I can understand why plants with seed bearing fruit might be more successful than those without, but what about plants with fruit that doesn’t contain seeds (ie the Banana)?
Why has the Banana survived with this seemingly useless feature?
A real banana has seeds. We’ve bred them out of it, because they’re unpleasant (the same reason we have seedless oranges).
These seedless plants reproduce via what amounts to cloning – cuttings are planted and grow into new plants. This has the unfortunate side effect of a strain-wide weakeness to a plague. If it can kill one plant, it can kill every one in the strain. This happened in the 60s, if I recall, and wiped out what was then the most popular type of banana.
What’s more, it’s happening again. The banana you are familiar with is a variety called the Cavendish, which replaced the prevalent variety sold a few decades ago (Gros Michel), because of its resistance to the disease wiping out the Gros Michel’s. There is now worry about a disease affecting the Cavendish:
http://www.sciencenews.org/20030308/food.asp
The little black things in the middle of the banana are vestigial seeds. Many “seedless” hybrids have underdeveloped seeds of some type, which are inoffensive enough to be eaten without noticing them.
Personally, I like the little red bananas.
Man I like the simple answers best :). I’d heard about the problem with disease susceptability, haven’t altered my banana munching habits yet though…
The bananas that are usually sold in shops are triploid: They have 3 sets of chromosomes instead of the regular 2. They have no evolutionary purpose, having been intentionally bred by humans for their bigger, almost seedless fruit. They’re sterile.
To get back to the OP, the evolutionary advantage of seedless varieties (of bananas, grapes, oranges, and even watermelons now) is that they have domesticated a species that will go to the trouble of taking cuttings, raising them with care, transplanting them and generally transporting them over the whole world.
You have to remember that selective advantage is always vis-a-vis a particular environment. And the more specialized a species is the more they will be dependent on that environment. But evolution is incapable in principle of taking a long view.
Hmmmm… a plant will develop fruit with seeds in order to “convince” animals to distribute it far and wide, and in just the same way a plant MIGHT develop seedless fruit in order to “convince” advanced primates to spread it far and wide?
They’re so smart we have wound up working for them! Was this part of God’s original design?
Well, I’ve had bosses I thought were the intellectual inferior of a banana, not to mention total lacking in appeal.
I suppose we had better watch it, though. Mr. Dilworth has warned us of the eventual outcome:
I don’t know if I’d refer to “evolution” as a description of the process, once reproduction has become controlled by an outside agency.
A plant develops fruit with seeds in order to “convince” animals to eat the fruit, thereby spreading the seeds far and wide. How, exactly, will developing no seeds serve the plant in any way, especially with respect to spreading it?
Convenience for the dominant intelligent life-form to clone them far and wide.
Certainly those seedless grapes have to be the most successful grape variety in the world.
And the master speaketh: http://www.straightdope.com/classics/a5_044.html
The triploid banana was a naturally occuring mutation that humans simply utilised. It wasn’t bred.
There’s a great park in South Florida, the Tropical Fruit and Spice Park, run by Dade County:
http://www.co.miami-dade.fl.us/parks/Parks/fruit_spice.htm
I highly recommend going there, it’s a fascinating place. Among other things, I was able to sample a wild banana. It was small and the flesh was delicious (almost had a vanilla flavor to it), but it was completely filled with round hard black seeds, the kind that would break your teeth if you accidentally bit into them. The flesh filled in the spaces between these round seeds. All you could really do was suck on the mass of seeds - it was rather like trying to eat a pomegranate.
Simple; it makes the fruit desirable to picky humans, who have the technology to widely propagate it by vegetative methods.
Not so simple: if the plant is unable to reproduce by itself, then continued generatians exist solely within the realm of (and because of) artificial selection, and the concept of “evolutionary purpose” has no meaning with respect to such a plant. It did not evolve seedlessness so that humans would select for it, humans selected them because they had no seeds. Their continued existence does not demonstrate that there is an evolutionary advantage to being seedless, but only that humans see fit to allow them to continue.
…generations…
Sure, but evolution is a blind, unplanned process anyway - the environment selects those mutations that were favourable.
If you include humanity as ‘part of the environment’, then (although we are still playing games with the concept) it becomes a little more like evolution.
There are a number of plants that have abandoned (or are in the process of abandoning) sexual reproduction quite naturally without human intervention.
It’s all a matter of viewpoint - I’ve heard it argued (although not very seriously) that cereal crops like wheat and rice are the dominant lifeforms on the planet, because of the way they have exploited so much human effort in their reproductive processes.
Actually, Garlic is a good example of a plant that has lost the ability to sexually reproduce - this is believed to be the result of centuries of cultivation by vegetative propagation.
In the wild, a mutant garlic that couldn’t produce seed would most likely eventually die out, even though it had the ability to spread vegetatively. - Humans removed this selective pressure (it may be that they even unwittingly selected the sterile mutant, if it has some incidental/related advantage such as better keeping qualities) - removal of the requirement for sexual reproduction allowed mutations that interfere with sexual reproduction to persist.
Not a lot of difference, I think between, say, removal of the requirement for sight in cave fish, allowing mutations that interfere with the visual apparatus to persist.