Evolution ("by non-random natural selection")

I... what... I don't... -brain leaks out ears-

Too bad we're probably not going to be evolving on a wide scale unless we lose all our technology. At this point humans have probably conquered natural selection.

edited 9th Oct '12 5:57:31 PM by Kostya

Not really. It kind of depends on what you call "natural selection". People are still selective about their mates, for instance.

True but I mean in the sense that all the weak humans die off so traits that are disadvantageous are removed. This probably won't happen as much. Just as an example my girlfriend has a frail immune system and can't process gluten products. Years back she probably would have died early on from these problems but now we have medicines and special diets that can accommodate her needs. So if we ever got married and had children they could inherit these traits whereas before they would be phased out.

edited 9th Oct '12 6:05:19 PM by Kostya

You would be willing to marry a girl who could be killed a a loaf of bread? You're sweet

Ok, how about the origin of life? Any opinions?

If I remember correctly, they've managed to create amino acids by running electricity through a projected "early earth atmosphere" simulation.

Edit: Here, if you're interested. One of many.

edited 9th Oct '12 6:22:41 PM by DrunkGirlfriend

It's not that severe. She apparently had it her whole life but it was only diagnosed three years ago and she ate gluten things up until it was discovered. It partly explains why she's been sick most of her life but I think it would have killed her already if she was going to die from it. My main point was that with both of these things weakening her severely she probably would have died if we didn't have all the modern amenities we have now.

Thank you though.

I don't know what to think about that. As far as I can tell no mechanism has been decided upon although scientists have apparently caused amino acids to spontaneously synthesis by mimicking the early conditions of Earth's oceans.

edit: Ninja'd.

edited 10th Oct '12 1:15:17 PM by Kostya

Well, the main problem, so far as I can tell, is that DNA and RNA are such complex molecules that no one thinks that they spontaneously developed as the first step in organic chemistry. But what came before? That experiment that drunk Girlfriend linked to, the Miller-Urey, basically demonstrated that energy + certain common elements including carbon, = a very basic organic molecule called an "amino acid". Life (to simplify a lot) basically consists of complex chains of such amino acids called "proteins". DNA is a protein. All known forms of life use DNA or RNA molecules as templates to guide the formation of the complex proteins that life uses. The challenge is to come up with a plausible model describing how, under natural conditions, simple amino acids floating around in ancient seas combined themselves into complex chains with no DNA or RNA guiding the process. So far, no one has solved this. In fact, the basic set-up utilized by the Miller-Urey experiment cant be it- the apparatus they used bears no resemblance to the physical conditions on the primitive earth.

It's a real mystery, particularly since there is no known chemical pathway by which simple organic molecules could self-assemble into RNA. According to the other wiki (scroll down to "Molecular Biologists Dream") "...the problem of emergence of self-replicating RNA molecules as any movement towards an RNA world on a properly modeled early Earth would have been continuously suppressed by destructive reactions."

This has been used as an attack on evolution by fundamentalists. From the page I linked to:

"However, also on the basis of the evidence that not even one of these above ten steps has been shown to occur fully naturalistically in a plausible early Earth scenario (e.g. without the input of human intelligent design) and in fact for steps 1-3 alone "there was not enough time, and there was not enough world" that "the right combinations of circumstances would happen," I therefore conclude that the origin of life via this RNA world was at least what Christian philosopher/ theologian Norman L. Geisler calls a "second class miracle," i.e. a "supernaturally guided event ... whose natural process can be described scientifically (and perhaps even reduplicated by humanly controlled natural means)"

So- without doubt an important problem.

Important, yes, but not insurmountable. Absence of evidence does not equal evidence of absence. Science has solved trickier conundrums and there's no inherent reason to believe it can't solve this one. "God of the gaps" falls victim to the inevitable closing of the gaps.

Fair enough, but I was hoping for a little free-wheeling speculation on what the process will ultimately turn out to have been.

Do I look like an organic chemist? My lay knowledge is sufficient to understand the question, but not to guess at the answer.

Edit: The "not enough time and not enough world" bit is argument from incredulity, as there was more than enough planet and more than enough time for nucleic acid chemistry to develop. The Earth is a pretty big place, and a billion years is a lot of time. And we haven't ruled out the idea of the impact of a cometary body carrying organic molecules, either, although I have to say that if you're relying on "space rocks" to make your theory of life work, you're reaching a bit.

edited 10th Oct '12 12:04:39 PM by Fighteer

Honestly if we're going with a non-divine explanation then I think it was just random chance. The molecules linked together in such a way that they gained the ability to respond to their surroundings. Now obviously this is a gigantic freak event but given a long enough timescale and the right conditions it's not surprising that it happened. Once they linked together and formed the first...I guess it would be a cell at this point. Anyway once they made that all it has to do is reproduce and life would spread out from that.

The obvious question would be "Where did the organic material on the rock come from?"

edited 10th Oct '12 1:21:03 PM by Kostya

"Organic" just means that it contains carbon, you know.

Chances are, organic compounds were able to form randomly in early-earth conditions. No space rocks required. Granted, the most commonly accepted theory is that comets brought water to the early earth though.

edited 10th Oct '12 1:23:32 PM by DrunkGirlfriend

Cells as distinct entities didn't form for quite a while. Lipid membranes maintaining a stable internal environment were indeed a huge evolutionary step up, but they weren't the first step by a long shot.

Edit: I think that, in the long run, the explanation for why DNA/RNA as they exist today became the dominant (indeed, the only) form of life on the planet is the same as for just about anything else in evolution: because countless trillions of combinations were attempted, and this is the one that succeeded.

edited 10th Oct '12 1:39:30 PM by Fighteer

Oh yeah. I often forget that.

Do lipid membranes do that nowadays? That would be a pretty big hint about whether or not that's how things started.

Cell membranes are far more complicated affairs now than at their origin, but at a very basic level, yes, they're composed of lipids. The ability to maintain a stable internal environment was critical for the development of complex structures. Previously, you were just a bunch of RNA molecules floating around in a liquid soup and vulnerable to any old random chemical reaction that you bumped into.

Right, it's exactly like floating in a bubble.

edited 10th Oct '12 1:52:44 PM by Fighteer

Er, yes? Plant cells (usually) have a rigid cell wall, but the rest of them have a bilayer lipid membrane.

It's entirely possible that it formed without intervention too, since it's simply a double layer of molecules that are partially hydrophobic, which makes them form "bubbles".

It's horribly simplified, but that's the general gist of it.

edited 10th Oct '12 1:52:07 PM by DrunkGirlfriend

In fact, viruses are the evolutionary descendants of pre-cell-membrane organisms, if I remember correctly.

Edit: Not entirely. Most viruses have a protein shell and some do in fact have a lipid membrane.

edited 10th Oct '12 1:56:38 PM by Fighteer

I could see that. They're really only snippets of RNA encased in a protein shell.

Edit: In general though. Whether or not they have a membrane doesn't really affect the way they function, but could be another byproduct of evolution, where it helps protect them against defenses.

edited 10th Oct '12 2:01:05 PM by DrunkGirlfriend

The article on viruses' lipid membranes says that they are generally pilfered from the host cell and have molecules designed to allow them to enter other cells more readily. In short, the virus doesn't construct its own cell membrane, but "borrows" it for protection and disguise. Tricky things, those viruses.

But all viruses have a DNA/RNA core and a protein shell that protects them and contains their primary mechanisms for invasion. Lacking an integral membrane puts them on an evolutionary pathway divergent from cellular organisms.

edited 10th Oct '12 2:05:38 PM by Fighteer

Sort of. There's potential for a lot of overlap, like the theory that the internal structure of a cell developed in a symbiotic way, where various virus-like bits were "captured" by the membrane at an early evolutionary stage, and later became the organelles.

This is particularly compelling when you look at mitochondria (or chloroplasts in plants), since they're self-replicating independent of the rest of the organelles.

edited 10th Oct '12 2:11:03 PM by DrunkGirlfriend

Yeah, it's a crazy incestuous world at the micro-organic level. In fact, don't mitochondria have an entirely different reproductive mechanism?

Edit: Hmm, no, they have their own DNA.

So mitochondrial DNA represents a divergent evolutionary path, after the basic building blocks of DNA had already evolved, but while there was still competition for how cell structures would be formed.

"Its", not "It's". "Its" is the possessive; "It's" is the contraction of "it is".

edited 10th Oct '12 2:17:34 PM by Fighteer

Yeah, it also contains its own DNA, and said DNA is very similar to some bacterial genomes.

Edit: Yeah. That's what lead to the "cells are composed of symbiotic organelles that were absorbed at an early evolutionary stage" theory.

Editedit: It contains it is own DNA. Happy?

It's cold in here, can't type right. Bleh.

edited 10th Oct '12 2:18:51 PM by DrunkGirlfriend

"Led" is the past tense of "lead".

edited 10th Oct '12 2:19:20 PM by Fighteer