Why Do Some Plants Make It So Easy To Eat Them?
There are a lot of things out there invested in your existence. Most of them only like you for your poop.
Steps in Successfully Eating Grain
First, you must harvest the grain. Cut the stalks just above ground, tie them into bundles to make carrying them easy, and let them dry.
Once dry, beat the stalks with a wooden dowel to release the grain. Collect these seeds.
Separate the grain from the chaff, using a fan, or water, or your own two hands to separate the covering from the seed.
Mill the grain into a fine powder, fit for baking, or soak it for several days and allow it to sprout, letting bacteria breaking down some of the grain’s more potent molecules.
At this point the grain can be eaten raw, used for baking, or consumed in any number of ways.
Steps in Successfully Eating an Apple
First, you must pick the apple. Reach up and grab the apple on the tree and twist gently until the stem separates from the branch.
Eat the apple.
At a first glance, it seems like grains have a lot smarter strategy in this arena (and it seems kinda crazy that more than half of human calories come from cereal crops). But typically most organisms have reasons to look and operate the way they do. So the abundance of easily-eaten fruits and berries in our world begs the question:
Why Do Some Plants Make It So Easy To Eat Them?
And it turns out, there are a few reasons.
1. Your Mother’s Favorite Boogeyman: GMOs
The first and most obvious answer is that, for most common fruits in our lives, the plants didn’t develop that way on their own. Even before we learned to edit genomes by hand, humans were still directing the evolution of other species, selectively breeding crops over thousands of years until they turned into easily eaten, sweet sacks of nutrients for us to survive on. The classic example here is the wild banana, which is nearly — but not entirely — unrecognizable compared to a modern Cavendish:
Wild bananas — much smaller and with a lot more seeds than our domestic varieties. Image copyright CC-BY-NC 2.0 VitaminGreen.
But that said, even a wild banana is still a lot more user-friendly than a stalk of wheat. The instructions still look pretty similar to a modern-day apple:
Steps in Successfully Eating a Wild Banana
Pick the banana. You may wish to pull the individual banana, twisting until the stem disconnects, or use a blade to sever the entire bunch.
Peel and eat the banana.
Spit out seeds as necessary.
Our essential question is still unanswered. Even before humans started directing, some plants were much easier to eat than others. What gives?
2. We’re All In This Together: Mutual Benefit
Another explanation comes from the fact that you’re not the only one who benefits when you eat a fruit. Sure, you get all sorts of nutrients and calories to keep you upright and walking, but in the middle of that little ball of energy lie the plant’s most precious cargo: seeds, usually surrounded by something your body can’t even digest. That way, when you go to, ehm, release all the food mass left over past the large intestine, the seeds of whatever you’ve been eating get placed right in a nutrient-rich pile of manure — by which point you’ve hopefully walked far enough away that the new seedlings don’t have to compete with Mom for the light. Even just tossing the seeds as you walk (which you should really stop doing, by the way) tends to disperse those heavy seeds further than the plant can get them by itself.
This is the second most talked-about explanation for why some fruits are so edible — heavier seeds lead to more competitive seedlings, but make it a whole lot harder for the parent to disperse them on their own. So the plant strikes a bargain with the animal kingdom: if the plant agrees to give up some nutrients and calories, the animal will spread the seeds further than the plant could manage on its own. And as just a bit of insurance, the plant does everything in its power to make sure the seeds survive the travel — this is why apples, pears, plums, peaches, and cherries all have cyanide in their seeds, and one of the reasons seeds are so much tougher and less appetizing than the rest of the fruit. The plant is just making sure you stick to your end of the bargain.
This makes a lot of sense from an evolutionary perspective. Plants compete with one another to offer the most appealing fruits, which animals will then happily eat and spread. But it’s a certain ego that makes us think the adaptive pressure is entirely on the plant — it’s worth flipping our question around, and asking:
3. Why Do Some Animals Make It So Easy To Use Them For Seed Dispersal?
Balanites wilsoniana is a tropical species of tree dispersed only by elephants, whose guts provide the perfect environment to ensure that the seeds will germinate once deposited far away from home. Similarly, Trewia nudiflora is a common tree along riverbanks whose fruit is only eaten by the greater one-horned Asian rhinoceros, and is largely restricted to areas that these vulnerable animals still roam. This is a common pattern among trees with larger fruit — only a handful of species will be properly adapted to eat and digest the fruit, while most other species in the region avoid it altogether.
By forming these highly specialized partnerships, the plant is able to fine-tune its offering to that which will likely appease its target species the most. The nutrient and energy content of fruit varies from species to species, but can evolve to target a specific group of species, sacrificing only the necessary amount of nutrients to catch a species’ eye. Get the species hooked on what you have to offer, and you’ll have easy access to all the seed dispersal you could need. Do it well enough and you can even direct animal evolution — for instance, even color vision may have developed to help identify a species’ preferred food supply.
A Word of Caution (If You’re a Plant)
Of course, it’s easy to go too far down this road. If a plant develops so that it’s entirely reliant on a single species for seed dispersal, it can wind up having a single point of failure for its entire evolutionary lineage — if that animal disappears, it’ll have a much harder time not going extinct itself. And the world is littered with plant species who are living out their twilight years having lost this exact bet — Ginko biloba, avocados, and paw paws all dutifully put out their anachronistic fruits year after year, waiting on their dispersal agents who will never come again. We can even guess at extinct animal lineages by looking at what fruit doesn’t have a corresponding animal species.
Still, avocados still exist, as do Gingko and paw paw trees. In this case, it seems like these plant species got lucky — the two legged monkey that wiped out their original dispersal agents just so happened to enjoy eating the fruit themselves, or perhaps liked planting the tree for ornamental reasons. As such, these species have been able to survive long past the extinction of their partner animals — but history is covered in species which did not get so lucky, and died out quietly once they could no longer be spread.
Nature demands the same of all: Adapt, or die. Only a few species manage to take the first option.
Coda
Which brings us back to our original question:
Why Do Some Plants Make It So Easy To Eat Them?
And the answer is, as ever, it depends. Some plants are competing for us to pick them, to do their dirty work and spread their seeds across the land. Some plants we’ve had to help along the way, picking only the most appealing individuals to survive and create the next generation. And some plants have gone further and actually selected us, decided that we were their best chance at spreading throughout the landscape, and trained us to seek out their fruit.
In all circumstances, both parties only do what they see as being in their own best interest: the plant does the least amount possible to see its seeds dispersed, the animal seeks out the most nutrient rich food available to hand. So long as it helps them survive, everyone keeps coming back to the table. And so the species might survive for one more generation on this cold, wet rock of ours.