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.
That is, at best, a statement of faith. Carl might have gone on to suggest that there is no evidence for anything other than the universe as the sum total of existence, but to turn that into a statement that therefore there is nothing other than the universe would be the fallacy of argument from ignorance. ;)
They were really beautiful in San Diego. Especially right after the sun dropped below the horizon and the sky became an even more brilliant red from the indirect reflection.
It is emminently possible that natural disaster will push humanity to the point of a massive die-off, or even extinction, but lacking that, we are fully capable of destroying our own species, if by no other means than relying on overly-complicated artificial constructs to sustain our population.
Your whole idea is preposterous. More likely the Ozarks. {;^)
...which points to an archai, a beginning orchestrated by intelligent thought. It takes enormous faith to believe in evolution, with its incredibly long timeframes to say nothing of irreducible cellular complexity and even consciousness. There comes a point for every human being, no matter how learned, when he must simply say, I don't know.
I must say, of all the groups I've debated on FR, the evolutionists are the most condescending and bitter, as love and kindness are antithetical to their worldview, all the while arrogantly claiming to be the "enlightened ones". Biological evolution is not proven fact, it is a theory, and a most tenuous one at that. People believe it because they want to, because they can't stand the idea of ultimate accountability to a Creator. Many of the ideas most of us decry here on FR - liberalism, abortionism, socialism, and other "isms" - are justified by their adherents on evolutionary grounds, discussed earlier.
Some scientitsts are to be exempted from this charge as they do not seek to reshape the world ala the U.N., the humanistic Ford Foundation, et. al., and are merely working within the framework they've been taught. It is not against these such polemics are directed.
And yet ... 300 Creationist Lies.
Just as conservative talk show hosts admit their biases and liberals refuse to do so, creationists admit their biases and evolutionists refuse to take their hands off of their closed eyes.
Perhaps. On the other hand, the early inhabitants of the islands might well have been the stone age Guanches people who migrated to the islands centuries before Christ. Indigenous people of the Canary Islands
These early people brought their animals with them but had lost the ability to sail, even from island to island. As a consequence, they were isolated from each other, much like the Galapagos turtles. Apparently, the dialects spoken by the people on the different islands had differentiated into distinct dialects. This may show the evolution of language brought about by isolation I suppose, much like the evolution of differences in turtles and finches.
I'm curious whether DNA analysis could be run on descendants of these stone age people to confirm their supposed Berber origin or an analysis made of their language to see how closely related it was to other languages.
Of course, there might have been Neanderthals on the islands before the Guanches. Have there been any Neanderthal remains found there?
Berbers were the original "Barbarians." Must have crashed too many Roman parties!
The giant Galapagos tortoises are an interesting story. Tortoises are land-dwelling reptiles, and unlike their turtles cousins, they are not adept swimmers. In all likelihood, "giant" tortoises did not raft to the islands. Regular tortoises did. Then, in an island environment, under selective processes, the species evolved from their smaller forebearers.
Just the opposite thing happened on the California Channel Islands over the last 100,000 years. A breeding population of mammoths were able to get out to the islands. (During low sea level stands, the gap between the mainland and the islands was only a few miles wide - and elephants are good swimmers. What caused them to migrate out there is unclear ... predation, abundant food supply, etc.) The fossil evidence suggests that there were no elephant predators on the islands (at low sea level stands the four main islands were connected) and that a process of dwarfing began soon thereafter.
Once on the islands, the elephant population would have been severely strained during times of drought. What type of individual would have survived the stressful times? Ones that had large food and water needs, or the little guys who could get by on less until more abundant years? By the time the last of the mammoths eventually died out, the population was composed of "pygmy mammoths" (now there is an oxymoron) which were less than half the size of their ancestors.
I don't know if there were Neanderthal remains found on the Canary Islands. I was trying to recall something I had read about years before. Your link about the Guanches suggests cultural devolution - an interesting concept.
Evolution of dwarfing in insular elephants
Mammoths survive on island until 2000 BC
I hadn't realized how widespread this phenomenon was or heard of Foster's Island Rule before, but your explanation makes sense.
On the Santa Barbara Channel Islands, a couple of nearly complete skeletons have been found in the dunes. Prof. Larry Agenbroad of Santa Barbara published several papers on these discoveries. The really good find was carbon dated to about 11,000 BC. In the mid-1990's the local geological society ran some field trips out to the sites. Got a few of us desk jockies to do a little field work.
Thanks for the links.
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.