[slapshot]

> aren't you putting selection pressure on the diseases to be airborne?

> an airborne strain does not have an advantage over mosquitoes borne strain

There are hundreds of millions of people today who don't currently have malaria, but would be at risk to get malaria if it went airborne. Airborne malaria wouldn't be competing with mosquitoborne malaria. It'd be competing with running out of people to kill.

There seems to be a startup lesson here: your competition isn't legacy players. It's non-consumption.

[imakesnowflakes]

Sorry. I have no idea what you are talking about.

Are you a biologist/ecologist or someone knowledgeable in the field?

[jessaustin]

Instead of asking for credentials, just think a little harder. If "airborne malaria" could possibly be a thing, it would already be a thing. Plasmodium isn't a work crew responsible for killing a given number of people every year, after which they relax for a bit, only getting really creative when they fall behind their quota. It is a reproducing species that will reproduce and thrive as much as possible. There is no intelligence guiding mutation. If flying were an option, Plasmodium would be flying.

Your question is like asking, "if we rounded up all the lions in Africa and put them in pens, would they evolve wings to escape?" Yes it's that silly.

[imakesnowflakes]

Sorry. I have to ask this to you also. Are you a biologists/ecologists or some one knowledgable in the field?

[icambron]

I can tell you both the parent and grandparent posters are knowledgeable enough to help answer your question. I think you're misunderstanding how evolution and selection pressure work at a conceptual level, and you don't need an evolutionary biologist to give expert input on it any more than you need an astronomer to explain why the moon has phases.

Let me take one more crack at this: think of natural selection as evaluating `if` statements: "if this organism has the ability to spread through the air, then it is more likely to survive an reproduce". That means mutations enabling that are going to propagate. Doesn't make any mutation more or less likely; it's just a question of whether it survives and reproduces or not. Importantly, it does not say "if this is a big improvement over the status quo, keep it". The forces at play here don't know what "improvement" means and they don't know what the status quo is (though see below about competition).

The point the parent and GP were making is that the advantage in being airborne exists whether or not malaria is being killed off. Right now, before any mosquito-killing-off initiatives, a plasmodium would do very well for itself and its offspring by escaping the confines of a mosquito and infecting zillions of people through the air. Its chances of reproduction in that scenario are presumably high, because there are so many people to infect. It doesn't become more likely to make that mutation and survive the results if its vector is being killed off. It doesn't know it's being killed off.

So how does selection pressure fit in? Imagine a beetle. If you change something about its environment, say, by introducing a new predator, then traits which previously provided the beetle no advantage (say, tasting bad to that predator) suddenly provide that advantage. Then the `if` statements are decidedly different now! It's not that the tasting-bad mutation is more likely to happen, it's just more likely to impact survival. So you expect more of that mutation to survive, and soon you get a whole ton of beetles that taste terrible to our new predator. But note how this doesn't help malaria go airborne because there's no "suddenly provide an advantage" part. It was always an advantage. That it might now impact whether the species survives or isn't part of the `if` statement.

One possible way in which this can be confusing is what the GP was specifically addressing: often the value of a mutation is a function of how it affects the organism's ability to compete with the rest of the species. If there's only so much food around, then being slightly better or worse at eating it affects an organism's survival because it needs to be better at eating than its brethren or it will starve. So in that case the current state of affairs gets baked into the `if` statement. The thing to note is that this logic doesn't apply to malaria going airborne; there isn't a competition over humans to infect.

[imakesnowflakes]

Thanks for the explanation.

But you haven't said anything that I don't know already.

>The point the parent and GP were making is that the advantage in being airborne exists whether or not mosquitoes is being killed off.

When there is an abundance of mosquitoes, an airborne strain does not have a sufficient advantage over the mosquito borne strain.

Now this is an assumption I am making. And this is where you people are hung on.

You are saying that an air borne strain has an advantage even now. But what if an air borne strain is limited by distances it can travel before it dies of for want of a host? A mosquito borne strain can travel arbitrary distance and spread over a vast area..

So when there are mosquitoes, it is more or less an even match.

When you take mosquitoes out, suddenly the airborne strain gains a huge advantage over the mosquito borne strain. Right? Because there are less number of mosquitoes, the spread of mosquito borne strain is reduced. This gives the air borne strain more chance to propagate to the next generation.

If you are thinking, how does it give more probability for the air borne strain to spread? Please consider this scenario.

Let there be two indviduals A and B, A infected with an Airborne strain and B infected with a mosquito borne strain. Let there be a healthy indvidual C that is, say, 10 meters away from A and B.

Case 1: Current situtation, with an abundance of mosquitoes.

A mosquito bites B, taking in the virus and takes off. At the same time, a virus of airborne strain start from A. Now, the mosquito proceeds to bite C right away. Now the virus enters C's body. After a while, C's immune system starts a response to fight this off. A day passes. C's immune system is still fighting the infection.

It is at this time at which the air borne strain enters C's body. But there is a fight going on in there with C's immune system in full alert and is killing of off the likes of this viruses. The small amount of air borne virus that manage to enter C's body gets slaughtered before it gets a chance to grow there. C might or might not get infected with mosquito borne strain...

But The airborne strain does not propagate to the next generation.

Case 2: Mosquitoes are being killed off.

Now there is a reduced number of mosquitoes. So when the airborne strain enters C's body, the mosquito borne strain is still not there yet. Immune system has not yet started fighting viruses of this type. So it gets a head start, and ends up successfully infecting C.

The airborne strain propagate to the next generation.

[icambron]

> If you are thinking, how does it give more probability for the air borne strain to spread?

Right, that's the important thing to think about: the size of the advantage over (or even disadvantage to) the status quo doesn't matter in itself; it only matters to the degree that competition affects the viability of the new strain. I'm glad we're on the same page about that, because that's the thing I perceived that you did not understand.

On your answer to that question, if you go up to the GGP post (your first responder, Slapshot), you'll see that's exactly what they were arguing against. Most people don't have a malaria at any given time, so they're not competing for hosts. So instead of considering how our two strains battle it out in C, the dominant question -- the one that determines whether the strain is viable -- is whether it can infect A's friends D through Z, all of whom don't have malaria, presumably because they weren't bitten by an infected mosquito in the last couple weeks. Since the answer to that doesn't depend on what's happening in C, we conclude that it has about the same probability now as when mosquitos are being eliminated.

I mean, that's the whole reason we're so scared of things "going airborne", right? That they spread so much faster and frictionlessly, and they're not constrained by the vagaries of their hosts.

Not crucial to this discussion, but worth knowing: malaria isn't a virus; it's a protozoa. It does mean the immune response is pretty different.