Is there an evolutionary drive towards more complex organisms?

February 19, 2005 9:14 AM

Is there an evolutionary drive towards more complex organisms? Douglas Rushkoff believes there is: ”It appears obvious, yet absolutely unconfirmable, that matter is groping towards complexity.” [link] I've taken it for granted, but is it really true? What do we know about this?
posted by Termite to Science & Nature (25 answers total)

According to Stephen Jay Gould in his book Full House, there is an illusion of a drive to complexity because life initially evolved in its minimally complex form. Since life does have a tendency toward diversity, it manifests itself in an increase in complexity.

To further explain, it's likely impossible for a bacterium or virus to evolve into a simpler form of life as the new variation would be unable to fulfil the requirements of life. However, as the diversity of life increases (as it does tend to do), it is relatively simple for a more complex form of life to arise. And example of this is the prokaryote/eukaryote changeover.
posted by stet at 9:29 AM on February 19, 2005

Evolution is non-teleological, which is to say it is not goal oriented. Complexity is not the end of evolution- for example, we could say that horses are more highly evolved than humans because they have many more bones than we do, making them more complex creatures. But of course this is asinine because one cannot say that one organism is more highly evolved than any other- such comparisons are ultimately useless in describing the way a species evolves.
posted by baphomet at 9:33 AM on February 19, 2005 [1 favorite]

This is a tricky question to answer, mostly because you would have to specift what kind of complexity you had in mind. Natural selection (and other forms of evolution) don't really have any long term goals. In fact, the evolutionary reaper's blade acts incredibly locally.

In cases where the local predators are many, the organisms around would have to evolve very complex defensive and offensive capabilities to stick around. Where there are fewer predators, the offensive and defensive capabilities would be set adrift, but the better organisms might evolve very complex ways of digesting food or attracting mates efficiently.

That seems to suggest complexity is inevitable. But in many cases a so-called "simpler" solution might be beneficial. Presumably this is why, over time, some birds lose their wings and ability to fly. The energy expenditure to keep up the wings just isn't worth the benefit. The point here is more that complexity is in the eye of the beholder. In some ways, sloths are just as complex as human beings.

What does seem to me to be the holy grail of evolutionary design is something low-cost that can adapt to many different environmental conditions at a rapid (i.e. non-genetic) pace. So if organisms with these qualities evolve, and such a thing is complex, then evolution will favor complexity. Of course, birth rates would have to be checked somehow so that it didn't just eat up all the resources. Presumably this is what we have in humans with the capability for learning as advanced as it is. But we only have a nice prototype of the type of super-adaptibility I'm suggesting.
posted by ontic at 9:40 AM on February 19, 2005

>one cannot say that one organism is more highly evolved than any other- such comparisons are ultimately useless in describing the way a species evolves

Mmmm. I'm not sure if it's completely useless. One could map successive rounds of replication error or the bifurcations in a phylogenetic tree to give some indication of complexity -- the why and how. It's a huge grey area so I'll defer to better arguments.

On the drive towards complexity. I do think the idea that evolution is non-teleological is right. Plus, complexity as a concept is like intelligence, it does not hold up well to reification.

So, to completely piss over my last statement, in answer to your question. I would say complexity is like order. And entropy is an important force in the universe. Therefore, if there is a drive towards complexity there has to be an entropic cost, as referred to by Erwin Schrödinger in "What is Life?"

From that, organisms could be goal orientated and complexity their fate --therein lies religion.
posted by gsb at 9:49 AM on February 19, 2005

I have a piggyback that might help narrow down the discussion a bit: in this months "Scientific American," there's an article about the recently discovered "hobbits" in Indonesia. The article contains all sorts of views about them, including many skeptical views. At one point, the article discussed the fact that these creatures had tiny brains. It then says, "... why would selection downsize intelligence?"

I started thinking about that and wondering about it? Would natural selection ever favor lower intelligence in a species that had already developed higher intelligence. Obviously, the answer is yes, if lower intelligence became an adaptive advantage. But would it ever become one? In what circumstances?

I know that reasons for the evolution of high intelligence are controversial. It seems somewhat reasonable that it evolved to help manage complex bodies, use of tools, and social interaction. What reasonable scenarios would take these uses away?
posted by grumblebee at 9:50 AM on February 19, 2005

Different organisms have used different tactics to stay competitive. Humans have gotten insanely complex. Developed all sorts of neurons to do all sorts of things.

Bacteria on the other hand, survive because they're so simple. They have safety in numbers. You kill one group off, and you speed up evolution, selecting for a resistant group. The fastest growing bacteria, if they had unlimited resources, would divide to become the size of the earth in 24 hours, starting from just one.
posted by gramcracker at 10:14 AM on February 19, 2005

grumblebee: I think the way to answer the question 'in what circumstances would lower intelligence become an adaptive advantage' is by turning it around and saying 'in which situation is higher intelligence no longer an advantage?'. Intelligence appears to require a big brain and all the problems that come with it - increased metabolic load, requirement to keep it safe, long development period, etc etc. I can imagine that in some specialised situations, the extra energy spent on having a big brain might not be as well spent as having lots of kids instead.
posted by adrianhon at 10:19 AM on February 19, 2005

Lots of interesting stuff and links in the Wikipedia article Self-organization. (I started by searching for Ilya Prigogine.)
posted by gimonca at 10:21 AM on February 19, 2005

To understand the extreme view of Gould's hypothesis, read up on the random walk. Essentially, divergence can be broad without being goal oriented.

Another example is diffusion, like the process that allows you to smell something across the street. The particles that enter your nose didnt arrive because their "goal" was to spread outwards and conquer the space. Rather, they are just acting randomly and yet still expanding into the space around them.
posted by vacapinta at 10:26 AM on February 19, 2005

> Evolution is non-teleological, which is to say it is not goal oriented.

But there are (confusingly to many) two perfectly valid styles of explanation: deterministic, focusing on initial conditions to explain a given outcome, and teleonomic, focusing on the end state as a way to organize the consideration of the events that led to it.

> one cannot say that one organism is more highly evolved than any
> other- such comparisons are ultimately useless in describing the
> way a species evolves.

"More highly evolved," no, "Better adapted," yes. We are of course each of us exactly as far evolved from the primordial living thingie as each other of us is, because that's measured in clock ticks. But there is an independent criterion for evolutionary success beyond merely survival and reproduction, namely efficiency. Well-adapted organisms survive and reproduce because they exploit their environment more efficiently, wasting less of the available energy to inefficient processing and system friction than competing organisms do. This criterion is what saves Darwinian evolution from circularity (Q: What is evolution? A:The origin of species. Q:Why is there evolution? A:Because species originate.) because it reduces not to biology but straight to thermodynamics.

> According to Stephen Jay Gould in his book Full House, there is an illusion
> of a drive to complexity because life initially evolved in its minimally complex form.

It is the nature of evolution that it has tended, as a general rule, toward increasing complexity over time, because 1. it started at the pretty-much-irreducibly-simple end, not very efficient but then competition was nil; 2. the appearance of competition generates pressure toward increasing efficiency, which means being increasingly fine-tuned to take better advantage of available energy resources. In practice, fine-tuning is most likely to be achieved by increased complexity, and that has been the case over the course of natural history. As to whether this evident tendency/directionality constitutes an illusion or not, refer to deterministic vs. teleonomic explanations, super.
posted by jfuller at 10:26 AM on February 19, 2005

Baphomet: Evolution is non-teleological, which is to say it is not goal oriented. Complexity is not the end of evolution- for example, we could say that horses are more highly evolved than humans because they have many more bones than we do, making them more complex creatures. But of course this is asinine because one cannot say that one organism is more highly evolved than any other- such comparisons are ultimately useless in describing the way a species evolves.

Pedantryfilter: while I agree completely that evolution is is commonly seen as teleological when it is most certainly not, I must note that the average adult horse has 205 bones while the average adult human has 206.

Grumblebee: I am not sure anyone is proposing that the "Hobbits" were less intelligent. Brainsize commonly scales with body size, and, apart from that, in modern humans there is little to no correlation between brain size and intelligence. It is primariliy about the complexity of the brain architecture and it is possible to imagine the same island-endemism driven selective pressures that produced small body size amongst "hobbits" (fuck I hate that stupid nickname) also producing highly efficient small brains.
posted by Rumple at 10:42 AM on February 19, 2005

Response by poster: Just a quick clarification while reading your answers. A human, a lizard and a shark are perhaps all on the same level of complexity. When I said "more complex organisms" I was thinking about single celled life compared to larger organisms, plants compared to animals, insects compared to mammals...
posted by Termite at 10:45 AM on February 19, 2005

To me it seems as simple as, life becomes more complex as it adds new feature to make it more competitive. It's like saying "are computer OSes intrinsically destined to complexity by a law of nature;" no, it's just that their development is skewed toward what makes them popular, which is usually more features.

(I realize that an intelligently designed piece of software is not at all akin to evolution, but it's just a metaphor)
posted by abcde at 11:04 AM on February 19, 2005

Response by poster: And the obvious follow-up questions: did the evolution towards more complex organisms stop when larger animals entered the stage (fish, reptiles, mammals)? Or are more complex organisms evolving today (if so, where)?
posted by Termite at 11:08 AM on February 19, 2005

We're currently the most complex existing animal, by most standards. That could make humans the strongest candidate for being the next stage in evolution, but the consensus is we're probably not evolving any further due to prolonging the lives of the weaker members, etc.

Incidentally, insects sprung from the ocean in a separate incident than mammals, who as you know came from fish. You probably knew that, but you made it sound like it was a linear progression.
posted by abcde at 11:31 AM on February 19, 2005

It's worth noting that while some lineages have become more complex over time, many others (e.g. bacteria, blue-green algae, viruses) have merely become more diverse over time while remaining simple. "Simple" doesn't necessarily equal "evolutionary loser."
posted by jfuller at 11:54 AM on February 19, 2005

One might observe that simple organisms must arise before complex organisms, first by probablity (chance of self-replicating RNA strand that takes radiation and builds nucleotides arising is greater than chance of multicellular elephant suddenly arising fully-formed from primodial soup) and second by practicality (simple things can sit around and live on photons: more complex things have to wait until these simple things develop so they can eat them.)

I think we'll find that as the sun burns out the tendency is towards more simple organisms (last inhabitant of the earth is a microbe catching the last few photons). We're existing in a happy anti-entropy pocket driven by enormous increases in entropy in the sun, but that is only short-term (e.g. last and next few billion years).
posted by alasdair at 12:24 PM on February 19, 2005

this is a really cool blog about biology, and some of the posts talked about this (well, they talked about is there an evolutionary drive twoards bigness). Might want to take a look.
posted by delmoi at 12:58 PM on February 19, 2005

This is not a scientific question; it is a metaphysical one. Is the universe absolutely random? (...and what does that mean, exactly? Random seem to imply that it is not governed by laws.) If so, then I guess it must be an accident that I have higher (or "higher", if you prefer) thinking abilities than my cat, for example.

The scientific consensus has an answer: Rushkoff is wrong. There is no evolutionary drive towards complexity. But this answer follows from the metaphysical assumptions of scientists; not from observation or experimentation.

There are a few evolutionary writers (Prigogine, Jantsch, Robert Wright) who have given up these assumptions and found that things make more sense without them. But they are studiously ignored by the scientific mainstream.
posted by goethean at 3:08 PM on February 19, 2005

There are so many definitional lacunae in the original question (well-intentioned though it was) that it is meaningless.

First of all, most of the respondents are going on the assumption that, in fact, complex creatures like humans, sharks and whatnot are evolutionarily successful. I would point out that prokaryotes have been around for billions of years and in one day I can generate more of them in an Erlenmeyer flask than there have ever been humans to walk the Earth. From this perspective, the absurdity of an idea like "evolutionary drive towards" or "evolutionary success" may become more apparent. It doesn't mean anything unless you define it. If you look at the diversity of Prokaryota as compared to, say, the primates, again they have us well and truly licked.

Of interest, over the last 5 years of the Human Genome project, the estimate of total genes in the human genome, which is a possible metric of complexity, descended from 100,000 to 50,000 to where it is now, "25,000-30,000". However, bear in mind that Morgan and his Drosophila buddies looked at chromosomal number as a metric of complexity. They found 4 chromosome pairs in the fruit fly, and 23 in humans, which was all well and good until someone discovered a salamander with 250 or thereabouts.

Indeed, we may not know enough to posit a useful definition of complexity; an above poster referenced 'social interaction', and a brief foray into, say, Konrad Lorenz reveals the extraordinary intricacies of our fellow-traveler species, as yet poorly understood. I suspect that most of the "complexities" of life, however defined, are still obscure to biologists.

Finally, I like Neal Stephenson's summary of evolution, badly paraphrased: "We're all badass motherfuckers, because we are the descendants of badass motherfuckers who survived. Everything now alive is descended from badass motherfuckers who survived." In this view, complexity is merely an epiphenomenon.
posted by ikkyu2 at 3:43 PM on February 19, 2005

As a really basic take on the question (which I believe many are complexifying in completely unrelated directions), one way to interpret evolution theory is that evolution is feature-oriented. Organisms that have better features than others for a given environment have a competitive advantage and survive. Because the ecosphere is of limited size and volatile, over time a competitive pressure develops for organisms to provide better sets of features, which leads to greater complexity in order to provide these features in the most flexible manner - simply because an organism can't implement more features without greater complexity.
posted by azazello at 4:45 PM on February 19, 2005

billions of years and in one day I can generate more of them in an Erlenmeyer flask than there have ever been humans to walk the Earth. From this perspective, the absurdity of an idea like "evolutionary drive towards" or "evolutionary success" may become more apparent.

This is sort of the point I was trying to make with evolution as diffusion. We only need "features" because we are forced to inhabit the farthest reaches of the adaptive landscape. It doesnt make us better, it just makes us equipped for the environment we are forced to inhabit.

An analogy: The Prokaryotes are like a civilization that has occupied a rich tropical region. We have been forced to move out and become Himalayan mountain dwellers. Just because we have fancy things like Oxygen Tents and Climbing Gear doesnt necessarily make us more fortunate.
posted by vacapinta at 4:56 PM on February 19, 2005

Response by poster: Thanks for your answers, and a special thank you to Delmoi for The Loom. I've just read "Eyes, part two". Excellent.

Some of you seem to think I said "better" (and proceed to explain that single celled organisms are just as evolutionary successful as humans), but I didn't. I said "more complex", as in large organisms compared to single celled life, animals compared to plants. And let's not get lost in definitions. Complexity might be a... well, a complex concept, but it shouldn't be hard to see that a gazelle is a more complicated organism than an amoeba.
posted by Termite at 11:16 PM on February 19, 2005

As a biologist who studies evolution I was pleased at how spot-on so many of these answers were. Few people fell into the pitfalls of teleology or anthropocentrism.

Termite, sure, I will give you that. In almost every metric you could think of, a gazelle is more complex than an amoeba. But as baphomet asked, is a horse or a human more complex? Why? There are too many different ways to answer that question that I don't think it can be done definitively.
posted by grouse at 4:30 AM on February 20, 2005

what baphomet said. ecologists only recently have begun making the point that there isn't one straightforward way to talk about complexity, because different animals have different strengths and weaknesses to suit their particular needs. i think the major example my prof cited most was molluscs; they seem incredibly simple physiologically, but some have some really freaky mental wiring that allows them to do certain tasks far better than say, birds or other more "complex" animals.
posted by ifjuly at 8:43 AM on February 20, 2005