Evolution: When did it start? How?

Great Debates
1

I thought these might be GQ, but seeing as how they relate to the Evolution vs Creationism debate…

I first posted this in another thread. Seing as it was a semi-hijack, and anyway got completely ignored, I figured it was better off in its own thread.

First:

In response to the “how could man have evolved from apes?” question, several posts in Creationism vs. Evolution threads state that the first Homo Sapiens Sapiens showed up about 120,000 years ago. But how can we say that? Wouldn’t it be more accurate to say that the earliest fossil evidence we have of a creature that seems to match Homo Sapiens Sapiens dates to around 120,000 years ago? That’s certainly much less definitive. Given gaps in the fossil record, we’re still fudging. Plus, we’re going on skeleton shapes. Without DNA evidence to match, couldn’t we still be off by a good margin? Or do we have other evidence to support this time frame?

Second (and this is the one that I’m really vague on):

So, life somehow evolved out of non-life, but where do we draw the line between the two? What do we consider to be the first/most basic form of life? Wouldn’t this organism need to have reproductive capabilities at the start, so that the simplest form of reproduction did not evolve later, but was initially present? Otherwise the “first life” would die and we’d be back at square one… What constituted this first reproductive mechanism?

2

I’ll just take a couple of stabs, here:

Yes, certainly it’s true that this is more accurate. Here’s a cultural difference between the scientific community and the mainstream. When a scientist says “the first Homo Sapiens Sapiens showed up about 120,000 years ago.” they mean “the earliest fossil evidence we have of a creature that seems to match Homo Sapiens Sapiens dates to around 120,000 years ago.” Part of scientific literacy is having a vague idea how scientific inferences are made, and knowning, at least broadly, which statements are pretty bomb-proof, and which don’t really have that much evidence to back them up. I agree to some degree that scientists should be more careful about making such statements for a public audience, and I also think that the media do a rotten job of conveying what is certain, and what needs a lot more research before it’s accepted. But it would also take up a lot of space to properly hedge every scientific statment. The best solution, I think, is education–trying to acheive a moderate level of scientific literacy amongst the public.

As an aside, it’s not just fossils, but cultural remanants that such a statement is based on, like tools, for example.

On the first life, that’s certainly still an open question. The first lifeform does not still exist today. It would have been very primitive, and would have been wiped out by the subsequent species that could out-compete it. The oldest lifeforms today are extremophiles that like really hot environments, like ocean vents–but whether life originated there, or whether, at some point, all life except for extremophiles was wiped out, we can’t say.

The question of what the first life was like was discussed this morning (Friday, August 4) on Earth & Sky, a radio program. Here’s the link to today’s show, but it will expire tomorrow, so you’ll have
to “Browse” for it:

Briefly, there’s a controversy between whether it was a large reproducing molecule (a primitive form of DNA/RNA) or whether the frist lifeforms were bubbles of lipids that surrounded beneficial chemicals (those that kept the bubble together) and kept out harmful ones.

As I recall from high school biology, the characteristics of life are that it 1) grows, 2) reproduces itself (which viruses cannot), 3) consumes resources, 4) excretes waste, 5) responds to its environment.

3

Absolutely, if you require precision in your statements. However, I think that the vast majority of readers, at least on this board, are sophisticated enough to grasp the idea that “the first H. s. sapiens” means the first evidence for H.s.s., not “that which we can categorically state was the first-ever true man to exist.” That kind of authoritative statement should be made about a date in late October 4004 B.C. in the Iraqi province of Eden, if it’s made at all.

Second on that subject, when you’re talking fossil subspecies, the distinction rests more on the opinion of the discoverer than on any objective distinction – this is true even for species, as comparison of Ian Tattersall’s work with the Leakeys and Johansen’s writings will show. Tattersall is a “splitter” and has about three times as many fossil hominid species as either of the other systems do.

Well, almost every bit of paleontology is based on fossils, most notably bones in vertebrates and shells in mollusks, so you’d be throwing out nearly everything we know about life before about 10,000 years ago. The fight about whether Neanderthals were Homo sapiens or another species is still going strong; “archaic Homo” is a handy term that means whatever you want it to in terms of post Homo habilis anthropology. There are some cultural characteristics that distinguish early H.s.s. from H.s.n., or H.s. from H.n. if you prefer. I’ll have to have notice on any details on these; it’s my wife who’s the paleoanthropologist, and I’m quite hazy on precisely what demarcates the line between them.

Sex was a later development. Bacteria developed it, but did not use it in anything like plants, animals, and protists do. Here are two “traditional” demarcations:

  1. The first nucleoprotein – DNA wrapped in a protective protein coating that it coded to produce – was the first life. It flourished in a “soup” of organic molecules that it could match up pieces of itself from, and reproduced in this way.

  2. The first cell was produced by a DNA molecule being absorbed into a “coacervate” – a globule of fat and protein that it took over and managed by its chemical coding. This constitutes the first “life-as-we-know-it” with the DNA floating around in the soup being considered pre-life. It reproduced by its DNA coming to code for not only itself but the surrounding protoplasm in the former coacervate, which became its cell body.

More recent theories suggest that life originated around ocean-bottom vents, and of course Svante Arrhenius has the hoary old theory that life developed elsewhere than on Earth and floated through space in some sort of spore structure, colonizing early Earth once it got here.

The reason you’re vague about the origin of life is because everybody else is, too.

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4

I don’t see any inconsistencies brought up by your first point. Sure, you could say, “the earliest fossil evidence we have of a creature that seems to match Homo Sapiens Sapiens dates to around 120,000 years ago.” What’s the problem? As for DNA evidence you don’t necessarily need it. It is remarkable what forensic scientists can tell from bones. The give size, sex, nutrional information, locomotive abilities (upright, on all fours or a combo of the two) and perhaps a rough estimation of intelligence based on skull size.

In the end they can point to what they have of the fossil record and say this fossil is more like than unlike modern humans while that somewhat older fossil is closer to an ape or monkey. It can be a bit vague but it sets a reasonable starting point give or take a few 10,000 years.
As to your second point that can be dicey. It turns out a rock solid definition of life is difficult. Life eats, breathes and reproduces? Well, so does fire but we don’t view fire as ‘alive’ in the usual sense.

That aside the precursors to life were amino acids…the basic building blocks of life. Some scientist somewhere built a sealed chamber where he threw in the basic junk found in very early earth’s atmosphere and then ran electricity through it all to simulate lightning. Sure enough, after awhile, amino acids were formed from the soup of early earth’s atmosphere.

As to reproduction early life would have done it via cell division. The very first life was almost certainly a single cell organism. Current reproduction still shows this although it’s a bit more complex than way back when. A single cell with 50% of the genetic code meets another single cell with the other 50% of the code. Cell 2 drops the code off then the single cell starts dividing and reproducing till a human (or a cat for that matter) is formed. The real difference now is cell specialization and the sheer number of cells that group together to form an organism.

5

[…shivering…]

Oooo, I know you didn’t intend it that way, but that statement, on its face, is a bit spooky. There is a fine line between education and indoctrination. Just please be meticulously ethical if you decide to educate us.

6

Ahhh…clear, detailed responses. Thanks.

I often hear the creationist argument that it is impossible that both life and the ability to reproduce would come into existence simultaneously in the same organism. It’s made me wonder about the mechanics.

It sounds like what we’re saying here is that primitive replication mechanisms existed in organic chemical compounds prior to the point where something existed that we would call life. So in some sense the state of “being alive” is something that evolved, and the evolutionary process was already in full swing prior to the existence of life.

From my perspective, this has profound implications in understanding the questions that evolutionary theory seeks to answer, and in clarifying the creationism vs. evolution debate. It implies that evolutionary theory is not really concerned with the origins of life.

For instance, in the thread about kansas vs. evolution, Maeglin said:

This statement makes a lot more sense to me now.

7

Ren said:

In response to the “how could man have evolved from apes?” question, several posts in Creationism vs. Evolution threads state that the first Homo Sapiens Sapiens showed up about 120,000 years ago. But how can we say that? Wouldn’t it be more accurate to say that the earliest fossil evidence we have of a creature that seems to match Homo Sapiens Sapiens dates to around 120,000 years ago?

Yes, what you’re saying is more accurate, but I think something needs to be pointed out. If you took the 120K bones and compared them to a recently deceased human, you’d find no significant differences between the two. That’s also assuming they’re of the same approximate age and sex.

Also note, I said “significant” differences. The human body varies, but we’ve been able to map out those variations and account for them. The bones that are 120K years old would fall well within the variations that modern humans show.

Therefore, I think it’s safe to say that the 120K old bones ARE of Homo sapiens.

8

Is it the word “scientific” that makes you shiver, Lib? If you remove that word or replace it with, say, “mathematics” or “musical”, do you still go into fight-or-flight reponse?

9

For an interesting look at a new theory about how life started, try At Home in the Universe by Stuart Kauffman.

10

I don’t have time to fully explain, but I’d suggest that anybody interested in the evolutionary branch that led to humans should check out the new book, Extinct Humans, by Ian Tattersall and Jeffrey Schwartz.

It’s a bit steep at $50 (though cheaper when you take off whatever discounts you can get at various sellers), but if you really are interested, I think it’s worth it. Among other things, it has a ton of photos of the various fossils to help explain what they’re talking about.

I talked to Schwartz for about an hour and a half the other night – I was interviewing him for an article I’m writing about it – and the length of the call alone should tell you how interesting I found the whole discussion. I was talking to him about stuff I had no intention of writing about (too complex for a general newspaper audience). Again, I would encourage anybody with an interest in this subject to get the book.

11

Spiritus

Um, no, I have not stopped beating my wife, and neither have I stopped not beating her, since I have not ever beaten her.

The word that made me shiver was the word that I remarked upon: education. I said there was a fine line between education and indoctrination.

I am not afraid of science. I am afraid of politics.

12

So, if someone said, “the best solution for an illiterate population is teaching them to read” you would shudder?

I was not accusing you of beating your wife. I was asking you to explain your reaction. I cannot help it if that makes you defensive.

13

Spiritus Mundi:

Lib was making a reference to a rather infamous “entrapment” question. Namely, how would you respond if someone asked you “Have you stopped beating your wife?”.

He was basically saying that when you asked:

… you were giving him the same type of loaded question, because either a “yes” or a “no” answer implies that he goes into a fight-or-flight response when he hears the word “scientific.”

14

And speaking of the first living organisms, one of the candidates for the first protocells are proteinoid microspheres, discovered by Stanley Fox (of Fox-Miller Experiment fame) when he soaked hot proteinoids in a mild salt solution. They have many properties in common with full-blown cells, including the ability to grow and divide, but they do not contain any genetic material.

Here are some pictures: http://www.siu.edu/~protocell/photos.htm

15

Tracer:

I am familiar with the reference. However, my original question did not imply he went into a fight-or-flight response when he heard the word “scientific”. In fact, I was quite specifically asking him whether it was that word or something else which inspired his response. He “shiverred” and called the sentence “spooky”. I was asking what part of the sentence caused this reaction. He answered that it was the word “education”.

I admit, I find that attitude unusual on a board dedicated to fighting ignorance. shrug

Unless you quible with the characterization fight-or-flight for a response of shivering and feeling spooked, I don’t see how you can imply that I attributed a behavior to him that he had not claimed for himself.

16

Spiritus

Well, let me spell it out as plainly as I can: I have no problem with education, but I do have a problem with indoctrination. The line between them, I believe, is thin enough to merit vigilance.

17

Well, to answer some fine points in the OP:

Life is not well defined. Even today there is some argument about whether viruses and other similar organisms are truly alive. A virus is really just a hunk of nucleic acid with a protein capsule, yet it’s capable of reproducing itself. So what is it?

As fo rthe origins, one of the prevailing theories is that RNA is the precursor to life. RNA has been shown to be able to autocatalyze its replication. This solves a few of the problems inyherent–like which came first, RNA or proteins? Until it was shown that RNA can catalyze its own replication, you have a problem–you need RNA to make proteins (since DNA is still a long way off), but you need proteins to make RNA. Now, however, RNA thrown together by chance could replicate itself. So this is a pretty decent guess at origins–though still just one theory…

18

Podkayne wrote:

The code for the life itself, versus the protective shell that houses it. Now if that doesn’t sound like “Which came first, the chicken or the egg?”, I don’t know what does!
As an aside, even the people in the “bubbles came first” camp have trouble choosing which kind of bubble came first. The three major candidates are:
[ul]
[li]Lipospheres,[/li][li]Proteinoid microspheres, and[/li][li]Coacervates[/li][/ul]
Lipospheres are the least likely candidate, because they do not grow or divide. Both proteinoid microspheres and coacervates have been observed growing and dividing.

19

Of course, ther’s also the possibility that both are correct–many of the organelles seen within cells apear to have been independatn organisms/thingies at one point, that were simply integrated in because it was beneficial to both…

20

There is a really interesting new argument for the “first life” thing. Imagine that life didn’t start as genes, but rather the padding in between the genes.

Most “higher organisms” have a genetic structure in which the gene is coded on exons, interrupted by introns. The neat thing is when you make RNA, some introns excise (splice) themselves out of the transcript. One of the ideas for the first life is the ribozyme – a ribonucleic acid with enzymatic properties.

Imagine primitve life as a bunch of ribozymes. They could reproduce themselves and do some enzymatic reactions to facilitate growing. There are RNA molecules which can do this even today. It became favorable for them to eventually make a “hard copy” in DNA, since RNA is much more labile than DNA. If you can reproduce an RNA molecule, reproducing a DNA one is not such a stretch. Later, it became advantageous for them to concatenate their hard copies, which they assembled by self excision to form new ribozymes when transcribed. Things first start to resemble intron/exon structure. Later, protein translation evolved (still helped a lot by ribozymes), and the cell started to move from an ribozyme dependency to an enzyme dependency. As enzymes took over for ribozyme function, some ribozymes became less crucial, and were selected against. Some may still have retained their excision abilities, leading to the intron/exon structure seen today.

So, you ask, why do “primitive” organisms like bacteria not have any introns (their genes are transcribed in one run without a need for splicing). Easy. Bacteria are just MORE evolved than us eukaryotes. They have moved further away from the ribozyme arena and closer to a complete enzyme/gene dependency.

To me, this is allows for a smoother transition between early life just springing forth to the functional microorganism. I like it much better than the microsphere/micelle type approach because it has something which can actively be selected for at all stages of the game.