Evolution explains development from a single-called organism to humans. How did single-celled organisms come to be. I’ve read that it might have had something to do with strands of RNA. If so how did molecules arrange in this fashion? Is this process occuring today?
The scientific theories about this are referred to as ‘abiogenesis’, or ‘how life came from non-living matter’. The talk.origins FAQ (the reference material of a Usenet newsgroup) has a section on precisely this.
Exactly on point thank you.
Evolution starts working as soon as you have things that can contribute to their own replication-- You don’t actually need cells. This is relevant for things like the self-catalyzing RNA strands.
And the life-forming process might still be happening today, but it’s hard to tell, since things that are sort of approaching alive would probably get eaten by things that are already completely alive, before they had a chance to make any real progress. In any event, all known life shows extremely strong evidence of sharing a common ancestor, which implies that the process has only been successfully completed once.
I’m puzzled to understand why this would be true. Would “nearly alive” self-replicating, er, “things” somehow have enhanced appeal for the truly alive? Wouldn’t most living organisms tend to have a genetic predisposition toward consuming food that’s reasonably common in their environment?
Classifying something as “living” is tricky. It’s all just atoms interacting at some level. That being said, evolution began at the big bang, if that’s the theory you go with.
Single celled organisms likely began as interactions between amphipathic (polar + nonpolar) molecules, which naturally conform to their lowest energy state and form liposomes, which are probably the ancestors of phospholipid bilayers as we see them today. One an intracellular environment was set apart from the extracellular environment, it’s easy to imagine how cells can develop.
That can be hard to tell, especially given some of the more extreme forms of bacteria. But the presence of DNA is a dead give away.
But I wonder: how similar would two such definitely different processes be in terms of the molecular structure? How likely it it that DNA or RNA as we know it would arise independently (probably elsewhere)?
The current theory is that pre-life earth was a “primordial soup” of organic chemicals. Frequent lightning strikes and cosmic radiation, sunlight, etc. contributed to excite atoms to combine into complex moleules. If the surface of the world, or even the ocean surfaces, teemed with such compounds (google the Miller experiments?) then the odds of self-replicating molecules of increasing complexity is not far-fetched over geological time-frames (hundreds of millions of years). Without existing life to eat it, or free oxygen to combine and wreck these molecules, they could be more and more complex - RNA, DNA helix, Virus-type constucts, and then attracting coatings of other complex molecules to protect them from the elements, until we have life. Evolution on the molecular scale.
Another theory says hundreds of millions of years, or billions, is not too short for a giant meteor to knock debris off one planet that could contain life land in ideal conditions on another… considering scientists claim to have found quite a few martian projectiles in the antarctic. So maybe there was just one bio-creation…?
No, that’s not the current “theory”. It’s one of several current hypothesis, and one that has the most current support.
I want to point out that evolution is a Scientific theory, in other words a FACT. There is solid testable proof of Evolution.
Abiogenesis is a scientific Hypothesis , in other words a educated guess. It has not been proven. It looks good, but it’s just a interesting idea, and it could be wrong. Life on Earth could have originated via Panspermia, for example.
Abiogenesis is as close to a proven fact as it’s possible to get. What’s in question is the mechanism of abiogenesis. But there is definitely life now, and there definitely was a time when there was no life, and the transition from one to the other was, by definition, abiogenesis.
Knorf, there’s no real way of knowing how likely it is for DNA and RNA to arise. But even if those molecules did happen to arise independently multiple times, that’s not the end of the comparison: You’ve also got the genetic code, which determines how a particular sequence of DNA translates into a particular sequence of amino acids. Every known lifeform uses the exact same genetic code, and the chances of that happening by chance, even if you’re starting with DNA in all cases, is combinatorically slim.
Never had a dog, I take it? My dog ate all kinds of things not around as dogs evolved. If the new molecule shares characteristics with things cells eat, it will get eaten, or it might get eaten accidentally, since would be no reason for a cell or other life form to evolve away from eating it.
Darwin called it descent with modification. If your self-replicating molecule does not replicate perfectly, and if there is some reproductive advantage in certain structures (such as faster replication or more stability, but not too much) you will have evolution. There might be self-replicating molecules much simpler than RNA which evolved into RNA.
Generally, abiogenesis is how life on Earth started. A solid scientific minority thinks Panspermia is the answer, not abiogenesis.
wiki:
*Abiogenesis (pronounced /ˌeɪbaɪ.ɵˈdʒɛnɨsɪs/ ay-by-oh-jen-ə-siss) or biopoesis is the study of how biological life arises from inorganic matter through natural processes, and the method by which life on Earth arose. *
Yes, but Panspermia is just a different flavor of Abiogenesis. It’s just a question of where the Abiogenesis took place.
Having said that, Abiogenesis can’t really be called a theory, since it doesn’t tell us how it happened. By comparison, evolution wasn’t really a new idea in 1859, but Evolution by Natural Selection was the theory (I guess it was still a hypothesis when Darwin first proposed it).
What categories of food do dogs today eat that dogs 10,000 years ago didn’t?
My dogs have resolutely stayed away from available sources of food like leaves, grass and (mercifully) garden veggies. So “near life” that was closer to plant than animal would probably have been quite safe from them.
Panspermia doesn’t answer the question, just pushes it out into space and further back in time.
The “nearly alive” primordial soup probably consisted of small organic molecules which are the building blocks of biochemistry. I.e. amino acids, sugars, lipids, and a smattering of more complicated structures. And that stuff is great food for bacteria, since they can simply absorb it and use it directly. Or, if it can’t be used directly, bacteria are astonishingly good at extracting energy and resources from just about any organic molecule.
In fact, any hypothetical “primordial soup” would make an excellent bacteria growth media.
True, which is why John Mace does make a good point. Life had to begin somewhere and other than a Divine Miracle, abiogenesis has to be the answer. However, Life on Earth may not have occured that way. There is no scientific evidence for abiogenesis, it’s just a rather good hypothesis.
College level Biology 2xx.
It’s is certain that this process is occurring today. The universe is so vast that any possible combination of chemical elements and physical conditions that sparked life on Earth is absolutely certain to be happening in vastly many other places right now.
Voyager was referring to things dogs eat, not to food. As any dog owner can tell you, there’s a big difference between those two categories.
DrDeth, creation of life by divine miracle would still be a form of abiogenesis, unless you consider the deity to be “alive”. Admittedly, that would be a form of abiogenesis which would be particularly non-amenable to scientific study.
As for panspermia, I’ve always thought the notion absurd. Of all places in the Universe we know of, the one most hospitable to life is right here. To posit panspermia is to posit that life developed even quicker than we currently think, in an environment far less hospitable. Or possibly it traveled all the way from another hospitable environment, but that adds such a huge travel time that it just makes the problem of it being quicker far, far worse. In any case, there would still have had to have been an abiogenesis event somewhere.