Question about complexity...

[cj0]

Hello, just been doing some research and trying to find some answers.

 

I've been reading that more complex life tend to be found in the higher layers of the fossil record and more simplistic life tend to be in lower layers. However, I've been trying to find what makes one form of life more complex than another. Is it chromosome count? Being a multicellular organism? Asexual vs sexual reproduction? Consciousness and higher brain functions?

 

I don't think a high number of chromosomes alone makes one form complex since some single celled organisms have exponentially more chromosomes than humans. Still, it seems odd that while humans possess a type of consciousness this one protozoan (Oxytricha trifallax) has so much more code in its DNA. Also, I am not sure if consciousness qualifies one organism to be more complex than another.

 

I just want a good answer on what is the criteria used to determine which species are more complex than others because I haven't found one yet.

 

 

[iNow]

The term generally refers to structure, function, and physiological processes.

 

There's a whole field of biology for it and this link gives an overview: http://en.wikipedia.org/wiki/Complex_systems_biology

 

And a great article from PNAS on the subject is available here: http://www.pnas.org/content/106/16/6433.full

[Endy0816]

Yeah, I would say traits are the defining feature.

 

Code length also plays a role in helping to correct and limit the damage caused by mutations, so there won't necessarily be a correlation to complexity.

[StringJunky]

On the subject of relative gene numbers: : Why Onions Have More DNA Than You Do

[cj0]

It seems like from some of the articles that the definition of a complex system is not completely agreed upon. Regardless, you could say a bacterium is less complex than a mammal considering a mammal has more interacting parts within its own system.

 

Also, I know that on the lowest levels of the fossil record there are more plants and sea creatures (like sponges). So there are levels in which ONLY relatively simple life is found. Then, you start to find fish intermixed with them, and then amphibians, reptiles, birds, mammals right? So eventually more types of species are found together (simple and complex living and dying together).

 

My question is, are most of these animals necessarily more complex than others (like ancient mammals and reptiles vs modern mammals and reptiles) or are they just different expressions of genetic material? It would seem to me that a dinosaur isn't necessarily less complex than a modern crocodile even though they are so much older. Likewise, are ancient plants actually less complex than modern plants?

 

Furthermore, how do we compare ancient species with modern species with regards to complexity if we don't necessarily know what their internal systems were (although the bones do tell us a fair amount about their lifestyle)?

 

Please correct me if I am wrong on anything I've written above as well, I'm kind of new to this.

[Greg H.]

Here's another article (from the NY Times) on junk DNA from this year.

[StringJunky]

Organisms don't necessarily tend towards complexity unless selection pressures bias them that way. I don't know if this will clarify but the 'goal' of an organism, and hence evolution, is to make copies of itself, not to increase in complexity. If an adaptation increases an organisms' chances of reproducing it will be passed on. Likewise, if the loss of a trait improves its chances of reproducing it will be passed on; It can go either way and still be successful.

Edited April 22, 2015 by StringJunky

[CharonY]

The term generally refers to structure, function, and physiological processes.

 

There's a whole field of biology for it and this link gives an overview: http://en.wikipedia.org/wiki/Complex_systems_biology

 

And a great article from PNAS on the subject is available here: http://www.pnas.org/content/106/16/6433.full

 

I am not sure whether systems biology applies here. Systems biology is mostly concerned with (emergent) properties of complex biological networks, but these can be fairly simple in absolute terms. For example, any cell is more complex than we (or any branch of systems biology) can exhaustively handle. But in the context of OP it would be a simple system.

 

If we dive into the molecular level it becomes entirely arbitrary. Eukaryotic cells have more complex morphologies (due to more prominent compartmentalization). Yet most bacteria have more metabolic variability.

 

I would posit that in the given context the most likely parameter is morphological complexity, including the development of specialized organs.

Edited April 22, 2015 by CharonY

[cj0]

So if someone says evolution predicts that we should find less complex organisms evolving into more complex organisms in the fossil record they not exactly right. Yes, it would have to start small (and the beginning would probably be chemicals coming together and creating self replicating molecules) until we get to uni cellular organisms and multi cellular organisms, etc. But evolutionary theory really doesn't have anything more to say than that when it comes to complexity.

 

But there does come a point in which (for the most part) the life around today is not really more complex than most of the life found in the fossil record and there isn't really a definite gradient of upward complexity seen throughout the fossil record. Just that at one point only this type of life existed, then more complex life began to be found with the simple life, then even more complex life is found with that life...etc.

 

An exaggerated example being: just plants and sponges on lower levels; then plants, sponges, and fish; then plants, sponges, fish and amphibians...and so on. But reptiles and mammals today are not necessarily more complex than reptiles and mammals millions of years ago (unless you count consciousness as making one form of life more complex than another).

 

Is this pretty accurate or not so much?

 

Also, are mammals considered the most complex and if so why? Is having more interacting organs and interconnected systems within an organism make it more complex than another?

[CharonY]

 

 

Is this pretty accurate or not so much?

 

Also, are mammals considered the most complex and if so why? Is having more interacting organs and interconnected systems within an organism make it more complex than another?

 

I would agree in general with that statement. The thing is that if enough time passes there is a chance that a new mechanism comes into existence that may allow new levels of complexity. Such as the development of an active cardiovascular system that overcomes the limit of diffusion and allows for larger, more complex body sizes and structures. But as we have established, there is not a single value or aspect that we could use to gauge overall complexity; after all all extant organisms, from bacteria to whales share the same historic time frame. Evolution is more about horizontal, rather than vertical hierarchy, so to speak.

[cj0]

 

I would agree in general with that statement. The thing is that if enough time passes there is a chance that a new mechanism comes into existence that may allow new levels of complexity. Such as the development of an active cardiovascular system that overcomes the limit of diffusion and allows for larger, more complex body sizes and structures. But as we have established, there is not a single value or aspect that we could use to gauge overall complexity; after all all extant organisms, from bacteria to whales share the same historic time frame. Evolution is more about horizontal, rather than vertical hierarchy, so to speak.

Wow, that actually helps explain a lot. Ever since I was a kid I've been taught that life was always moving from simple to complex across time, but the more I've read the more this hasn't made sense to me. Thanks for all the answers, its been very helpful.

 

One more question though, is this misunderstanding (especially in popular science media) a big problem in your opinion? Also, what other common misconceptions (besides "Why are there still monkeys?" because that is easy to answer) should I be on the lookout in my reading?

Edited April 23, 2015 by cj0

[StringJunky]

>>

One more question though, is this misunderstanding (especially in popular science media) a big problem in your opinion? Also, what other common misconceptions (besides "Why are there still monkeys?" because that is easy to answer) should I be on the lookout in my reading?

To pinch from Dawkins, always remember, Evolution is a blind watchmaker.

[Endy0816]

it is indeed:

 

[Jennycooper]

Genetic complexity is beyond our imagination and there are a lot of cases on earth showing genetic mutation powerful effect. Complexity found everywhere in human, animals and other organisms.

[overtone]

 

 

It would seem to me that a dinosaur isn't necessarily less complex than a modern crocodile even though they are so much older. Likewise, are ancient plants actually less complex than modern plants?

Crocs are older than dinosaurs, and both of them have been evolving right along (dinos into birds).

 

If one is looking for complexity from evolution, the location of it would be as much within the larger populations of beings as in any single organism. Plants, for example, over evolutionary time have greatly increased in complexity as a group - the older plant designs are still represented (snake grass, ferns), new ones came along and added new forms (woody plants, pines and the like), and then yet more innovations in basic design (flowering plants, especially) - so that after some hundreds of millions of years we have what any reasonable measure would call greater complexity: all the old plant designs still around, plus the new ones. This is so regardless of any increase in the complexity of individual plants.