How likely is human extinction?

Mail & Guardian Online ^ | Tuesday, April 13, 2004 | Kate Ravilious

[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.

[capitan_refugio]

I think you can inspect the "growth plates" in the bones to determine of the individual was a juvenile. Since I don't know much about elephant morphology, I don't know when they start growing tusks, or how fast the tusks grow. But your pictures sure look like adults to me.

That begs the question, however, whether we are looking at examples of a true "pygmy" or "genetically "dwarved" population, or a stunted individual. I know, in the case of the Santa Barbara Channel Islands, there are enough finds to confirm that the population was indeed dwarved. The oldest mammoth fossils are normal, or near normal, Columbian mammoths. The youngest are all pygmies, and there exists evidence of intermediate types during the intervening thousands of years.

[Ichneumon]

The clincher here is this, if I'm correct in my belief in the book of Genesis, I'll be spending eternity in a field of clover with a cold drink right there whenever I reach for it. Meanwhile, you and your buddies will be stoking a furnace while Asmodeus, Judas Iscariot and Adolf Hitler take turns jabbing you in the glutei with a trident should you stop shoveling for a moment to wipe your brow.

And if you're wrong, Zeus, Odin, and Brahma are going to be really P.O'ed at you.

[Ichneumon]

I never knew that conservative America was made up of so many people who are so desperate to deny God that they stoop to elaborate, unprovable, inimitable and riciculous theories.

If you believe that now, you're still wrong.

First, I've never once met a single adherent to evolution who arrived at that position through "desperation to deny God". Dimensio has done an excellent job of describing how wildly off base you are there.

But even more to the point, you're dead wrong when you describe evolution as an "elaborate, unprovable, inimitable and riciculous theory".

It's somewhat elaborate, like any mature scientific theory (the world itself is not a simple place), but it's hardly "unprovable" (in the scientific sense of the word) nor "ridiculous".

And as for "inimitable", are you sure you know what the word means? Inimitable: "beyond imitation; surpassingly excellent; matchless; unrivaled; exceptional; unique".

[Heatseeker]

The explosion of Toba 75,000 years ago reduced the worldwide population of humans to 2,000 and this event is still seen in the human genetic record.

Sorry to be so late to this thread but caldera explosions are an interest of mine. Actually if worldwide human population were reduced to Bo Derek and me, I'd be OK with it. ;)

[tm22721]

inbred intensively from a small population

All things are relative in West Virginia.

BUMP

[Michael_Michaelangelo]

Creationists have no reason to lie.

And yet ... 300 Creationist Lies.[website posted by PH]

What is *up* with this website you posted? I go to this guy's site and alongside your link is this one:

In PH's defense, I didn't see a post by any Pat or Patrick

[Michael_Michaelangelo]

From the same website:

"The Absurdity of Christianity"

Dang - this guy has some pent-up anger!

[Rebelbase]

Thanks for the Key Deer link. I'll never forget my first glance at a pair of does as zipped down Hwy 1, I thought they were dogs.

[Modernman]

volution attempts to explain existence and life without God.

Sigh. No, it doesn't. If you've read the crevo threads at all, you've probably been told about a million times exactly what the TOE is meant to cover. If you choose to ignore that fact, there's nothing I can do about it.

From this vantage, it is but a small leap to conclude that evolution is loved by those who hate God, by those who know they must one-day answer for every secret deed.

Whether members of your so-called "God-haters" agree with the TOE is completely irrelevant. The correctness of a theory is not a function of the type of person who subscribed to the theory.

Evolution is a theory invented by god-haters

Again, you're either lying or are ignorant of the facts. Charles Darwin was not an especially devout man, AFAIK, but he was not an atheist. What makes you think that biologists, geneticists, paleontologists etc. are any less religious than the general population?

It does not matter what it is called, it is the theory that attempts to discredit the divine truths of Scripture

Only in the minds of religious fanatics does the TOE havr anything to do with religion.

It is little surprise that, in places like the California coast, and New York, where evolution is established dogma, PEOPLE INDEED DO TREAT ONE ANOTHER LIKE ANIMALS, competing for space, food, etc. There is no love, only selfishness

Um, okay. Have you ever been to California or NY? Fifty million people live in those two states. NY and California are pretty much like any other place in the world- there are good people, bad people and people in between.

Your cherished theory deserves much of the blame.

Oh, please.

We will say nothing of Lenin and Hitler here, whose views were thoroughly evolutionary.

So what? Lenin and Hitler also probably believed in the theory of gravity. Does that invalidate THAT theory in your eyes, too?

On the contrary, what do committed, humanistic evolutionists get? An eternity in everlasting fire, where "the worm does not dies" and where the smoke rises forever. Consider this carefully: you'd better be right

Ah, I see. another person who thinks they know the mind of God.

[Modernman]

What is so hard to understand about "Evolution is the theory which best explains the available data?"

It's not a failure to understand, it's a refusal to understand. They seem to think that there is some sinister agenda out there to discredit their religious beliefs.

The funny thing is, people who are secure in their religious beliefs are not threatened by scientific theories.

[null and void]

You haven't seen recent pictures of her have you???

The phrase "plastic surgery disaster" comes to mind...

[Protagoras]

Biological human extinction in the world is 100% certain.

Some will survive permanently in the life after this one.

[Diamond]

That is pretty close to an insane statement. There is nothing remotely "self-refuting" about standing outside a system to describe it. There can be paradoxes and unresolvable statements produced by standing INSIDE a formal system to describe it. Just in general, when we are trying to be careful and/or formal, we put a great deal of effort into making sure were are, in fact, standing outside the systems we try to describe

You are implying that there is something wrong with me noetically. Therefore, you owe an accounting of your notion of the same, an accounting that is consistent with your own presuppositions, because 'standing outside' a consciousness that is wholly a product of material/physical forces that purportedly produce (and continue to produce) the consciousness in the first place, in order to describe it from the outside is impossible.

Either from a purely materialist or naturalist point of view, there can be no rational justification or coherent accounting of the notion, "insane". If my thoughts are nothing but the product of evolutionary, physicial forces then there is no rational basis for anyone to say objectively that there is anything dysfunctional or 'wrong' with my thoughts because my thoughts are nothing but the effect of the same evolutionary, wholly chemical physical/chemical causes that anyone else's are; they are both simply a natural outgrowth of natural processes.

If the logical conslusion lead to absurdity, there must be something wrong with the premise.

Cordially,

[rustbucket]

According to the dates you gave earlier, the downsizing of the Channel Island pygmy mammoths took place over 100,000 years. I saw the figure of 2,000,000 years given for the Mediterranean dwarf elephants and wondered if there were intermediate sized fossils there to show the progression.

If modern humans came out of Africa 100,000 or 200,000 years ago, there would appear to be ample time for people to have developed various genetic differences (e.g., skin color) that gave some small advantage to their possessors. It is too bad that humans didn't invent refined sugar 100,000 years ago, so that we could now eat as much as we want without suffering adverse effects.

I wonder about the origin of human pygmies. Apparently the negroid pygmy found in Africa is also found on islands in the Far East, but I have no idea whether their small size comes from their ancestors having been located on limited-resource islands in the past. The mainland pygmies haven't had time to revert to normal size or else there is insufficient driving force for it to occur quickly.

[Diamond]

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. ;)

Yes, indeed. But that is not what he did.

Cordially,

[Diamond]

...it is not demonstrated that consciousness necessarily had to arise.

True.

We only know that hydrogen was a sufficent condition.

We don't KNOW that.

We do not know that it was a necessary condition, in that, 1) consiousness is not demonstrated to be necessary, and 2) if it were necessary, hydrogen is still not demonstrated to be necessarily needed.

Agreed.

Cordially,

[donh]

You are implying that there is something wrong with me noetically. Therefore, you owe an accounting of your notion of the same,

I apologize if that offended you. However, I do not take seriously the notion that that therefore implies that there is something wrong with you. If I said, "that sentence is ambiguously constructed". or "that does not logically follow". Would you jump to the same conclusion? I am, in my opinion, particularly in this forum, entitled to make critical judgements about statements you make, even if I express them in flowery language.

an accounting that is consistent with your own presuppositions,

You talk funny, cut it out. I respond much better to plain english regarding concrete entities.

because 'standing outside' a consciousness that is wholly a product of material/physical forces that purportedly produce (and continue to produce) the consciousness in the first place, in order to describe it from the outside is impossible.

See comment above. And 1) you started out complaining that the statements in question were "self-refuting" BECAUSE they were statements about science, not from "within" science. Apparently, you want to have your epistimological cake, and eat it too. And 2) there is nothing remotely "impossible" about standing inside a thing (such as, in this case, I guess, consciousness) to describe it. it is done all the time. It is fraught with formal problems--that doesn't mean it can't be done.

Either from a purely materialist or naturalist point of view, there can be no rational justification or coherent accounting of the notion, "insane". If my thoughts are nothing but the product of evolutionary, physicial forces then there is no rational basis for anyone to say objectively that there is anything dysfunctional or 'wrong' with my thoughts because my thoughts are nothing but the effect of the same evolutionary, wholly chemical physical/chemical causes that anyone else's are; they are both simply a natural outgrowth of natural processes.

This is a fairly wellworn creationist dodge--usually applied to morals, rather than to sanity. And just as easily refuted by existence proofs. Despite the fact that there is no reasonably sound evidence of a moral-giving god, or a sanity-giving god, it remains the case that we can easily identify moral and sane individuals based on pure naturalistic, human-useful definitions--which is good enough for government work.

If the logical conslusion lead to absurdity, there must be something wrong with the premise.

Which would be important, if we were seriously engaged in logic here.

And, by the way, this is not a foregone conclusion, there could also be something wrong with your logic. There could also be something wrong with your mapping of a real-world event into a set-theoretic representation upon which logic can usefully work. You may also be working with perfectly correct premises, within a perfectly correct logical system perfectly correctly executed, but the logical system might be inappropriate for the domain of discussion. The abstract notion of "logic", proffered as a defense, is a mighty thin reed to be hanging an argument on, all by itself.

[Diamond]

We will say nothing of Lenin and Hitler here, whose views were thoroughly evolutionary.

So what? Lenin and Hitler also probably believed in the theory of gravity. Does that invalidate THAT theory in your eyes, too?

"At some future period, not very distant as measured by centuries, the civilized races of man will almost certainly exterminate, and replace the savage races throughout the world...

Therefore, here, too, the struggle among themselves arises less from inner aversion than from hunger and love. In both cases, Nature looks on calmly, with satisfaction, in fact. In the struggle for daily bread all those who are weak and sickly or less determined succumb, while the struggle of the males for the female grants the right or opportunity to propagate only to the healthiest. And struggle is always a means for improving a species' health and power of resistance and, therefore, a cause of its higher development.

Tell us then which one was which, of Darwin or Hitler, between the ideological statements above.

Cordially,

[capitan_refugio]

A few years ago I was one of the organizers of Pacific Section Joint Convention of the American Association of Petroleum Geologists, Society of Economic Paleontologists and Mineralogists, and the Society of Petroleum Engineers. (What a mouthful - that's why they use acronyms!) The late Professor Pete Weigand at Cal State Northridge edited one of the two volumes from the convention which included a good short article by Dr. Larry Agenbroad, entitled "New Pygmy Mammoth (Mammuthus exilis) Localities and Radiocarbon Dates from San Miguel, Santa Rosa, and Santa Cruz Islands, California." The radiocarbon dates for Agenbroad's spectacular M. exilis discovery were reported at 12,840 +/- 410 B.P. The importance of this 1994 discovery was that the skelton war nearly complete and that it was clearly in a "primary depositional context." These were also the last of the mammoths on the islands. Scattered remains are probably re-worked, so accurate dates for the fossil can not be obtained from the surrounding strata, but only from the fossil itself.

One recently discovered site yielded an "intermediate form" (somewhat larger than the other M. exilis specimens) dated at 47,110 BP. Uranium-thorium dates have been acquired on mammoth teeth from Santa Rosa Island report 68,000 +/- 4,000 BP, 64,500 +/- 7,400 BP, and 29,000 +/- 2,000 BP. However, these dates are suspect. I once suggested using the amino acid racimization dating technique that had been used on marine mollusks, but who listens to me?

[donh]

.We only know that hydrogen was a sufficent condition.

We don't KNOW that.

Well, really, we do. We do not know that it is THE sufficient condition, but we definitely know it was A sufficient condition. Once again I have to caution you that natural language and logic are fairly incompatible per se. natural language is freighted with hidden assumption that, when properly mapped out into venn diagrams, turn one sentence into many formal suppositions.

In this case, I'll take a stab that the unstated supposition is that consciousness is necessary--it may not be. It might the the shearest of flukes. If it is necessary, and it's occurance from random chance unlikely, than you have an argument for a second condition, other than the existence of hydrogen.

So, what you have here, is a subtle application of post hoc, ergo propter hoc reasoning. You assume (or at least, hope to bring to the table) that consciousness is necessary (it's arising from chance events unlikely), when you make a case against the notion that the existence of hydrogen is a sufficient condition.

It is A sufficient condition, and we know that without serious doubt. It may or may not be the only one, but for a philosophical naturalist, it's sufficient to work with to answer the day's needs, and that's the naturalist's important yardstick. It is not a measure of ultimate truth, and the naturalist is not gainsaying other causes/conditions. The naturalist merely asserting that he wants to work with ideas that are proving useful, and eschew ideas that seem to be superfluous, whether they are true or not.