Fruit Trees

March 24, 2004 10:42 PM

I've always kind of wondered this. I don't know if it's a metaphysical question, an evolution question or just a childish question, but why exactly are there fruit trees? Has anyone seen a definitive answer to this. Does it seem weird that a tree would produce fruit just so animals can come and steal it? Do fruit trees benefit from producing fruit (like I understand how the leaves come into play)? I feel like a little kid asking this, but does anyone got an answer?
posted by Slimemonster to science & nature (28 comments total)

Animals eat the fruit, and poop out the seeds somewhere else. Where they grow into new fruit trees.

Circle of life, man.
posted by Guy Smiley at 10:44 PM on March 24, 2004

A rare thing indeed... a science question I could answer and someone beat me to it.
posted by dobbs at 10:48 PM on March 24, 2004

And there is even a type of tree that has pine cone type things that only open when there is a forest fire, so natural forest fires actually help to distribute the seeds. Mother nature is so cool, it's got plans for everything. It's like the world is a living organism, you can hear it's heartbeat in the wind, and feel its warmth to the core. And its blood is the oil, but we take so much of its blood that I hope it does not die. Why do you think that there are oil wells that are filling back up for no reason? Because it is alive. And there is a natural cycle where humans produce carbon dioxide and trees and rocks and the oceans absorb it, but we are producing so much carbon dioxide now that it is off the charts and I fear for my children because we're throwing the system of life out of wack and there is going to be terrible consequences. Rapid climate changes that will cause war and famine throughout the world. You wait and see, the collapse of all of human society is soon, and evolution will again take over, and perhaps another society will develop and find a way off of this planet before the Sun dies in 5 billion years.
posted by banished at 11:33 PM on March 24, 2004

Besides the animal poop thing, fruit falls from trees, rolls, decomposes into the ground and the seeds grow.

Also, plants with burrs reproduce when their burrs get tangled in the fur of a passing animal (or your sleeve), carried a distance and dropped. The seeds grow where they land.
posted by tomorama at 12:53 AM on March 25, 2004

wow, that seems so...sensical now that you guys mention it. You're scaring me, banished.
posted by Slimemonster at 1:32 AM on March 25, 2004

Scares me too, but there's more than a little sympathy to what he said coming from me.
posted by dash_slot- at 4:13 AM on March 25, 2004

The real question is: why does fruit go to all the trouble of making trees to hang from?
posted by signal at 5:25 AM on March 25, 2004

What's the evolutionary advantage, from the apple tree's point of view, in having the seeds be aboard a yummy treat? Plenty of plant species have thrived for millennia with boring seeds that just fall to the ground, or that are eaten and distributed by animals despite not being plump and juicy. What's up with the fruity goodness?
posted by stupidsexyFlanders at 6:14 AM on March 25, 2004

I don't think there's any straightforward answer to that, stupidsexyFlanders, although we can speculate. My own feeling is trees can employ - simplistically speaking - two different strategies for seed propagation. They can either use a scattergun approach and produce tens of thousands of small seeds that individually have a very small chance of landing intact in a good location, or they can use a more concentrated approach by producing a smaller number of higher-resource seeds (e.g. apples) that have a higher chance of successfully growing into a new tree by virtue of being yummy to eat and thus sure to be picked up by some far-roving animal. Of course, in the real world these strategies are merely two ends of a spectrum. The point is that while there are definite benefits to having fruity goodness, there are other ways to do it as well.
posted by adrianhon at 6:29 AM on March 25, 2004

If I remember correctly from a botany class, some fruit trees have males and females, and need the cross gender pollination in order to bare fruit. Sooo...whoever gets around, makes a round juicy fruit.

Sir David Attenborough has some wonderful programs discussing why plants do what they do. Probably available from a PBS store or the BBC?

BTW, a variant of mistletoe has a seed the size of an almond, and the bird who eats the fruit (the only animal to eat it), poops the seed out on a branch of a parasitic tree, where the seed attaches itself and grows into a new mistletoe plant. What's amazing is the size of the bird and the size of the seed aren't too different.


posted by grefo at 6:30 AM on March 25, 2004

Simply because it can, that's why. Some genetic material nature has found ways of recombining via mammalian sex, and some via pollination, and some in other ways (bacterial division of cells, say). Some of the successful methods involve gestation - works well for mammals. Nature simply has found multiple methods of nurturing DNA - and some of it's ways are very specific (some fruit will not germinate unless passed through the stomach of a certain animal, for instance).

I always thought that a tasty snack surrounding the seed (like an apple does) would increase the likelihood of consumption by said animal, and the deposition into fertiliser.

Or, what Guy Smiley said in the first comment.
And, what adrianhon said so succinctly just now.
posted by dash_slot- at 6:31 AM on March 25, 2004

Right on banished. Feel the rhythm.
posted by tr33hggr at 6:37 AM on March 25, 2004

grefo, you're thinking of David Attenborough's The Private Life of Plants, which is indeed excellent. Amazon has it. Cheap asian "releases" are on eBay all the time. I picked up the 10 DVD box set for $10 as I already had it on a legit VHS copy and didn't want to spend big bucks just because my vcr died.
posted by dobbs at 7:28 AM on March 25, 2004

The trees don't "employ strategies" to distribute their seeds...once upon a time, a tree had a genetic mutation that caused a fruit to grow around its seeds. Some animals ate it and liked it, and carried the seeds to where they pooped. A new tree with the same mutation then grew there, where animals again discovered the tasty fruit. And so on and so forth. As the fruit continued to mutate, the animals would eat the ones that tasted best, so the new ones that grew would slowly start testing better and better.

Just because other trees don't grow fruit and survive doesn't mean other ways to distribute seeds won't evolve. The appearance of fruit bearing trees today is a consequence of the fact that the fruit did help to spread seeds -- new methods of survival need not arise as a "response" to some envornmental hardship.
posted by mfbridges at 8:14 AM on March 25, 2004

Another aspect of this whole seed thing: some plants grow better when their seeds are spread over a wider area, instead of clustered close by. If offspring are competing for the same nutrients, the species overall loses. Using a variety of methods to spread seeds over a wider area increases the ability of the species to thrive. Fruit helps in this way.

My favourite is peppers. The capsicum makes it unappetizing to unappreciative mammals (appreciative humans excluded, of course), so those animals avoid eating their fruit and pooping out the seeds nearby. But birds aren't affected by the hot stuff and gobble up peppers, spreading the seeds over a much wider area.

Nature is just one big cool place with innovative answers to everything. Nature always finds a way.
posted by GhostintheMachine at 8:29 AM on March 25, 2004

Of course they don't employ strategies in the literal sense. It's not as if I'm saying that trees go and have a meetup and say, "Well folks, it looks like the scattergun strategy didn't work with our generation, so why don't we give the apples a go next time around, eh?" However, on higher levels the word 'strategy' is a useful shorthand for talking about how an organism goes about solving a problem, i.e. reproducing, even if there is no intelligence behind it. Similarly, people use the term 'evolutionary stable strategy' even though there is no-one actually *employing* a strategy.
posted by adrianhon at 8:30 AM on March 25, 2004

It's not as if I'm saying that trees go and have a meetup and say, "Well folks, it looks like the scattergun strategy didn't work with our generation, so why don't we give the apples a go next time around, eh?"

how do you know, hey?
posted by Pericles at 9:28 AM on March 25, 2004

The following is my attempt to condense all of evolutionary biology into a few short and simple paragraphs.

The driving force for evolution, and all life, is the information contained within the genes. Information not only wants to be free, it wants to propagate itself.

Those genes that contain information that better propagates are genes that will come to dominate the scene. This is evolution in its raw form: the distribution of winning information.

From this point of view, then, trees are not actors in this play. They are passive mechanisms controlled by the genes.

One should not be asking how such-and-such benefits the tree. The tree is irrelevant except insofar as it serves to distribute the genes. If the genes were to mutate in such a way as to permit a better way to propagate themselves, we'd see an end to trees.

There is a key constraining factor, though: of all the infinite variety of ways a gene could propagate itself, only a few are truly viable. One can imagine this as "islands" of reality in an infinite sea of possibility.

The islands are, from one angle, the types of life we know of. From another angle (perhaps there are lakes on these islands, with islands in the lakes, with lakes on those islands, ad nauseam) they are Kingdoms, Divisions, Phylum, Classes, etcetera.

A single gene may be able to influence the viability of its lifeform within the constraints of its island. It is exceedingly unlikely, ie. impossible, that a single gene can be responsible for shifting its next-generation lifeform from one Class to another, for instance: there's an entire ocean of "impossible non-reality" between those two islands.

But within its "island" -- which seems to me to correspond roughly to our concept of "species" -- the gene can influence the likelihood of its successful propagation.

A gene that makes an apple taste a little sweeter may make it more likely that this gene is propagated to the next generation. At the same time, making the apple taste sweeter comes at a cost: it takes energy and perhaps increases the likelihood of rot or some other form of failure.

Consequently, genes generally achieve a balance between increased propagation of the gene due to favourable effects and decreased propagation of the gene due to undesirable effects.

With the exception of radical mutation the information within genes changes very little between generations: it is an incremental process, with each combination of new genes being either very slightly "better" or "worse" at continuing the propagation of their information.

Most of the time this balance works out to be "good enough": while a radically super-sweet apple might prove to deliver the maximum probability of propagation, the small changes between generations that would lead from our current crop of apples to this super-sweet result are not so significantly "better" that natural propagation will "prefer" the "better" apple to the "worse" apple in any significant way.

There are a lot of "quote" marks in the previous paragraph, because those words tend to be loaded with meaning that is not entirely appropriate to a discussion of evolution. The words "better", "worse", and "prefer" tend to bring to mind an outside judge and controller of evolution.

Nothing could be further from the truth. Natural evolution is strictly mathematical in nature, no more judged and controlled than a weighted die that tends to roll sixes. It's a matter of statistics, of probability: that which tends to happen, tends to happen more.

The "better" genes are those that tend lead to further propagation of those genes; the "worse" genes are those that tend to reduce the likelihood of propagation, and evolution only "prefers" the "better" genes because they are statistically more likely to be propagated.

And so we conclude: the reason fruit trees make fruit is because the information encoded within the seed has, over time, had better chances of propagation when the lifeform it creates takes the form of a tree that bears fruit. At this late stage of the evolution game for trees, it appears that fruit is "good enough" for now.

A rather circular argument, I know, but that's how it works.

NB: this post is informed by the writing of Richard Dawkins. YMMV, particularly if you have been informed by competing evolutionary biologists.
posted by five fresh fish at 9:51 AM on March 25, 2004

You might enjoy Michael Pollan's excellent book The Botany of Desire, which explains how various plant species (he focuses on apples, tulips, marijuana and potatos) bend us to their will to perpetuate their species.
posted by judith at 10:06 AM on March 25, 2004

Or, rather, how the genes in those species collaborate with genes in our species to further the propagation of both species.

We like apples because they are sweet. Apples are sweet because we like them. The two are inextricably linked, insofar as humans and apples developed in parallel, one helping propagate the other by planting seedlings; and vice-versa by helping us feed our children.

I'm going to stop before I get all spooked out by the interconnectedness of all our genetic information, and whether we're anything more than some universal meme...
posted by five fresh fish at 1:31 PM on March 25, 2004

The trees don't "employ strategies" to distribute their seeds...once upon a time, a tree had a genetic mutation that caused a fruit to grow around its seeds.

The aversion to certain semantics here is amusing.

fff: Ever read Erich Jantsch? His whole career is about co-evolution.
posted by goethean at 2:00 PM on March 25, 2004

You're all wrong. Jesus put the fruit there.
posted by pissfactory at 4:14 PM on March 25, 2004

You're all wrong. Jesus put the fruit there.

Thanks for coming out but you're about twenty comments too late. I knew I should have provided crib notes.
posted by The God Complex at 4:56 PM on March 25, 2004

Also, this is ridiculously obvious, but the giant peaches and crisp apples and so on that we eat nowadays are the product of human engineering. Wild fruit is always smaller and less sweet and less plentiful.
posted by CunningLinguist at 5:37 PM on March 25, 2004

The aversion to certain semantics here is amusing.

Indeed. timeistight had a similar response to me when evolution came up January of '03. I had attributed intentionality to evolution as an attempt at useful shorthand (a technique, I'll note, also used by Dawkins.) I was told that "With something that gets misconstrued and misinterpreted as often as the theory of evolution, I think it's best to limit flights of fancy." Which just takes all the fun out of it. :-)
posted by quarantine at 7:28 PM on March 25, 2004

I'd note that most fruit that we humans actually eat has been bred over thousands of years to have much much larger fruiting bodies than naturally occur, of course, and the oddity of seedless grapes and oranges and so on is quite the slap in nature's face.
posted by stavrosthewonderchicken at 8:23 PM on March 25, 2004

Five Fresh Fish just posted possibly the best AskMe reply ever. Thank you!
posted by dash_slot- at 4:58 AM on March 26, 2004

More on seedless grapes.
posted by biffa at 5:49 AM on March 26, 2004