Posted on 12/18/2001 5:07:16 PM PST by Map Kernow
LONG-LOST relatives of the human race have been traced for the first time. They live at the bottom of puddles. A family of humble microbes has been found to carry a special signalling gene that was previously known only in the animal kingdom. The discovery suggests that the single-celled creatures represent a vital staging post in evolution and that all animal life on Earth descended from something very like them.
The survivor from our ancient ancestors is the collar flagellate or choanoflagellate — a microscopic organism that uses a sperm-like tail to swim through shallow water, grazing on bacteria that lodge in its feeding “collars”.
Its remarkable evolutionary legacy, which stretches back at least 600 million years, has been identified by researchers in the US. Today 150 species of collar flagellates exist around the world, but evolution also gave rise to a more complex lineage that eventually led to the animal kingdom.
“They are the closest nonanimal organism to animals,” said Sean Carroll, Professor of Genetics at the University of Wisconsin-Madison, who led the research. “They are to animals what chimps are to humans, and by studying some of their genetic characteristics, we can begin to make some strong inferences.”
In the study, published today in the Proceedings of the National Academy of Sciences, Professor Carroll and his colleague Nicole King analysed proteins from a species of collar flagellate called Monosiga brevicollis. They located a type of signalling gene, receptor tyrosine kinase (RTK), which sends messages to other genes telling them to become active or making them dormant. It is almost identical to similar version found in animals as diverse as humans and sponges.
The findings support strongly the idea that many genes that animals use today were already in place and available on the eve of animal evolution, but changed in function with the step forward to multicellular organisms with distinct body plans and systems of organs.
The microbes, which measure five thousandths of a millimetre in diameter, are protazoans — simple organisms that were once regarded as animals but are now generally considered to be part of a separate kingdom, the single-celled protists.
Scientists consider the moment at which multi-celled animals, or metazoa, evolved from the protozoans to be one of the turning points in the history of life on Earth. The process is thought to have taken place about 600 million years ago.
“The question is, who were the ancestors of animals and what genetic tools did they pass down to the original animals,” Professor Carroll said. The evolution of the metazoa from the protozoans is one of the milestones in the history of life. To build a multicellular organism compatible with a multicellular lifestyle is something that is very difficult. It takes a lot of genetic machinery to do that, and you have to ask the question, did it all arise when the animals came along, or was some of it in place earlier? “We’re starting to get a glimpse of the genetic tool kit we have in common. In choanoflagellates, we’ve found genes that previously were believed only to exist in animals. It’s a confirmation of the idea that the genes come first, before their exploitation by organisms.”
The study concludes: “We have discovered in M. brevicollis the first RTK, to our knowledge, identified outside the metazoa. The architecture . . . resembles that of RTKs in sponges and humans and suggests the ability to receive and transduce signals. Thus, choanoflagellates express genes involved in animal development that are not found in other eukaryotes (complex organisms), and that may be linked to the origin of the metazoa.”
Well, yes. But ... when we observe an event from a distant frame of reference (a supernova will do as an example) it's entirely clear that such event is the result of a causal sequence which is entirely outside of our local sequence of events. This doesn't alter my original statement that the causal sequence of events, moving as it does in one direction, from cause to consequence, underlies our concept of the "flow of time". It's entirely true that we are always getting information from unconnected sequences (that is, from distant frames of reference). Which means that not all events are causally connected (unless you go back to the Big Bang, in which case they are). I still maintain that the cause & effect sequence literally is the direction of and the ultimate nature of time. No causal sequences, no time.
At the heart of your statement lies the question as to which is more fundamental: causality, or time.
My gut impression is that time is the more fundamental property; causality is a consequence of there being time, not the other way around.
Another way to look at this is that causality is a property derived in part from the fact that an order relation can be constructed upon the set of temporal events. The order relation allows us to categorize events into equivalence classes of "before," "after," and "similtaneous" with a given event (in which the equivalence class to which an event belongs is subject to the particular frame of reference from which we observe it and the reference event.)
Without temporal events (time), there would be nothing upon which to construct an order relation which would give rise to our notion of causality. In other words, without the property of "before" and "after" (which are derived from the temporal property) there is no meaningful basis on which to define causality.
Thus, I conclude causality presupposes time, not the other way around.
That said, the two are intimately connected to each other as you have suggested.
You may very well be correct, and it would be folly for me to insist on my interpretation. But as a thought experiment, try to imagine a universe of utterly unchanging and motionless objects, which are not even rotating. There are no causal events in this universe, which means there are no events of any kind. Just existence. In this universe, can you really say that "time" exists at all? I suggest that until things start to happen, which implies causal sequences, there is no time. You can say that time was there all along, just waiting, but I have difficulty understanding what that means. Time without events is like space without matter.
Certainly. It is perhaps not useful for much in your Universe of Terminal Boredom, but that doesn't imply that time doesn't exist, anymore than a lack of racing implies the nonexistence of stopwatches.
I'll go one step further; let us imagine instead a Universe in which there ARE events, but none of them are causally related to any other. (A world of weird sub-atomic particles comes to mind, in which particles wink in and out of existence randomly, and decay spontaneously. A Universe of QM weirdness, if you like.) Clearly, in such a Universe, we could say event "A" occurs "before" or "after" or "similtaneous with" event "B," which implies temporal order, even though there is, by definition, no causality. Thus we can envision a system in which events are temporally well-ordered, yet there is no sense of causality. Clearly, this implies that "time" can exist in the absence of causality, whilst causality can NOT exist in the absence of some meaningful sense of time. This is why I insist that "time" is more fundamental than "causality."
In the end, I must go back to what Einstein said in Special Relativity; that we are part of a Universe that exists in "Spacetime" -- where literally space AND time are interwoven and inseparable elements of the very fabric of the Universe. In this Universe, one literally does not exist without the other. Hence "space" and "time" are the fundamental foundational elements of the Universe, upon which causality (and everything else) is built.
I'll happily defer to our resident Physics factotums on this, in case I've flipped out or have indulged in too many micro-brewed beverages .....
To counteract my Universe of Terminal Boredom, you have proposed a Universe of QM weirdness. Well done. Okay, you've got uncaused events, I'll admit that (based on our current understanding of QM -- if we can call it "understanding"). However ...
There is one cause & effect sequence going on -- that of observing the QM events. As our cosmic observer sees the QM goodies winking and blinking, he experiences the consequences of those QM events. So we do have "time" in a causal sense. Were there no observer, then I would agree that your universe should be as lacking in causal events as mine, and equally void of time -- as I define it. [Three bonus points for using the subjunctive mode.]
So time does still exist, even in the absence of distinguishable events (caused or uncaused). That does not, however, mean that we have events by which we can mark its passage, but with no QM observer to record them, it shouldn't trouble us.
I can go one better, however. One of the canonical solutions to the equations of General Relativity is called de Sitter Space, which is an infinite, eternal expanding universe that is devoid of all matter and energy. It is of course a purely theoretical concept, but it does have space and time. Lately I have seen 5-dimensional Anti-de Sitter space (AdS5) play a key role in some of the weirder extra-dimensional theories being thrown around these days.
longshadow: Well done, indeed; that's exactly the direction I was going with the argument.
Thanks for weighing in on the matter. I was "winging" it, so I though it best to ping you to be sure I wasn't mis-reading where you were headed with your argument.
Ah, but you get extra credit for raising a very insightful question that helps us all fathom the deeper questions of Physics, the Universe, and Everything.
And may you find a well-defined definition of Causality in your Christmas stocking....
Then you'd best get treatment for cancer.
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