How likely is human extinction?

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.

Now, now! Don't sell aristotle short. Yeah, he didn't write beautifuk dialogues like plato - but then, who, exept for plato, could? - but the old boy was not a hard-headed blindered type either.

In the eudemian ethics, he quite clearly indicates that the first motion, as it were, of philosophical contemplation is in fact a divinely-initiated one. some averroists even went so far as to say that the whole 'thought thinking itself' business was in fact the divine mind's action through the human intellect (separate matter; save for later0.

Further, in teh nicomachean ethics, and in the politics, aristotle quite clearly shows that the philosophical life is the closest approach to divinity available to man; the political life is a poor, popular reflection of it, and a necessary, but by no means sufficient, precondition for it.

And then there's the whole metaphysics of aristotle; deep, deep waters.

i think people sell the old guy short because his writings seem dry, and because he was a master logician. but remember, that even the master himself described his work as 'organon' - a tool. And he never denied the validity of dialectics.

to sum up: plato - good; aristotle - good. Not pious men (aristotle specifically excludes piety from his list of virtues) but men aware of the divine order of the cosmos nonetheless. (For aristotle, see, particularly the first sentence of the metaphysics: "Man by nature desires to know." one of the proofs of divinity, according to the averroists, was that the creator made man in his image; that is, the universe is, in principle, knowable, because the creator contructed the human intellect in imitation of its own; hence the lucky coincidence between our knowledge and reality. we think, in a way, with the mind of G-d.

Or rather, we once tried, gave up, and here we are now.

Thank you so very much for your interesting post and all the insight! I defer to betty boop for a response on the philosophical issues.

My disagreement with Aristotle is centered on his rejecting existents such as geometric constructs, redness, chairness, threeness, etc. in his sense of "reality".

IMHO, a person's definition of "all that there is" will power (for good or ill) his theology, philosophy and science. If you are interested, here's an article I wrote on the subject:

Evolution through the back door

Well, certainly, a persons' definition of reality will direct his other thinking as well. this is why metaphysics is the heart of the matter.(forgive the philosophical joke.)

we in the west no longer even believe in the possibility of metaphysics, and most people, if informed that at one time the political order was understood to be the human reflection of the order of the cosmos, would regard it as an interesting piece of folklore, on a par with snake-handling, etc.

But, at one time, and for a long time, men understood that the human reflects the divine on every level, even as the Creator's mark and imorint is on all things.

As for chairness, threeness, etc., I must side with Aristotle. a physical entity is what it is because of its form, matter, ends, and particular privation within the matter. some properties are accidents of matter (color, etc.), others are numerical (threeness, etc.), others, such as chairness, are merely a condensed version of the form, matter, ends, and privation which make a chair a chair. furhter, I have always noted that the form, matter, etc., appear to apply to natural beings; artifacts are a whole other category. (Just ask heidegger.)

Thank you so much for your post! Sometimes it seems like you and I switch sides in these discussions, e.g. causation v correlation.

This one feels the same way. I recall your strong advocacy for a variety of number generators which eventually would produce a string representative of any Shakespearean manuscript. If I were to take a Kolmogorov view of any such string, which would be an existent of low complexity under some of the high auto correlation algorithms - I would see a small algorithm, which I would also consider an existent.

Purple, brown, sonata, limerick are all such existents in my view having either a numerical equivalence or an algorithmic equivalence. Though there may be no direct geometric equivalence, they would represent a mathematical structure nonetheless.

At the very least - art and music are information strings which are also mathematical structures. Therefore, in my Platonist view, they exist as such, regardless of their potential myriad manifestations in four dimensions.

But then again, I am Platonist and you evidently are Aristotlean.

Thank you for your always interesting insight!

Thank you so much for sharing your views!

we in the west no longer even believe in the possibility of metaphysics, and most people, if informed that at one time the political order was understood to be the human reflection of the order of the cosmos, would regard it as an interesting piece of folklore, on a par with snake-handling, etc.

IMHO, it is not that people don't believe in metaphysics but that they have substituted "politically correct" terminology to avoid the discussion altogether. For instance, at the point in a physics debate when causation cannot be explained - one might avoid saying "God did it!" by appealing to the "anthropic principle".

Likewise, the plentitude argument (anything that can happen, will/has) is often asserted in cosmology debates to avoid metaphysics. But when countered with the fact of there being a beginning - of time in this universe or many worlds or multi-verse or ekpyrotic cosmology or cyclic cosmology - there is no effective terminology to avoid the metaphysical implication.

This looks to me to be yet another round of the Plato v Aristotle argument. If I am right, donh is taking the part of Aristotle saying that threeness, chairness, redness, pi, good, evil etc. are not existents but rather are useful constructs invented by man to understand the universe.

I know I'm out of my league in this discussion but bear with me. Its not either/or. The two are necessarily intertwined. You can't separate what works from principle, and our imperfect grasp of principle must be forever revalidated against practical reality and our understanding of principle grows as we do.

You can't deal successfully in the material world without discovering and successfully using principles that undergird it. It isn't necessary to get lost in "chairness" to recognize that the physical world operates according to predictable and manipulable principles.

Anyone who deals in this realm, though, cannot help but notice that the principles by which we operate are themselves flawed at the ragged edges. They work 99% of the time, until they don't work, and to cover ourselves we throw in a fudge factor and leave it for the smart guys to sort out why they don't work every time.

That doesn't make these principles a mere "mental construct" unless you choose to define it as such. If by mental construct you mean our best approximation of an underlying principle, then fine, but the reality remains unchanged.

We are human, and our grasp of principles is necessarily imperfect. The principles are good enough for what we are trying to do, most of the time, which makes them a useful tool. That does not make them a useful "fiction", unless you are content to build a fictional chair. People who build real chairs deal with real underlying principles.

The fact that our grasp of the principles is imperfect matters only when our need drives us into the ragged edges, where our approximation no longer works. This is where things get very interesting, because this is the point at which a more profound principle begins to reveal itself. We typically avoid the ragged edges of our approximations as long as we can, because our plate is full just learning what we can do with our shiny new principle. But eventually we are forced to examine those 2% of cases where our approximation doesn't work, and that is where real learning begins. But what we find, inevitably, is not merely a random collection of disconnected datum, but eventually another, deeper, organizing principle. And lots of dandy new projects that become possible once we understand it.

People who argue that there are no underlying principles are enjoying a juvenile sort of contrariness, like taking the losing side in a debate just to prove you can out- argue anyone. We all get annoyed with people who use theory to deny objective reality, and it is always necessary to test our assumptions against reality. And sometimes it is necessary to simply use what works in the absense of any deeper understanding. But with time, and experience, the deeper understanding comes. And the approximations improve as you keep chipping away. Defining our immature, but maturing, grasp of principle as "fiction" does not make it fiction.

You write such beautiful essays, marron! Hopefully one day you'll consider publishing them.

I agree with you in that most people in most circumstances day by day give no thought as to what is or is not an existent and whether a thing is real or an illusion. It is enough that the world continues predictably and mechanistically. In most cases, thoughts of ”all that there is” (however one may understand it) having an organic nature as well only seem to surface in times of reflection or grief.

But some of us are irresistibly drawn to those deep questions most all the time – things like what is all that there is, what is its structure and cause or purpose. Some make a career or profession of it. I believe you are drawn to those kinds of questions as well – because your thoughts run deep and are never dismissive.

What you refer to as an underlying principle I would call a structure of all that there is. I believe we are both looking at the same thing, but from two different aspects. Mine is more math/geometry and thus probably not of much use on these threads but I nevertheless enjoy posting them.

The other difference is that from your aspect the seeking is a journey but from my aspect it is evident that ”all that there is” is profoundly mathematical/geometrical. Therefore, I sense that much of the underlying structure only needs to be discovered and thus I have great and immediate expectations. LOL!

...from my aspect it is evident that ”all that there is” is profoundly mathematical/geometrical.

I also suspect that the principal level of the Universe -- the most fundamental basis of its order -- is profoundly mathematical. The insight goes back to Pythagoras, and was elaborated by Plato.

What is really interesting to me is that many physicists/cosmologists seem to be warming up to Plato in recent times (e.g., Max Tegmark, Attila Grandpierre). It seems that Plato is enjoying a much-overdue comeback! (Yet in Dr. Grandpierre's case, though he beautifully elaborates Plato's Apeiron -- the cosmic Depth of existence -- in the language of physics, he seems to be resisting any acknowledgement of Plato's Epekeina -- the Beyond of the Universe -- which is something that surpasses all categories of understanding in principle. One can understand how a scientist would just naturally resist the idea of something being "beyond" human understanding. Scientists tend to be so optimistic about human capabilities!)

Yet IMO, Platonist that I am, I think we need to keep the Beyond in the picture in order to account for the irreducible mystery behind the universe, and to include the spiritual source of the power that "draws" the Universe and all its living and non-living forms and systems into becoming what they truly are. To expunge it is to perform a reduction of reality down to the level of human capabilities. To me, this is a profound deformation; for man is part of and participant in the universe, not the original power that constitutes and sustains it -- to which Power man and all things are naturally subject.

The Beyond is not an existent among other existents in the Universe; it is absolutely transcendent. But the strange thing about it is human consciousness can experience it, and has been known to do so. I think it's fair to say that the great Greeks -- Plato, Aristotle, Parmenides, Heraclitus, others -- certainly did.

And yes, doesn't marron write simply beautiful, astonishly well-meditated essays?!!! I totally agree with you: marron should get himself published! :^)

Beautifully said, marron. Thank you for your elegant post!

Thomas Heilke notes that "phenomena, the object of the natural sciences, are rooted in physical objects and their relations to one another (force, motion, attraction, etc.). Geometrical descriptions, algebraic formulas, and quantified descriptions are all examples of mathematical expressions pertaining to phenomena. Although anchored in physical entities, they are incidental to the substance or essence of the entities themselves. The appearance of things, presented to the senses, is not their substance or essence, but exists merely at the 'surface of things.'"

[See Heilke, Thomas, Voegelin on the Idea of Race: An Analysis of Modern European Racism, Louisiana State University Press, Baton Rouge, Louisiana, 1990.]

As either Plato or Aristotle would say, the man who wants to know the truth of things, therefore, must penetrate the surface appearance of things. The Greek word for Truth is Aletheia, meaning that which is "unhidden" or "uncovered." For the Greeks, this term has the double meaning of "truth" and "reality." Aristotle's term for the same concept was ousia.

So we who want to know cannot stop with surface appearances -- which in effect are all that physical entities are. Buddhist thinkers took this problem of "surface appearance" to the extreme of calling what we actually see via sense perception as illusion, Maya. In this, I think they go too far. But they do point to a fundamental problem of human knowing. FWIW.

Thanks you so much for writing, marron -- you really do need to get yourself a publisher!!! :^)

Thank you so very much for your excellent, excellent posts, betty boop! As always, I agree with you right down to the last word.

marron, you are blessed with the ability to express deep concepts clearly. That is a most precious gift. I suspect many wonderful ideas are lost to us because the thinker cannot communicate the idea so that others can truly understand. Truly, you should keep all of your essays. Perhaps they will be published someday.

In my opinion, betty boop is above all of us in her ability to find and convey true meanings over all of history and the cosmos. I have asked her to do the same - collect her thoughts - because she must also be published!

You both should see my bookmarks. I try to keep both of your essays, but frankly I'm getting overwhelmed here...

But, at one time, and for a long time, men understood that the human reflects the divine on every level, even as the Creator's mark and imprint is on all things.

Beautifully and truly said, epigone73, IMO. Especially your suggestion that the all-too-fashionable tendency of we "moderns" (post-moderns???) is to reject the insights of some of the greatest thinkers of all time, relegating them to the category of "snake handlers." I don't know how to explain this other than as an exercise in willful ignorance....

As Andre Malraux put it, "the West has begun to doubt its own credentials" -- essentially our inheritance from the classical world and the Judeo-Christian tradition. In their place, we furiously grind out new and better Second Realities.... Which to me are handy-dandy little tricks of mental construction, but not places where a real human being can actually live.

I meant to ping you to reply #374 on this thread, but had an "itchy trigger finger" at the time....

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