The Cambrian Explosion has been debated/researched for a long time, its about 530 million years ago with the explosion of life in the seas, we get a lot of complex multicellular organisms here as well.
i guess, the main thing people look at is ‘why’ well, I didn’t really know either but after thinking about it for awhile it seems kinda obvious, though i’m probably only painting a tiny picture of the reality of why the explosion happened.
First we get the first true eyes, not just jellyfish being able to go up/down based on light sensitive cells, but actually complex eyes, we see this with the pile of fossilized arthropod eyes, made out of that hard-crystal like mineral, perhaps more importantly we see the first evolution of both jaw and gut somewhere in the cambrian explosion, and maybe even skin.
My point is that as complexity rose and eyes/jaws/guts came into play, it created a true diversity explosion through an arms race, and we see the result of that arms race in a lot of the fossil animals from that period.
Any one want to add potential explanations for the cambrian? mine may be weak.
The evolvability of arthropods and etc might just exceed that of the Ediacarans before as well. That segmented body-plan, opens a lot of options for expanding/diversifying into different niches as well.
god-damn arthropods!!!
it could also have been just a type of getting to a certain level of genetic complexity, in which, mutations arise more commonly and in different ways, or some such as well.
I believe that oxygen levels played an important role as well. Fermentation is terribly inefficient and photosynthesis isn’t an option of a lot of creatures. Around the Cambrian, oxygen levels in the atmosphere got high enough to start supporting some of the more complex heterotrophs. Basically, increased oxygen levels made a whole lot of niches available when they previously weren’t. And, well, nature abhors a vacuum.
I think Xunz has the correct emphasis. The Cambrian was simply a “window” of extreme opportunity for life experimentation, the result of favorable environmental conditions and almost a totally unexplored panopoly of unfilled niches. Interestingly, just a little less than 10% of the life forms we have found in the Cambrian are the lines of every living animal today. It’s almost comforting to know that life is capable of throwing away 90% of it’s experiments. I’m betting on the cockroach…
But probably only after rising oxygen levels corresponded with some of the earliest Ediacaran biota remains, which gave other organisms some reason to develope some ability to consume them like Kimberella allegedly.
I must have misread that. It seems like you are suggesting that decay would have given rise to oxygen. So would you please rephrase that so I can understand it correctly?
That was worded poorly. What i mean to say is that rising oxygen levels correspond with the arrival of some complex multicellular life during that early time frame before the cambrian.
As in, only after these organisms existed would it have been beneficial for other organisms to evolve parts to say, eat them, or whatever. I mention one such life-form from the period, that perhaps fed on early life of that time-frame.
OK, that makes sense. I’m glad I did misunderstand that. But still, for what you are saying to be true, it would require more advanced auxotrophs to have come first. I mean, by the Cambrian, ferns had already overtaken the land. When I think of the Cambrian explosion, I generally think of heterotrophs. I mean, ferns had already taken over the land by that time. Just a matter of O2 building up. After all, oxygen is horrifically poisonous shit. That really changes the game.
Well I assume complex auxotrophs came first seems a reasonable assumption to make before heterotrophs, but the heterotrophs probably would have existed before locomotive heterotrophs in almost auxotrophic(sp) form, not the relevant definition of them though. Like some of the biota of the period before the cambrian looked highly highly plant like in all ways, except it existed in places where allegedly it couldn’t get any sunlight, so they assume it somehow absorbed shit from its environment.
less complex cellular life I would assume, of some sort. I meant that, even after plant-life it would have been even more beneficial to evolve ‘eating parts’ with these animal-like-plants being around. Sitting there unable to move.
(
Though, keep in mind my knowledge about the Cambrian and period before that are fairly sketchy, and elucidation that anyone can give me on the area, any interesting facts or book suggestions, always appreciated. Not so much the life-forms as some environmental variables, probably)
Like, the common ancestor between the heterotrophs and auxotrophs? We share different genes in signaling pathways with some plants, don’t we? Well, there’d have to be a common ancestor even if we didn’t, even if it was long dead. right?
Oh dear, I was out of it the other night. I apologize. I meant “autotroph” when I wrote “auxotroph”. Does that make more sense? I can see how that would have been confusing.
I’m not an evolutionary biologist, but its the only carreer I could ever imagine for myself and is my only passion. I’ll either be an evolutionary biologist one day, or a bum on the street with a sign saying “FUCK: I wish I was an evolutionary biologist”.
shit, I also mixed those terms up when you originally used it. every time i’ve used “Auxo” I meant; creature which gains its ‘energy’ from photosynthesis or whatever and not from organic molecules or organic life.
I have a few books on the Cambrian and the period before that as well, many of the books are full of speculation and so forth, and with biology advancing at this great rate I figured there’d be better materials out now. (well, scientific speculation).
though, why do I never check wiki’s ‘further reading’ list, I don’t know.
My god, why did I not know about this interactive tree of life? I mean, i have a few books with trees, but thats pretty intense.
Another note on biology, I think I heard venter tell Dawkins that molecular comparison of the biology between species to determine ‘relatedness’ makes no sense due to contamination of the genome with massive amounts of virus or bacteria or whatever.
I have no idea what he could possibly mean by that. I’ve seen him support molecular taxonomy by saying that he personally looked at the genome and seen evidence that we’re descended from a common ancestor and share genes across the animal kingdom to determine say that we do indeed share a common ancestor with chimpanzee.
Does he mean only that saying that a sponge shares say 70% of our genes is a meaningless statement because its the combination of genes that count? (70% of the same genes switched on and off in different ways creates well, obvious and massive differences) or that we can’t determine how related we are in comaprison to a monkey and a cat.
Because the second, which it almost seemed he was suggesting just doesn’t make much sense to me; at all. Not only me, but Richard Dawkins while admitting that he could certainly be wrong about that and all other scientists that support it, didn’t seem to know wtf Craig Venter was talking about.
What he’s saying is that because of viral transfer of genes that the common view of a common ancestor (when we find really similiar genetic markers in species) gets throw n out the window.
Alright this is Venter’s call: Because of transfer of gene or gene sequences from species by bacteria/viruses, the common view of common ancestors could very well be wrong or at least largely inaccurate.
IF a molecular taxonomist takes some bone and one from another species and does dna testing and finds stretches of say very similiar dna, the anwser today is; common ancestor.
But he’s saying that we’ll have to overhaul a huge amount of molecular taxonomy, because the consideration of gene transfer in other ways across species isn’t taken into consideration.
Which sucks because molecular taxonomy provided a pretty clean cut picture. I guess thats the way with science, if Venter turns out to be correct; it can be messy.
Though the way in which molecular taxonomy is done by statistical methods would seem to almost make this criticism already dead, if that was the case, wouldn’t it just be small amounts of ‘noise’ to be filtered out? But again, venter mentions that up to 1/3 of genomes can be viral contamination.
The future of molecular taxonomy might be; Sifting through viral data to make molecular taxonomy decisions based on the genome thats left, but than, we don’t understand as much as we think we do, if that needs* to be done.
Richard Dawkins replied on the forums to speak about this video.
"Towards the end of this conversation, beginning around 42 minutes and 17 seconds, Craig Venter and I had an argument. He said that cross-contamination of eucaryotic genomes, via viruses, is common. I was extremely sceptical, and I pressed him several times, to see if I had misunderstood him. It is an extremely important question because, as I pointed out in the discussion, if cross-contamination is common it makes molecular taxonomy difficult or impossible. I don’t think I did misunderstand him, and I am now more than ever convinced that he was wrong. Today I consulted my colleague Jonathan Hodgkin, Oxford’s Professor of Genetics, who confirmed my scepticism. Professor Hodgkin knows of only three somewhat equivocal examples: in nematode worms, in Drosophila and in bdelloid rotifers. The bdelloids seem to be the only major group where cross-contamination is widespread. This could be very interesting because the bdelloids are also the only major group of animals that has dispensed with sex. Could it be that they were enabled to dispense with sex because they found an alternative way to exchange genes – a sort of reversion to the ancient bacterial way?
I think we can safely conclude that Venter was wrong. Gene exchange among eucaryotes is rare, and certainly much too rare to jeopardise molecular taxonomy." - Richard Dawkins.
It seems strange to me that venter would make such widespread claims when they only apply to a couple of species.
Hah, it’d be funny if Dawkins was correct about that group of organisms eliminating sex due to transfer of genetics in another way. He’s more biologist/scientist than most people give him credit for.
( i know this isn’t on topic but any true biology discussion, especially concerning evolution is welcome here)
I’ve actually had the pleasure of meeting Venter on two separate occasions. They were both very brief encounters, he was pretty in demand as you can well imagine. But seeing how he interacts with people confirms something that pretty much everybody already knows: the guy is an egomaniac. So it shouldn’t come as too much of a surprise that he is given to making rather grandiose claims. It is claims like those that lead to genius when they are borne out, but they are just as likely to be wrong and swept under the carpet.
That said, I think part of it also deals with both where you look on the tree and also what criteria you are using. For example, Bacteria do swap genes around all the time using viruses. Archaea do as well. Now, here is what is trippy, there are viruses out there that can infect Bacteria, Archaea, and Eukaryotes. So while the genetic transfer may be rare, that doesn’t mean it is non-existent and that could mess things up if we define hard-and-fast markers.
Look at Ribosomal DNA. If we just use ribosomal DNA, there are some things included that just plain don’t make sense. For example, I forget their name unfortunately, there is a group of intracellular parasites. If you just look at their ribosomal sequence, you’d place them around Dictyostelium and other very primitive Eukaryotes. But if you look at their genome as a whole, they strongly resemble fungi. So what do we do with that guy?
But I don’t think that is the main take-home lesson here. I think what Venter is trying to say is that some of the ‘points’ on the ToL, such as between Bacteria and Archaea/Eukaryota aren’t really ‘points’ at all, but rather a big blurry mess. As organisms become more derived, these things do start to look like points. But when it comes to really primitive stuff, talking about a common ancestor, it might not make a lot of sense. In that way, Dawkins’ rebuttal can be correct without actually contradicting what Venter is saying.
And it would be cool if bdelloids did work that way. Neat stuff.
Burgess shales in Canada. Cambrian = from Roman name for Wales, Cambria. Classification of rock stratas. English guys in the 1800s came up with those names (e.g. Silurian from Silures, an ancient Celtic tribe, etc.), then the geologist’s classified all the Rock stratas in the world with those names.
Example: the bedrock of eastern Wisconsin is mostly limestone/dolomite which contains invertebrate fossils, like brachiopods (scallop like shells), and they classify it as Silurian. The bedrock of western Wisconsin is mostly limestone/dolomite which contains invertebrate fossils, like brachiopods (scallop like shells), and they classify it as Ordovician. But their basically the same. Some geologist back in the 1800s just arbitrarily said these rocks over here are 400 million years old, wheras these other rocks over there are 435 million years old. Their just numbers in a book. And now their numbers on Wikipedia.
One can find fossilized bivalvia and trilobites, along with fossilized sponges and other fossilized marine life in the same rock strata, but that only shows that the rocks were formed under water.
Haven’t seen to many fossils classified as Cambrian though, except for the museums I have visited. I did view some stromatolites in the Helena formation in Glacier National Park, that they classify as Pre-Cambrian.
