Posted on 04/14/2004 6:15:04 AM PDT by Momaw Nadon
Every species seems to come and go. Some last longer than others, but nothing lasts forever. Humans are a relatively recent phenomenon, jumping out of trees and striding across the land around 200 000 years ago. Will we persist for many millions of years to come, or are we headed for an evolutionary makeover, or even extinction?
According to Reinhard Stindl, of the Institute of Medical Biology in Vienna, the answer to this question could lie at the tips of our chromosomes. In a controversial new theory he suggests that all eukaryotic species (everything except bacteria and algae) have an evolutionary "clock" that ticks through generations, counting down to an eventual extinction date. This clock might help to explain some of the more puzzling aspects of evolution, but it also overturns current thinking and even questions the orthodoxy of Darwin's natural selection.
For over 100 years, scientists have grappled with the cause of "background" extinction. Mass extinction events, like the wiping out of dinosaurs 65m years ago, are impressive and dramatic, but account for only around 4% of now extinct species. The majority slip away quietly and without any fanfare. Over 99% of all the species that ever lived on Earth have already passed on, so what happened to the species that weren't annihilated during mass extinction events?
Charles Darwin proposed that evolution is controlled by "survival of the fittest". Current natural selection models imply that evolution is a slow and steady process, with continuous genetic mutations leading to new species that find a niche to live in, or die. But digging through the layers of rock, palaeontologists have found that evolution seems to go in fits and starts. Most species seem to have long stable periods followed by a burst of change: not the slow, steady process predicted by natural selection. Originally scientists attributed this jagged pattern to the imperfections of the fossil record. But in recent years more detailed studies have backed up the idea that evolution proceeds in fits and starts.
The quiet periods in the fossil record where evolution seems to stagnate are a big problem for natural selection: evolution can't just switch on and off. Over 20 years ago the late Stephen Jay Gould suggested internal genetic mechanisms could regulate these quiet evolutionary periods but until now no-one could explain how it would work.
Stindl argues that the protective caps on the end of chromosomes, called telomeres, provide the answer. Like plastic tips on the end of shoelaces, all eukaryotic species have telomeres on the end of their chromosomes to prevent instability. However, cells seem to struggle to copy telomeres properly when they divide, and very gradually the telomeres become shorter.
Stindl's idea is that there is also a tiny loss of telomere length between each generations, mirroring the individual ageing process.
Once a telomere becomes critically short it causes diseases related to chromosomal instability, or limited tissue regeneration, such as cancer and immunodeficiency. "The shortening of telomeres between generations means that eventually the telomeres become critically short for a particular species, causing outbreaks of disease and finally a population crash," says Stindl. "It could explain the disappearance of a seemingly successful species, like Neanderthal man, with no need for external factors such as climate change."
After a population crash there are likely to be isolated groups remaining. Stindl postulates that inbreeding within these groups could "reset" the species clock, elongating telomeres and potentially starting a new species. Studies on mice provide strong evidence to support this. "Established strains of lab mice have exceptionally long telomeres compared to those in wild mice, their ancestors," says Stindl. "Those strains of lab mice were inbred intensively from a small population."
Current estimates suggest telomeres shorten only a tiny amount between each generation, taking thousands of generations to erode to a critical level. Many species can remain stable for tens to hundreds of thousands of years, creating long flat periods in evolution, when nothing much seems to happen.
Telomere erosion is a compelling theory, helping to explain some of the more mysterious patterns in evolution and extinction. There are few data - partly because telomeres are tiny and difficult to measure - but new DNA sequencing techniques could soon change that. Studies have already shown a huge variation in telomere length between different species.
Other scientists are going to take some convincing. David Jablonski, a palaeontologist from the University of Chicago, says: "The telomere hypothesis is interesting, but must be tested against factors like geographic extent, or population size and variability, that have already been proven effective in predicting extinction risk."
Stindl accepts that more experiments need to be done to test his ideas. "We need to compare average telomere lengths between endangered species and current successful species," he says. "I don't expect all endangered species to have short telomeres, since there are clearly other extinction mechanisms resulting from human threats to ecosystems, but I would expect some correlation between extinction risk and telomere length."
If Stindl is correct it will have interesting implications for mankind. Although inbreeding seems to have been the traditional way of lengthening telomeres, there could be a less drastic alternative. Stindl believes that it may be possible to elongate telomeres by increasing the activity of the enzyme telomerase in the embryo. So humans could perhaps boost biodiversity and save endangered species simply by elongating their telomeres. We may even be able to save ourselves when our own telomeres become critically short, making humans the first species to take hold of destiny and prevent their own extinction.
Indicators for human extinction Human telomeres are already relatively short. Are we likely to become extinct soon?
Cancer: Cancer incidence does seem to have increased, but it is hard to say whether this is due to longer lifespans, more pollution, or telomere erosion. The shortest telomere in humans occurs on the short arm of chromosome 17; most human cancers are affected by the loss of a tumour suppressor gene on this chromosome.
Immunodeficiency: Symptoms of an impaired immune system (like those seen in the Aids patients or the elderly) are related to telomere erosion through immune cells being unable to regenerate. Young people starting to suffer more from diseases caused by an impaired immune system might be a result of telomere shortening between generations.
Heart attacks and strokes: Vascular disease could be caused by cells lining blood vessels being unable to replace themselves - a potential symptom of telomere erosion.
Sperm counts: Reduction in male sperm count (the jury is still out on whether this is the case) may indicate severe telomere erosion, but other causes are possible.
If I have my chronology straight, neander presents us with the earliest evidence of tender sentiments, in the form of flowers and keepsakes strewn in graves.
I am more inclined to suspect he was too good for his own smarts.
Human constructs are particularly vulnerable because the critical failure is often something commonplace and taken for granted. The more the technological 'bar' is raised, the more complex the 'basic' components become.
We take telephones for granted, but who could build a pair of phones and power them from scratch, even given the materials? Very few people understand the theory of the devices they use, much less could asemble one.
But it is the cultural constructs which would fail, because they rely on the technological ones. The failing would be man's, not nature's.
Where has it been measured? observed? Repeated? I took a year of paleontology as an undergraduate Geology student. I never saw so manu hypothetical protomorphs and ancestral stocks joined by more dotted lines than the interstate highway system--and that never came close to Humans.
"Evolution" is so full of missing links that it is just a theory, not gospel. Besides, Darwin stole the idea from Wallace, anyway.
"We take telephones for granted, but who could build a pair of phones and power them from scratch, even given the materials? Very few people understand the theory of the devices they use, much less could asemble one."
All taken for granted. I usually use the automobile for this analogy. It has (almost) every modern technology available in it.
Not positive about that but, my tendancy is to agree. There are Neanderthal skeletons found that lived to old age that would have required others to care for it.
My first guess would be: can't interbreed with us.
I find this question kind of interesting. Put the shoe on backwards and consider the discussion about Neanderthal in this thread. Assuming Neanderthal was, in fact, a dead end, how do you think Neander would have felt about, say, our ascending to the moon? Would he feel parental comfort and pride? Would he care at all? How about if he wasn't a dead end, and was, in fact, an ancestor--would that change the picture much?
So do you affirm or deny the proposition that consciousness resides in the hydrogen atoms?
Given the world-view that hydrogen, given enough time, turned into people, the naturalistic world view would require one logically to believe the proposition, would it not?
No reeking intended. TM
Cordially,
hmm. Two for two. Wrong AND irrelevant.
no
your problem resides in the slipperiness of the definition of "resides". This is pretty typical of the absurd knots you can put yourself into by trying to use logic on natural language. You are engaged in what formal logicians often describe as an example of the fallacy of the excluded middle. But I think it's a bit of a strain to cover this case. I'd prefer to call it bait-&-switch.
I'll be more specific. In the first proposition, you want "resides" to mean "requires", for your second proposition have much meat to it. However, your hopes for the acceptance of the first proposition lie in that most people will take "resides" to mean "allows".
Don't do this kind of thing--it damages your brain. Logic is not good for you in your present mind-set--rub more smelly, concrete earth into your brain before you start applying etherial logic to it--if ever.
No. There was quite some discussion of the "fallacy of composition" or some-such-thing last year.
A horse trainer was interviewed on radio last night by, I think, George Noory. The trainer gave his opinion that horses have a high moral sense because they could kill us at any time, but don't because it wouldn't be right. While that may be the case for horses he has trained, or perhaps the trainer is misinterpreting the thoughts of an alien species, not all horses share that sentiment. Many of us have met horses that apparently couldn't stand the idea of humans in their world.
Oh, and aside from being in an illogical syllogism, this proposition is hardly airtight on it's own: the fact that hydrogen turned into people is not particularly pursuasive evidence that outside intervention didn't take place. Whether it did, or not, hydrogen still existed, and was used to make atoms to make humans, presumably. The naturalistic world view is NOT necessarily athiestic. Naturalistic explanations in science do not in any way preclude the possibility of intervention, divine or otherwise. They merely propose that natural explanations are sufficient for most practical purposes of the day. There are those who propose that natural explanations preclude divine explanations, but they are not touting a mainstream scientific line, and they would not be called naturalists by most pedagogically inclined philosophers.
Main Entry: re·side
Pronunciation: ri-'zId
Function: intransitive verb
Inflected Form(s): re·sid·ed; re·sid·ing
Etymology: Middle English, from Middle French or Latin; Middle French resider, from Latin residEre to sit back, remain, abide, from re- + sedEre to sit -- more at SIT
1 a : to be in residence as the incumbent of a benefice or office b : to dwell permanently or continuously : occupy a place as one's legal domicile
2 a : to be present as an element or quality b : to be vested as a right
I took the word "resides" to mean "to be present as an element or quality." In the materialist view, what other choice is there for the source of consciousness other than hydrogen turning by itself over time into people? Logic requires it.
Cordially,
The dictionary does not address the qualities of a thing that may be residing. You do. And you hope the reader will assign two importantly non-identical qualities (must or may), depending on which ox you are goring at the moment.
Yes, but unlike Diamond, they were mostly hysterically-foaming-at-mouth nutcases. But I saw no point in repeating that entire argument when it can probably be easily linked for his perusal.
Then Carl Sagan was not touting a mainstream scientific line when he said in his PBS series Cosmos that the universe is all there ever was or will be. I have always understood the term naturalism (in the philosophical sense) to be the view that there exists nothing outside the physical universe, and that everything that exists, including our own mental states, results from nonrational causes.
Cordially,
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.