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Mar 4 2009
Evolution and Edible Fruit

One of the e-mails we received after our billboard went up was by a person who was trying to offer evidence that the world was created by an intelligent and benevolent supernatural being. One of his arguments, which I had not specifically heard before, had to do with the existence of edible fruit. In particular, he suggested that fruit was healthy and delicious and -- so far as he knew -- never poisonous. And, he asked how this could be possible without an "intelligent designer".

This is an interesting question, and so I gave it some thought.

The first thing to point out is that there are poisonous fruits. For instance, the holly berry and mistletoe (both associated with Christmas, for some reason) have poison berries. The Mayapple, Castor Bean, Jerusalem Cherry and Deadly Nightshade (a close relative of the tomato) are all also poisonous. There are even plants which have poisonous parts even though we eat other parts. The fruit that grows around an almond is poisonous, as are the seeds of peaches and apples. (For more, see here and here.)

However, that is not the really interesting part of the question. The interesting thing is to think about why there are so many fruits (a whole aisle of them at the supermarket!) that we can eat. If I could not explain that without reference to the supernatural, then I would indeed have to reconsider my worldview.

The fact is, I can think of three natural explanations for the prevalence of edible fruit in the world today, and they seem to be in very good agreement with all of the evidence.

First, we should note that some things are poisonous to some creatures but not to others. For instance, as we all know, cocoa is poisonous to dogs, but not to humans. Now, suppose that in the early history of humanity the only fruits around were ones that were poisonous for them to eat. There would be strong evolutionary pressure then for them to develop an immunity to the poison. In other words, if most of the humans could not eat the fruit but a small handful with a mutation could, then that small group would be able to survive better since they had a great deal more to eat and very soon they would be in the majority.

The second naturalistic explanation for edible fruit involves the fruit changing so that animals can eat it. One has to wonder why fruit exists at all. According to the fossil record, there were many millions of years of plants without flowers or fruit. What advantages do the fruits offer the plants? They can protect and fertilize the seeds, but they offer another advantage that plants otherwise lack: mobility. If a plant can spread its seeds far away, that will increase its chances of successfully reproducing and spreading. However, as you may have noticed, plants don't walk. One of the ways they have evolved to spread seeds is to make them light enough to blow away (like dandelions), but another is to have them ingested by an animal and then spread through its feces. Think of it this way, if there were two identical plants that each had fruits with seeds in them, but one was poisonous and the other wasn't, what would happen? The plant with the poison fruit might have some offspring growing right near it (competing for resources), but the one with the edible fruit will have its seeds carried far away by animals and (forgive me) fertilized by their feces. Here is a relevant quote from Wikipedia:

Seed dispersal via ingestion by animals, or endozoochory, is the dispersal mechanism for most tree species [10]. Endozoochory is generally a coevolved mutualistic relationship in which a plant surrounds seeds with an edible, nutritious fruit as a reward to frugivorous animals that consume it. Birds and mammals are the most important seed dispersers, but a wide variety of other animals, including turtles and fish, can transport viable seeds[11]. The exact percentage of tree species dispersed by endozoochory varies between habitats, but can range to over 90% in some tropical rainforests [10]. Seed dispersal by animals in tropical rainforests has received much attention, and this interaction is considered an important force shaping the ecology and evolution of vertebrate and tree populations [12]. In the tropics, large animal seed dispersers (such as tapirs, chimpanzees and hornbills) may disperse large seeds with few other seed dispersal agents. The extinction of these large frugivores from poaching and habitat loss may have negative effects on the tree populations that depend on them for seed dispersal [13].

The explanations offered so far above do not depend on any sort of intelligence or understanding. If there was an island with a variety of creatures and plants on it, if some of those plants had fruits edible to some of the creatures, the creatures who could not eat the plants and the plants which did not have edible fruit would both be at a disadvantage. So, after a while there would be lots of creatures who can eat fruit and fruit that is edible to creatures even if neither the creatures nor the plants understand what is happening. This is a key aspect of evolution which is not generally appreciated by its critics: the end result of natural selection can look like "intelligent design" without the need for any intelligence.

The third of my naturalistic explanations for the prevalence of edible fruit, however, does depend on intelligence...just not supernatural intelligence. The fact is that we humans are largely responsible for the variety of edible fruits in the world. Consider, for example, the apple tree. You can see lots of different varieties of apples in the grocery store (red delicious, pink lady, gala, granny smith, etc.) but these did not all exist somewhere in nature (or the Garden of Eden) until we bred them. I don't think that creating new breeds is something controversial to it? Take a look at the American Kennel Club. They make no secret of the fact that we have created the different breeds of dogs by selection. In fact, the same is true of fruits. Consider:

The Crab-tree or Wild Apple (Pyrus malus), is native to Britain and is the wild ancestor of all the cultivated varieties of apple trees.

In other words, if it wasn't for us, then there would only be the small, extremely tart "crab apple" growing in Britain. The fact that there are bigger and sweeter varieties growing all around the world is due to our efforts.

So, to summarize, I really think that it would be surprising if there were not a lot of edible fruit in the world. Between the evolutionary pressure on creatures to develop tolerance to the toxins in the plants that grow around them, the advantage to plants in producing edible fruits, and the efforts of thousands of years of human farmers in selecting and propagating the seeds of any plants that do make edible fruits, it would take a supernatural power to prevent them from existing rather than to explain why they do.

Mar 10 2009
Re: Evolution and Edible Fruit

There's always the monkey clause.

Monkeys know how to eat a banana better then humans do.

from the bottom peel upward - stem on top - reason: the stringy part of the banana generally runs along the lenght of the banana, but comes off with the skin if opened upside down.

Monkeys figured this out. most humans have not.

So, do monkeys know better?

Mar 18 2009
Re: Evolution and Edible Fruit

Monkey Claus would make a great mascot for the winter solstice.'re probably just being silly, but...since banana peels contain important trace elements which we humans can get if we peel from the top down and eat some of the stringy stuff, maybe we're the smarter ones. Or maybe it's just dumb luck. And, maybe the monkeys peel from the bottom because it's easier for them due to their hand morphology or to the condition of their bananas opposed to our cultivated grocery store bananas. They don't leave the skin on to keep their hands clean like we do, but they do throw their poo at each other. Hmmm. Maybe their palates are more sensitive than humans' and the bottom of the banana tastes better. Is this is a digression or a hypothesis? Next time you're at the zoo take two bowls of mashed banana, one made from the top of the banana and one made from the bottom of the banana, and see if your monkey has a preference. That might shed a little light on the subject.

Y'know some humans open their beers from the bottom and drink from that end of the can because it enables them to consume and feel the effects of alcohol faster. Maybe they know better. Or, maybe the bottom of the beer tastes better. Hmmm. Now, that's an experiment I can do.

Alex, I have to give you credit for presenting a nice objective argument. I have to admit that I'm way too intellectually lazy to give it much thought and would have just dismissed the guy as silly.

Mar 28 2010
Re: Evolution and Edible Fruit

Garfield's Rule: avoid fruits and nuts-- you are what you eat!

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