Question about evolution

[Kilted]

Hey there all, just have a question about evolution thats been on my mind for a while.

Ok i understand how evolution works on a basic level - genetic variation leads some animals to be able to take advantage of their environment better than others, and so are more likely to reproduce than others not so suited. Ok i know thats really basic but its not that that i have a problem about.

Im wondering about the formation of a system (such as the respiritory system - that relies on more than one componant part working alongside others. for example for the respiritory system to work, you need to have an airway, and a way for oxygen to get into the blood, something to pump the blood to all the cells, and so on. so would all these systems have to have evolved at once since they all need each other to work? And is this what people mean when they say irreducible complexity?

Sorry if this is in the wrong forum, i just think its more sciency than paranormal or anything :)

[Phil]

Yes, that is what people mean when they say 'irreducible complexity'. The system is such that to reduce it by even a single component would be to render it useless.

I'm no expert, but the parallel I've always heard referred to is the formation of the eye. Certainly without one component of the eye as we know it now in place, the capacity for vision as we know it now would be gone. But even a membrane that detects light and shadow is an advantage for a species that never had it before. And it's my understanding that eyes could have evolved piecemeal in this manner.

Someone who knows better please correct me.

[The idea]

Originally posted by Kilted
Im wondering about the formation of a system (such as the respiritory system - that relies on more than one componant part working alongside others. for example for the respiritory system to work, you need to have an airway, and a way for oxygen to get into the blood, something to pump the blood to all the cells, and so on. so would all these systems have to have evolved at once since they all need each other to work?
Are you sure that a specialized airway and something to pump blood are essential? Are you sure that simple diffusion won't work for simple multicellular organisms?

What is the alternative to "evolving at once"? For thousands of generations almost all of the genetic code of a species stays constant and changes take place only in the part of the genetic code that is associated with one component of one system in an organism of that species?

[Alkatran]

Yes, that's called irreducile complexity. It's the "best" argument IDers have (note that it's not even an argument for them, but an argument against evolution).

The argument is flawed because it assumes you can't remove pieces and that there is no 'simpler' version of anything that could do the same function (providing energy to cells in this case).

[The idea]

Originally posted by Kilted
[...] for example for the respiritory system to work, you need to have [...] a way for oxygen to get into the blood [...]
Organisms around the world have been heard chanting not just "four legs good, two legs bad," but also:

"Blood for oxygen, not for oil. Blood for oxygen, not for oil."

It might have something to do with Iraq.

[Jon.]

Kilted,

There is an answer to your question. Unfortunately, it is too long and complex (irreducibly complex? ;) ) to be put into a post and done justice. If you are interested in this area, get a good book on evolution. I would suggest The Blind Watchmaker by Richard Dawkins. He takes on the irreducible complexity argument quite nicely.

[Kilted]

ok so the heart, lungs etc would have evolved from simpler and simpler structures? and thats why they all work in tandum? so any further evolution would just make improvements on whats already there?

ETA cheers Jon i might well do that if i can find a cheap copy

[Jeff Corey]

Kilted,
I would reccommend R. Dawkin's The Blind Watchmaker or S.J.Gould's The Panda's Thumb for more authoritative and well-written explanations, but consider that humans and pigeons have color vision, unlike a majority of other animals. They both have specialized receptors in the retinas at the back of their eyes that respond differently to different wavelengths of light. They both have lenses to focus images on the retina.
But in humans and other great apes, the retina is inverted - the receptors are pointed away from the stimulus.
In pigeons, it isn't.
How can that work both ways?
In apes the sclera reflects the image back into the cones.

[Bronze Dog]

Originally posted by Kilted
so any further evolution would just make improvements on whats already there?
Evolution doesn't guarantee improvement: If it survives long enough to have kids, it's good enough for evolution. But I'm sure you probably knew that.

[Ashles]

I was going to post this in a new thread, but I think it fits in well here.

Why do animals age?

I understand the development of creatures to maturity is vital for many reasons, but as far as I am aware aging functions are gentically controlled.

Why hasn't any animal evolved that just wouldn't age past a certain point?

Surely it would be immensely selected for?

This is one of the things I don't get - if something as complicated and utterly useful as vision or flight can evolve, why not something that merely requires certain genes be turned off at certain times?

I'm sure I am missing something here but would be interested in knowing what.

[Seismosaurus]

Originally posted by Ashles
I was going to post this in a new thread, but I think it fits in well here.

Why do animals age?

I understand the development of creatures to maturity is vital for many reasons, but as far as I am aware aging functions are gentically controlled.

Why hasn't any animal evolved that just wouldn't age past a certain point?

Surely it would be immensely selected for?

This is one of the things I don't get - if something as complicated and utterly useful as vision or flight can evolve, why not something that merely requires certain genes be turned off at certain times?

I'm sure I am missing something here but would be interested in knowing what.

At a guess...

It would make the species as a whole less adaptable. As noted earlier, evolution happens because you pass on your successful genes by having lots of offspring. But if a species was essentially immortal, the offspring would never survive - they'd be competing with their parents for resources. So any beneficial mutations would never get a chance to take hold in the species.

Like I say, just a guess.

[Bronze Dog]

Originally posted by Seismosaurus
Like I say, just a guess.
And it sounds like a good one to me.

[Ashles]

Originally posted by Seismosaurus
At a guess...

It would make the species as a whole less adaptable. As noted earlier, evolution happens because you pass on your successful genes by having lots of offspring. But if a species was essentially immortal, the offspring would never survive - they'd be competing with their parents for resources. So any beneficial mutations would never get a chance to take hold in the species.
But surely that wouldn't matter. They could still die of all the normal external factors and Natural Selection would still apply to those more mundane characteristics...

And once the genetic code for 'immortality' was there I don't see how it would ever be selected against.

And that leads me to another question about Natural Selection - surely there are ecosystem unbalancing mutations - mutations that would convey such a colossal advantage to a species that it would irreversibly be selected for to devastating effect (but maybe that is currently being expressed through man's intelligence and problem solving abilities).

Don't get me wrong - I think Natural Selection is almost certainly the correct mechanism - there's just a couple of wrinkles I don't quite get.

[SezMe]

Originally posted by Ashles
This is one of the things I don't get - if something as complicated and utterly useful as vision or flight can evolve, why not something that merely requires certain genes be turned off at certain times?
I don't think that turning on or off certain genes would halt the aging process. For example, background radiation is constantly affecting our bodies, degrading our DNA. Additionally, when cells divide, the DNA replication process may not be perfect, leading to further degradation.

I am sure there are numerous other purely physical factors that cause aging that no amount of evolution can overcome.

[Dymanic]

Originally posted by Ashles
Why hasn't any animal evolved that just wouldn't age past a certain point? Originally posted by Seismosaurus
At a guess...

It would make the species as a whole less adaptable
At first glance, that seems like a not altogether unreasonable guess, but there are several reasons to give rather more weight to some other guesses.

We might consider a hypothetical population in which individuals all (through some kind of 'planned obsolescence' gene) made such a sacrifice of years of longevity in order that their species as a whole would benefit from the resulting increased availability of resources. But consider how vulnerable such a population would be to being quickly overrun by the progeny of a single 'defector' organism who, lacking this gene, made disproportionately large contributions to the population by going extra breeding seasons.

The main thing is to keep in mind that the design features of a biological organism represent a balance between factors; often opposing factors. For example:

When food is plentiful and easy to obtain, raising the largest possible broods of offspring may be the best strategy for long-term reproductive 'success', even if the offspring are weak and stupid. Where it is scarce, better equipped offspring may be the way to go -- but special equipment like sophisticated brains, eyes, and wings take embryonic time to develop, and learning how to use them often renders the young relatively helpless during the training period, which means they require more parental care, which means smaller broods (except it doesn't necessarily mean broods have to be smaller, just that allocating developmental resources to larger broods will tend to be wasteful, as most will die anyway).

The viability of eggs declines with age, and the supply is limited to begin with (a rule of thumb in biology is: "eggs are expensive, sperm is cheap"); in human females, for example, the rate of egg depletion doubles at about 37, and by about age 50, is typically exhaused entirely. It may be that changes to some genes might improve these numbers, but as with everything else, there will be a cost.

The question, then, really is: what is the potential reproductive payoff, for the individual of greater longevity, and what are the costs -- and how do those payoffs and costs compare to the payoffs and costs of giving priority to other factors?

[Eos of the Eons]

I'm not sure what determines the aging rate. Humans live a long time compared to most other animals, but our young also need a lot of care for longer as well.

Lesse. Every cell in your body is as old as you are. Cells that replace others have been made by spitting a cell in two, a cell that is just as old as you are. There are no "new cells" for your brain, skin, etc. Blood cells are made by cells that are as old as you are, replacement cell division slows, some mistakes start to happen...
Human telomeres consist of chemical clusters called "base pairs" that are strung together in a specific sequence known by the initials TTAGGG. This sequence is repeated several thousand times along the length of the telomere. But each time a cell divides during its normal life cycle, its telomeres are shortened by about 100 base pairs until all cell division finally comes to a halt.


"In order for a cell to become cancerous, one of the things it has to do is switch on the telomerase gene which makes the telomeres longer," he said. "The body has decided that the best way to keep an organism alive is to keep telomerase turned off, because otherwise you can get mutations and cancer too easily."

http://www.obgyn.net/newsheadlines/headline_medical_news-Cell_Biology-20021225-2.asp


...That first cell can divide 50 times before it reaches its Hayflick limit and will be destroyed. This is determined by little "caps" on the ends of the chromosomes called telomeres. Telomeric DNA protects the genetic material that codes for traits from being dropped off the ends of your chromosomes each time they divide. It is noncoding DNA that is repetitive.

...Eventually, it is hypothesized, there will reach a point where all the cells are getting olderand the original cells aren't replacing the dead ones as fast or there aren't as many around to replace the dead ones. This is what happens as we age.


http://www.newton.dep.anl.gov/askasci/mole00/mole00615.htmIn recent years it has been found that the number of population doublings of which cultured normal cells are capable is inversely proportional to donor age. There is also good evidence that the number of population doublings of cultured normal fibroblasts is directly proportional to the maximum lifespan of ten species that have been studied. Cultures prepared from patients with accelerated aging syndromes (progeria and Werner's syndrome) undergo far fewer doublings than do those of age-matched controls. http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=3913498&dopt=Abstract
It seems as the rate of replication slows, we see signs of aging when cells are around longer and dying off before daughter cells take their place?

So, there needs to be a balance. Replication rates need to be controlled to prevent cancer, (too much growth/replication too fast anywhere would be disasterous, etc.) Yet a too slow replication rate will result in more rapid aging.

http://www.obgyn.net/newsheadlines/headline_medical_news-Cell_Biology-20021225-2.asp

[Eos of the Eons]

Respiratory System...
To see the evolutionary adaptations of taking in gasses, you'd have to start with water creatures. It's a rather in depth look of what is needed to be built upon to get to land creatures.

Then you have to look at the role of breathing and metabolism. Then you have to look at blood circulation, bonds, etc. Metabolism is also tied into ingestion. Everything did evolve *together*, so you can't take away one piece at any time. You will find all plants and animals have some kind of system for the intake of gasses and nutrients. The systems get more and more sophisticated as the organism gets more complex. That doesn't make one system "better" than another, just essential for that type of organism to be alive.

It would take months to explain everything. Just take some zoology courses in college...heh.

[espritch]

ok so the heart, lungs etc would have evolved from simpler and simpler structures? and thats why they all work in tandum? so any further evolution would just make improvements on whats already there?

It's not always that simple. Sometimes structures evolved for one purpose are latter adapted for a completely different purpose. A good example is the lung. Lungs probably started out as swim bladders. Most bony fish have sacks containing air that they use for bouyancy control. Fish that live in low oxygen environments will often swallow air from the surface to refresh the air in the swim bladder so they can absorb additional oxygen to supplement their gills. The "lung" of the lung fish (if I recall correctly) is just a swim bladder adapted for use as a simple lung.

Modern frogs and salamanders breath with lungs as adults but use gills in their larval stage (it that the correct term for a polywog?).

So the lung was adapted from a structure that wasn't evolved for breathing at all.

[Eos of the Eons]

Not only that, but there is always moisture involved in respiration/transpiration no matter if you are plant or animal.

Hmm, how do bugs "breath" again? Argh. I forget. I know it involves spiracles, but uh, bugs always seem very dry...

But still, moisture is mentioned in beetle respiration:

http://www.desertmuseum.org/books/nhsd_beetles.html

The cavity beneath the forewings serves as a site for the storage of oxygen in aquatic species, while insulating desert-dwelling species from the heat and minimizing water loss through respiration.

[espritch]

Hmm, how do bugs "breath" again? Argh. I forget. I know it involves spiracles, but uh, bugs always seem very dry...


Only on the outside. They are quite gooey inside (just like us).

[Dylab]

I think I remember reading that animals that are more likely to be eaten by a predator or killed prematurely by some other means tend to live shorter lthan animals that have a smaller death rate. This would suggest that aging is a tradeoff for improving your fitness in youth since living old is a waste if you are going to get eaten anyway.

Williams was the one who came up with the idea "pleiotropy" that the negatives effects of aging evolved as a byproduct of genes that were more advantagous for youth.

[Eos of the Eons]

Originally posted by espritch
Only on the outside. They are quite gooey inside (just like us).

Oh yeahhhh...ewww, :D

Those exoskeletons sure offer an advantage in rough areas to live though! But not very flexible. Flip any beetle onto its back and watch it freak out...

[pmurray]

Originally posted by Ashles
Why do animals age?

Well, there are plenty of unicellular animals that don't - amoeba are effectively immortal.

There are indications that sexual reporoduction is an adaptation that repairs cellular damage. Perhaps one strain of organisms started doing it all the time, rather than only in response to damage, and the immortalitiy thing became an unnessesary burden.

In any case - "why" is a meaningless question if it is asking for a reason rather than a cause. Nature is what happens - the precise error that science answers is the idea that nature fits our verbal stories of it.

[SixSixSix]

Casting the question another way: why don't we age faster? Most things eventually break down; entropy will finish us even if we manage to survive the Sun going supernova.

Over a long enough time period everyone's life expectancy drops to zero; even if you didn't age, you'd be eaten by something/run over by a truck/whatever. While it is efficient for an organism to resist aging for a time, it is pointless to try and resist it forever (and note that I'm using words like "try" here anecdotally only; natural selection is not the result of intelligence, and has no goals - it's just that it is convenient to talk about the emergent complexity as if it did). An organism that possessed a mutation that would allow it to live 10% longer might require 11% more food than the baseline species and leave fewer offspring despite their longer life.

Basically, it is reasonable to suppose that we live as long as we do because that's the sweet spot where things are balanced. And of course one could also argue that with possible future advances in gene therapy that lead to longer lifespans we are evolving to live longer - if not by strictly "natural" selection.

[MRC_Hans]

Originally posted by Kilted
ok so the heart, lungs etc would have evolved from simpler and simpler structures? and thats why they all work in tandum? so any further evolution would just make improvements on whats already there?

ETA cheers Jon i might well do that if i can find a cheap copy There are numerous examples of simpler respiratory systems.

Earthworms have blood (it is even red), but no lungs, they absorb oxygen through the skin, and no heart, their movements make the blood circulate.

Snails have a simple lung (really just an air sack), but still no heart.

Insects have (a sort of) lungs, but no blood circuit. Instead they circulate air directly to the tissues needing oxygen.

Frogs have both lungs and heart, but some can also survive breathing through the skin.

So, respiratory systems are far from irreducible.

So if we want to hypothezise on how one could have evolved, it could be like this:

A strain of earthworms have a group of muscles that can circulate blood without the worm moving. This enables them to colonize an environment where the ability to lie still and be ready for action (perhaps hiding, and fleing from, predators) is an advantage. So the better these muscles work, the better survival. So now it has a form of heart. Next a strain with folds in the skin can absorb more oxygen, thus has more energy available for faster movement. Lungs have begun to evolve, etc. etc.

The important point is that each change must be, if not an advantage, then at least not a disadvantage.

Hans

[Soapy Sam]

The hardline reductionist answer to why do animals age is that the question addresses the wrong biological level.

Species come and go on a million year cycle.

Individual animals come and go on a lifecycle of millennia ( Bristlecone Pines), centuries (trees, some lichens, elephants, humans, large birds), years (most things) , months (many cells) and so on.

How long do genes last?

In theory, sex can mix them up after one generation - but the evidence is mounting that there are gene sequences in existence now, in humans and other creatures including plants, which are identical to DNA sequences which existed hundreds of millions of years ago.

We conclude this by inference, because there are only so many ways to do certain things at a chemical / physical level.
There is a limited number of ways for any organism to photosynthesise for instance. There is a limited number of ways for an organism to produce and use ATP.

There are many chemical processes which are fundamental to life, which have been there from the earliest of life forms we can detect and which have been used again and again throughout the evolutionary story. These processes are controlled by the same mechanisms, produced by the same proteins, created by the same RNA, coded for by the same DNA.

DNA is forever*. It's not "immortal", because it is not alive. And it doesn't give a toss if you die at thirty, so long as you reproduce at twenty.


*For a certain meaning of "forever".

Ironically, what this means is that some DNA does not evolve at all. It's the DNA survival machines (us) that do the evolving, to keep up with changes in the environment- including competition from other DNA survival machines.

An immortal machine would be useful to DNA only if it was also flexible in its immortality; if it was able to stay alive (and keep reproducing) , by constant adaptation to environmental changes.

Does this remind anyone of anything at all?

[SezMe]

Originally posted by Soapy Sam
An immortal machine would be useful to DNA only if it was also flexible in its immortality; if it was able to stay alive (and keep reproducing) , by constant adaptation to environmental changes.

Does this remind anyone of anything at all?
The Discovery Institute? :)

Sorry for the derail...carry on.

[RandFan]

Originally posted by Eos of the Eons
Lesse. Every cell in your body is as old as you are. Cells that replace others have been made by spitting a cell in two, a cell that is just as old as you are. Yes, but an old man like Tony Randall (now dead) can produce offspring with young cells. Why can't our bodies regenerate young cells the way we can reproduce offspring? The cells in my body can be traced back to the very first Human and even to one of the very first if not the first single cell organism. Also, telomeres (http://universe-review.ca/R10-31-ageing1.htm) are a like a genetic, biological clock that effect aging.

See Ageing (http://universe-review.ca/R10-27-ageing.htm).

Telomeres are discussed about half way down.

[Orangutan]

Originally posted by Ashles
Why do animals age?


I have just started reading "The Selfish Gene" (Dawkins) And I think it has something to do with the fact that the animal is just a vessel for passing and replicating the Gene. As long as we can do that we have serverd our purpose.

It reminds me of an engineer wh said the perfect formula one race car would fall to peices as soon as it crossed the finish line. (anything else would be over engineering and a waste of resources).

So like our inverted eye structure, as mentioned earlier, it may not be the best design that we die (for us anyway), but it is perfectly acceptable for a gene who only needs to keep making it to the next generation.

So basically we die because it benifit's our genes.

O.
:)

[Soapy Sam]

Exactly. Except that there is no "purpose".

[Badly Shaved Monkey]

Originally posted by pmurray
Well, there are plenty of unicellular animals that don't - amoeba are effectively immortal.


Could genome size matter? Perhaps a simple genome can be kept clean and tidy for very long periods, but maybe you can't have a genome as complex as ours with so much gene switching on and off and selective expression in different tissues without the whole thing getting gummed up eventually.

Which leads to...can an organism with differentiated organs and tissues be immortal or is immortality a single-cells only club?

What I'd like to know is whether the adaptive function of our shortening telomeres is 'intended' to limit our llifespans or do they shorten for some other reason, i.e. is this process evolved to be the clock on our lifespan or does it serve sopme other function with the limitation on our lifespan being a secondary consequence.


Originally posted by RandFan Also, telomeres are a like a genetic, biological clock that effect aging. [/B]

I think that was a typo, but a fortuitous one: do telomeres effect ageing or merely affect it?

[Orangutan]

Originally posted by Soapy Sam
Exactly. Except that there is no "purpose".

Your right, in that purpose suggest some deliberate descision making on the part of the gene. I suppose it would have been better to say:

"As long as we can do that [reproduce] we have done enough to allow the type of animal our genes make us, the type that eventually dies, carry those genes on for another generation."

lol.