[aroch]

Sterile hybrids are not a new thing nor are they something that only occurs with human intervention. Darwin's finches routinely mated in pairs that produced sterile hybrids. Vegetative reproduction (ie budding or from cuttings) is also quite common in plants -- there are several plants that vegetatively reproduce by only their leaves. Human aided vegetative propagation is no different from herbivore aided propagation caused by a herbivore burying part of a vegetatively reproducing plant

[anthonyb]

The several varieties of bananas that you'll see in the store are most definitely caused by human intervention (actively trying to cross slightly different plants to produce a new hybrid) and propagation. Normally hybrids die out in the wild.

Also, once you have a sterile hybrid, there's not much in the way of selection pressure. And since bananas are clones, there's nothing for the selection pressure to act on.

[codeflo]

Not quite true, if I understand you correctly. Clones are a form of asexual reproduction, not that different in principle from what is observed in bacteria. So plant clones do undergo mutation and natural selection.

[anthonyb]

I don't know about bacteria, but a banana variety is all essentially the same plant, propagated from a central stock. Have a look at the controls around planting and growing your own bananas, it's all red tape, permits and extremely fascist:

http://www.backyardbananas.com.au/faq.html

http://www.daff.qld.gov.au/plants/fruit-and-vegetables/fruit...

And for very good reason: every banana of a variety is susceptible to (eg.) a virus outbreak - there won't be any pockets of genetic variability like you would get with potatoes or citrus. If anything that affects bananas becomes widespread - no more bananas.

[codeflo]

I was replying specifically to "since bananas are clones, there's nothing for the selection pressure to act on." That's not correct reasoning, since the DNA in plant clones can mutate, and thus, plant clones are susceptible to selection pressure.

[anthonyb]

In theory, yes - but mutation rates of clones are going to be very, very low. Bananas are also grown from a central stock to control disease, so even if there were a mutation, all the bananas are going to mutate identically.

Bacteria reproduce in all sorts of bizarre ways, including swapping DNA from other bacteria, editing their DNA, etc., so it's not really related.

[codeflo]

I think we can all agree that what's happening with bananas is not a healthy state of affairs. I was just trying to clarify that asexual reproduction doesn't exclude natural selection, and was using bacteria as an (admittedly not perfect) analogy.

I guess if you had simply said that there's virtually no selection pressure, you wouldn't have triggered my nitpick reaction. :)