I don’t think oranges always have a multiple of five segments - the flower has fivefold symmetry, for sure - but the inside of the fruit is a little bit more chaotic (the rind has fivefold symmetry though - you can sometimes see this best in the little creases around the stalk and calyx, and in the pattern made by the oil glands in the skin.
[QUOTE=IOMDave]
unnatural selection? 
What the HECK is that thing?! :eek:
Bananazilla is coming to get you…
[/QUOTE]
ETA: deleted obvious statement.
[QUOTE=Peter Morris]
designed?
… by some sort of intelligence? :dubious:
[/QUOTE]
Well, yes. A human one, or one, as **brazil84 **said. **Colibri **himself acknowledged that oranges in nature aren’t so strongly segmented. It’s not a leap to guess that humans designed oranges, through breeding and hybridization, to have segments which tear apart easily, as well as to be large, juicy and sweet.
Just like basset hounds were literally designed, by human breeders, to have short stubby legs so that hunters on foot could keep up with them at a trot. (Or so I’ve heard.)
In the natural world, “designed” is indeed a land mine of a metaphor. But once you’re talking a domesticated breed of plant or animal, it’s entirely appropriate.
[QUOTE=IOMDave]
unnatural selection?
[/QUOTE]
Called “artificial selection” in my old textbooks. AKA breeding.
[QUOTE=Colophon]
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…
[/QUOTE]
Just grabbed one off a colleague and counted. 11.
[QUOTE=Colibri]
Why on Earth would you think that’s what I meant?
[/QUOTE]
Relax, dude, I was just teasing you. Get a sense of humour, m’kay?
I’m sure you don’t *really *think that oranges were “designed.”
[QUOTE=Surok]
Just grabbed one off a colleague and counted. 11.
[/QUOTE]
Ah yes, but was one of those an undersized “adventitious segment”, as it were? I notice you often get one segment smaller than the others.
Hmm… Johnny Citrus & the Adventitious Segments - I’d pay to see them in concert.
[QUOTE=Surok]
Just grabbed one off a colleague
[/QUOTE]
You have an orange tree for a colleague?
[QUOTE=Peter Morris]
Dividing the orange into handy little segments makes it easier for monkeys to eat, and thus better for spreading the seed.
[/QUOTE]
Are we certain this has nothing to do with it? I would have thought that a segmented fruit that breaks into handy bite sized pieces has a survival advantage over a less-segmented one.
If humans have selectively bred oranges with that feature, then isn’t that a survival advantage anyway?
I’m not a biologist, but many other fruits apart from citrus are built up of mutiple similar parts, e.g., raspberries and pomegranates, to take two wildly different shapes. Might not the reason be that it’s easier to build up a larger fruit by having multiples of the same structure rather than by having a larger single structure? And an evolutionary advantage to have a larger structure to make it easier for the animals to find the fruit, eat it, and disperse the seeds.
[QUOTE=Peter Morris]
designed?
… by some sort of intelligence? :dubious:
[/QUOTE]
Design does not imply intelligence any more than selection does. (For some reason people generally try to avoid the former while accepting the latter as ways to characterize evolution, but I’ve never been quite sure why.)
-FrL-
[QUOTE=Colophon]
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…
[/QUOTE]
In the interest of science, I just forced myself to eat an orange. 10 segments, all full sized.
doesn’t it? Looking at the dictionary, it gives lots of definitions for design, most of them directly state some sort of intelligence
http://dictionary.reference.com/search?q=design
definitions include:
[ul]
[li]To plan and fashion artistically or skillfully.[/li]
[li]To form or conceive in the mind; [/li]
[li]To plan out in systematic, usually graphic form:[/li]
[li]To create or execute in an artistic or highly skilled manner.[/li][/ul]
and so on
On a related note, appropo the oranges structure relating to the flower-- Did you know that each length of corn silk in an ear of corn represents a single kernel of corn on that cob?
That, is the number of kernels on a cob equals the number of lengths of corn silk.
Okay, in the interest of science (and teaching counting), my daughter and I just peeled an orange and counted segments.
After removing the lubricious integument* from a Sunkist navel orange, we found nine (9) large, equally sized segments, one (1) small, half sized segment, and a hard navel with an indeterminate number of its own compartments.
*Og as my witness, I never dreamed I’d be able to work it into conversation this soon! 
[QUOTE=Colophon]
Ah yes, but was one of those an undersized “adventitious segment”, as it were? I notice you often get one segment smaller than the others.
[/QUOTE]
No, they were all full-sized.
<OT>
And Cervaise, I will suggest to my colleague that an orange tree costume would be appropriate garb for the upcoming Christmas party.
</OT>
[QUOTE=Peter Morris]
If humans have selectively bred oranges with that feature, then isn’t that a survival advantage anyway?
[/QUOTE]
Not really. We breed them to eat, not to make seed-scattering more efficient (indeed, when was the last time you planted the seeds from an orange - or any other fruit - that you ate?). If anything, it’s a survival disadvantage (in the long term), as the juicier and more managable the fruit slices from a particular tree, the more likely that tree’s fruit is to be sold at market and consumed, and its seeds subsequently discarded. At least, until the seeds are bred out of the fruit entirely, at which point the plant’s survival becomes entirely dependent on humans.
Artificial selection has little to do with advantages to the organism, and everything to do with how that organism can be modified for our needs/wants.
[QUOTE=Darwin’s Finch]
Not really. We breed them to eat, not to make seed-scattering more efficient
[/quote]
Yeah, but orange farmers plant seeds from trees that produce the best oranges, and discard seeds from the less good ones, don’t they? A plant that produces the best oranges, (best from the human POV), gets its genes passed down to the next generation.
Isn’t that what evolution is all about?
Funnily enough, about 3 months ago I had an avocado for lunch and on impulse decided to plant the stone in a pot. Now I’ve got a little plant growing on my window sill. Maybe in about 5 years I’ll have my own crop of avocados.
[QUOTE=Peter Morris]
Yeah, but orange farmers plant seeds from trees that produce the best oranges, and discard seeds from the less good ones, don’t they? A plant that produces the best oranges, (best from the human POV), gets its genes passed down to the next generation.
[/QUOTE]
Nah, it’s all hybrids and splicing onto rootstocks these days, innit? I’m sure the oranges we’re eating are all clones of the same two orange trees somewhere in South America. If you plant the seeds, you’ll get wildly different trees from them.
Fascinating; there doesn’t really seem to be a definitive answer yet. From biological geometry, to selection.
I think Giles idea makes a lot of sense. The mechanical principles behind building something big out of smaller substructures are well known (Eiffel Tower anyone?). If this is simply an efficient design principle then that could be all there is to it. Not so much a case of why, as why not.
Perhaps the precurser to the modern raspberry was a “single segment” raspberry that then underwent a mutation (twins!). As this would be perfectly sustainable, there would be no real disadvantage to it; the advantage would be that animals would be more likely to eat from that particular plant because there was more of the good stuff. Natural selection at work.
Perhaps something similar happened with the orange. Perhaps I’m talking out of my ass.