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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?

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?

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.

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.