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comicalmayhem's avatar

How have species evolved from a single cell organism?

Asked by comicalmayhem (809points) May 21st, 2011

I’m not asking you to tell me how it went from single-cellular to multi-cellular. I’m asking like how did species get all these complex organs and bodily functions? Sure, the heart pumps blood and the brain gives us intelligence and controls the rest of the body. Who comes up with this stuff?
Is it proof that God exists? Or proof that adaptation is a lot more complex than we think?

I’m agnostic and I believe in evolution, yet I’m still questioning it.

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41 Answers

everephebe's avatar

Around 3.8 billion years.

comicalmayhem's avatar

@everephebe Yes, time is a factor. But is there an argument that God could have been the deciding factor for what organs we need to perform specific bodily functions to stay alive?

jaytkay's avatar

Yes, God may have directed evolution. Or maybe not. A person who does not insist on one or the other could be described as agnostic.

everephebe's avatar

@comicalmayhem Not one that holds any water. ^^

Uberwench's avatar

If you’re not asking about how we went from single-cellular organisms to multi-cellular organisms, then the rest of the question is nonsense. The same process led to the rest, thanks to time and environmental pressures. The predecessors of organs are the organelles of the cells you don’t find mysterious. Same thing with bodily functions, which are just the descendants of cellular functions (which are bodily functions for organisms that are only one-celled).

You’ve got as much proof here of God as I have of a teapot revolving about the sun in an elliptical orbit between Earth and Mars.

mazingerz88's avatar

It does what it does. It’s up to us to observe and then hypthosize or give exact meaning to it whichever we like.

everephebe's avatar

You may also find this interesting. @comicalmayhem

incendiary_dan's avatar

It happened by random, happened to be useful, and kept going. Basically how all evolutionary change happens.

Mariah's avatar

Do you understand natural selection (not being critical, asking honestly.) The point of evolution is there doesn’t need to be a “who” coming up with it.

I’ll come back, my battery’s dying.

comicalmayhem's avatar

@Mariah Yeah, natural selection is natural. No one is behind it. Now I get that not only have species evolved, but their organs have evolved too to perform more complex tasks. Not sure if that makes sense to you or not, but it makes sense to me. Question resolved.

Qingu's avatar

@comicalmayhem, you say you’re not asking about single-cell to multicellular, but that’s a huge part of the answer. As for the “how,” we can look at some extent organisms that seem to skirt the boundary between single-cell and multicellular. For example, slime molds that act as single cells, except when conditions pressure them to act “socially” and join together into a multicellular “body.”

As for organs and organ systems, I offer the siphonophores. They are colonial cnidarians (basically jellyfish) that form colonies of individual cloned animals. What’s interesting is that certain animals in the colony specialize for certain tasks. There are polyps that specialize in digestion, medusae that specialize in “swimming” and pulling the whole thing along; in Portugeuse men-of-war there’s a polyp that acts as a “float” for the whole colony.

Siphonophores are probably my favorite animals, precisely because they so weirdly exist on this boundary between individual and group. I think if you study them and think about the implications, the idea of something evolving dedicated organs and systems won’t seem all that strange. They are also amazingly and weirdly beautiful.

To answer your question more abstractly—first of all, you have to realize that complex, multicellular creatures with organs and systems are extremely rare in the grand scheme of things. Almost every single organism that exists is a bacteria. Even cells with nuclei are comparatively rare.

Why does complex stuff exist in the first place? Because it works. Maybe another way of asking this question is “how do cooperative systems evolve”? Because multicellular and complex organisms can really be thought of as individual components somehow working together as a coherent whole. But nature is filled with such examples, and when they happen they are incredibly successful. Social insects (ants, bees, termites) are by far the most successful insect species. Cooperation is hard and rare, but evolution seems to favor it when it happens.

Qingu's avatar

Now, about “God” somehow being involved.

First of all, which god? The Mesopotamian sky god, Yahweh? The guy who couldn’t beat a tribe in warfare because they had iron chariots, and who gave humans a bunch of laws largely cribbed from the Code of Hammurabi? Or are you talking about Zeus, or Marduk, or… who, exactly?

Secondly, I’m not really sure what you’re even suggesting. You seem to accept that multicellular organisms evolved. But you think that a deity must have stepped in when it came to the emergence of organ systems?

Okay. So when did this take place, exactly? Most jellyfish don’t really have organ systems, but starfish do. So are you saying that a deity must have “taken the reigns” of evolution somewhere between basal cnidarians and echinoderms?

You can go bak int he evolutionary record—really, you can look at existing organisms—and trace a step-by-step, gradual evolution of complexity, including organ systems. Look at sponges. Then look at jellyfish. Then look at echinoderms. Then look at chordates, like us vertebrates. It’s a smooth transition from a “colony” of single cells (sponges) to a “colony” of organ systems (cnidarians and echinoderms) to a single body with complex organ systems (chordates). To suggest that a god somehow “intervened” at some arbitary stage is rather absurd.

gondwanalon's avatar

If you really want to get an idea of how species evolved from a single cell organism then read this book: “Invertebrate Zoology” (A Functional Evolutionary Approach) [Hardcover]
Edward E. Ruppert (Author), Richard S. Fox (Author), Robert D. Barnes (Author). Another good book is “Invertebrate Zoology” by Paul A. Meglitsch”. You will see how various low level invertebrate animal phyla have certain similar characteristics in internal organs and exterior form that overlaps into higher and higher animal life forms. I took two invertebrate classes as part of my Zoology major and found it interesting how much we humans have in common to earth worms and several other very low level invertebrates. By the way, did you know that E coli bacteria have the same respiration and Krebs Cycle as humans?

Ladymia69's avatar

It is what it is.

crisw's avatar


Another book you absolutely must read if you are interested in this subject is The Blind Watchmaker by Richard Dawkins. It’s written for the lay person and does a great job of explaining exactly how complexity evolved.

I think it’s also very important to point out that natural selection is absolutely not random. The most evolutionarily fit organisms survive and have more descendants. This is a constant process.

Rarebear's avatar

I’m going to countermand @crisw recommendation and instead have you read Dawkins “The Greatest Show on Earth”. It’s easier to read and written in a folksier style than The Blind Watchmaker. If you liked The Greatest Show on Earth then by all means go up a level and read TBW which can get a bit dense at times.

cbloom8's avatar

At a certain level, there is a type of living organism. In only a very small number of instances of this organism type, there can be small mutations of the organism. Some of these are negative, and some are positive, so the negatively inflicted organisms have less chance of reproducing and carrying on that trait, while the positively inflicted ones have better chances of surviving and producing. Over a very long time and over very many cases (we’re talking about millions of years and millions of cases), each little trait that allows the organism to live and reproduce better keeps passing on, and this builds up into what we are today.

Essentially, humans are the product of millions of small mutations that were beneficial to our ancestral cousins. It’s all about little changes that were of benefit, so they were passed on and continued to be present.

For example, think of human height. Smaller humans were more likely to get hurt or die than larger humans, so over time more smaller humans died and did not reproduce while more larger humans survived and did produce. The more advantageous trait was carried on and became the norm.

_zen_'s avatar

Where did that single cell come from?

How did the single cell go from that to man/woman reproduction?

crisw's avatar


You’re right; that might be a better choice. Heck, anything by Dawkins is a good choice!

crisw's avatar


You’re on the right track, but there are a couple of things I’d like to clarify.

“In only a very small number of instances of this organism type, there can be small mutations of the organism.”

Actually, we all have many mutations. For example, this study estimated each human zygote has an average of 128 mutations and this one estimated 100–200.

“Some of these are negative, and some are positive”

Actually, the most common mutations are neither- they have no effect, negative or positive, usually because they occur in non-coding regions of DNA.

“For example, think of human height. Smaller humans were more likely to get hurt or die than larger humans, so over time more smaller humans died and did not reproduce while more larger humans survived and did produce. The more advantageous trait was carried on and became the norm.”

Human height is affected by many factors (some of them non-genetic, such as nutrition) and greater height is not advantageous in every situation. Height is actually fairly variable; here’s an article on the inheritance of height.

crisw's avatar


“Where did that single cell come from?
How did the single cell go from that to man/woman reproduction?”

I am not sure how serious your questions are, as they have been asked and answered so many times.

As to where that single cell came from, first of all I want to point out that answering where life came from isn’t the purpose of the theory of evolution. Evolution just explains how life diversified once it got here.

There are many theories as to how cells formed. Here’s a somewhat technical review of the main theories- it’s older, but should give you a fair idea of some of the possibilities.

As far as “How did the single cell go from that to man/woman reproduction?”- there’s a lot more documentation for that. I am not sure exactly what you mean by “man/woman reproduction”- we humans didn’t invent sex :>)

Rarebear's avatar

@crisw but we did invent sex toys. That should count for something.

comicalmayhem's avatar

This is interesting and all, but to me, the question has been resolved.
It’s 3.8 billion years of natural selection.

Rarebear's avatar

@crisw I KNEW you’d come up with something like that!!!

comicalmayhem's avatar

@crisw I thought only humans and dolphins did sex for pleasure?

crisw's avatar


Well, first of all, in the chimp case it wasn’t for pleasure, per se; it was male chimps showing off their endowments to interested fertile females.

Secondly, your list needs to include bonobos.

Uberwench's avatar

Wait, what? All animals have sex for pleasure. It’s not like they’ve figured out where babies come from (and if they did, they might stop having sex).

_zen_'s avatar

@Uberwench I laughed hard. That was brilliant.

gondwanalon's avatar

@Uberwench There are many animal species that don’t have sex (with or without pleasure). A few include: protozoans, sponges, corals, bivalves mollusks, anemones, briozoans and barnacles. That may be the reason their evolution has been stifled. HA!

Uberwench's avatar

@gondwanalon Fair point. Change it to “all animals that have sex do it for pleasure.”

@zen Thanks!

Mariah's avatar

@Uberwench I think what @comicalmayhem and @crisw were getting at is that, if I’m not mistaken, most animals don’t feel sexual pleasure. They have sex out of instinct.

Qingu's avatar

But I bet a lot of those animals, especially ones with highly developed brains, feel pleasure at sating their instinct—just like we do.

Uberwench's avatar

@Mariah But I don’t think that is true. A lot of organisms don’t feel anything ever, but the ones that do get some pleasure out of sex (if only the satisfaction of a drive, which is the same way we get pleasure out of eating). It’s a reinforcing mechanism.

crisw's avatar


Not quite. Other mammals, at least, definitely get pleasure from sex- it’s evolution’s “reward” for procreating! It’s more that most other mammals only have sex at certain times of year, and only when the female is in season. Year-round, any-time mating is pretty rare.

Mariah's avatar

@crisw Oh okay, thanks for correcting me! I’m not sure where I had heard that other “fact,” hmmmm…

crisw's avatar


I raised goats for many years. You learn a lot watching goats :>D

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