fruit, it was no longer evolutionary preferential to synthesize our own vitamin C- it takes much less energy to absorb it from food, where the plants have already expended the energy to synthesize it- and therefore the gene has gradually grown redundant in chimps and eventually humans.
The same has occurred for many other aspects of our genes. Any expense of energy which can be avoided is generally selected against, because individuals who could survive longer with less food were more likely to survive periods of scarcity and thus produce offspring.
Others have explained it well, but another fact about many animals that we think of as herbivores(cows, deer, squirrels) will commonly eat meat if it’s available! Cows and deer have both been seen munching on baby birds in low nests, as well as chewing on bones from carcasses
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