I was eating an orange tonight and it occoured to me that I have no idea why they should come in handy, easy to eat segments. Is there some sensible reason for this (from an evolutionary standpoint)? I could understand if it wasn’t surrounded by a fairly thick, tough, layer holding the whole thing together.
IOMWife thinks it has something to do with each segment providing nutrients for the pips, in much the same way as nut flesh provides fuel for the little bit that actually grows when all is said and done. The oranges we were eating were some kind of funky hybrid that don’t have a pip issue, so based on current evidence it seems reasonable, but not definitive.
I never thought about this before, but it’s an interesting question. Here’s a logical guess.
The biological purpose of fruit is to spread the seed. The tree provides a source of nutrition to animals, and they drop the seed away from the parent tree.
Dividing the orange into handy little segments makes it easier for monkeys to eat, and thus better for spreading the seed.
Don’t think so. Fruit is for the animals that eat it, not the seed itself.
That seems to make a certain amount of sense, but wouldn’t a monkey (for example…I don’t know what usually eats oranges) just devour the thing without bothering to split it up, or for that matter peel it?
I don’t think there is any particular adaptive reason for it. The division of a citrus fruit into segments is simply a consequence of the structure of the original ovary. Similar structures are found in many other fruits. And you should remember that a cultivated orange is very different from a wild fruit. The original form did not divide into segments nearly so easily. It is very unlikely that the segmentation is designed to make it easier for fruit-eating animals to eat; most such animals do not peel the fruit and divide it into segments.
Ok, since we seem to be drawing a collective blank on this one, here goes my most educated WAG. The structure of the fruit comes from the structure of the flower that gave place to it. Most dycotyledon plants (my guess from spanish, sorry if it is not the exact word) have their structure in fives or multiples of five (monocotyledon plants go in threes or multiples).
All fruits have this same radial symmetry in numbers according to their types. Cut an apple through its equator and see how the seeds are arranged, and see the star shaped figure in the middle. Go crazy with whatever fruits you can find.
That the segments are fully separated in the case of citrus is probably the product of the ovaries of the flower being separated. I do not think citrus is a bunch of separate fruits. Citrus flowers are solitary and I believe the fruit comes from a single ovary.
Many other fruits show separated segments (carpels?). Tomatoes for example, and peppers. Just to give you an idea of different fruit arrangements.
As for this being an advantage, it doesn’t have to be. Plant evolution improvises a lot.
It is not necessary for every feature of an organism to confer some evolutionary advantage for that feature to exist. It is only necessary that it not confer an evolutionary disadvantage.
I would WAG that the segmentation of citrus fruts falls into this category. It exists as a result of the structure of the flower. It persists because it doesn’t impede the plant’s reproductive processes.
Because you unconsciously used a metaphor which included the appearance of intentionality, even though it means no more than that anyone actually designed an orange to be conveniently segmented than that a photon ‘decides’ to go through one slot or another. (Or that it is someone’s conscious awareness of the cat that causes it to be alive or dead.) British moral “philosopher” (and I use that term loosely, even within the normal ambiguities one makes for philosophy) Mary Midgley gets much mileage out of the unfortunately use of the term “selfish” in regard to the game theory of genetic competition and Richard Dawkins’ hypothesis of extended phenotypes even though he and others make it aptly clear that no intentionality or volition exists on the part of a gene. In the case of speaking of the design of naturally evolved organisms, it should be understood that the design is the result of optimization for survival and reproduction between competing groups of organisms, not teleological organization.
As for why oranges are segmented, Colibri and Sapo have it right. The orange, and indeed all citrus fruits, are evolved from flowering forms, and the segmentation is an extension of the locules of the ovary. The same is true, I think, in fact for any fruit which contains multiple seeds. Although it is not obvious from the structure of the modern varieties of apples (which are highly artificially evolved for human consumption), the fruit of all members of genus Malus is at least rudimentarially segmented into five sections, as careful dissection of the fruit will show. One might as well argue a bee’s understanding of analytical geometry and mechanical design from the hexagonal structure of the hive as to reason from the supposed perfection of fruits.
And in regard to Kirk Cameron, a friend of mine recently passed around the link to the video to her coworkers to add some levity to the day. Apparently one coworker watched the video with the sound off while doing other work, and then wondered how Cameron had gotten into fruit fetish porn. “…the Tom Cruise of nutty fundamental creationist Christianity,” indeed.
Especially considering that the banana as we know it is a cultivar, quite different from its wild ancestor. In particular, wild bananas have huge, inconvenient seeds in them, and are only marginally useful as a food item:
If you think of man as a fruit eating animal, and that mankind has cultivated oranges that are easier to eat, then couldn’t one say that this is a kind of evolution and that indeed oranges are divided into segments because they are easier for people to eat that way?
How easily-segmented are the wild varieties of citrus, or the nearest wild relatives? I don’t know, but if I was to make a prediction, I would say “not very”, and the modern fruit are as removed from their antecedents as maize is from teosinte. They have easily-seperated segments because they were intelligently designed - by us!
Of course, if varieties like the Buddha’s Hand citron turn out to be wild, this theory will need revising.
Hmm, I just grabbed an orange (well, it was a clementine actually) and it had, yep, 10 segments. I’ve never counted before - is this usually the case? It was the last orange in the bag so I can’t check another one at present…
