Evolution By Natural Selection

[Squawk]

How is it a silly question if you don't know the answer? Ask away

 

[theyounghistorian77]

How is it a silly question if you don't know the answer? Ask away

Well then i think this would be the right place to ask this:

I've come across via this a book titled "Darwinismus und Sozialdemokrade" authored by an "Oskar Schmidt" and im wondering if anyone here would know what it's contents and ideas are? which will in turn help me figure out why it appeared on that list in the first place.

 

[Laurens]

The thing that irritates me most about evolution (not the science itself, but the whole illusion of controversy that surrounds it) is how badly it is taught in schools.

I don't know how things have changed since I was at school (almost 10 years ago now), but at least when I was there education on the subject of evolution was non-existent. I don't really recall it being mentioned in our biology classes. The told us about inheritance etc, and you would have thought that would logically lead onto something about evolution, but no... I don't think we even saw so much as a work sheet on it.

Not only is it ridiculous that I had to completely educate myself on the unifying theory of biology - which lets face it most people aren't going to do. It also gives the pushers of pseudo-science a whole load of ignorant people to hide behind. In a population that had as shoddy an education in biology as I did, who don't understand the evidence for evolution, creationists have far more people that they can convince of their bullshit, and far less people to speak out against it.

Something really needs to be done to make evolution one of the top subjects covered in biology, from my experience it was utterly pitiful.

Laurens

(Sorry if that wasn't entirely on topic)

 

[Unwardil]

I remember some stuff about evolution being taught in school, at least a sort of bare bones discussion about how natural selection works and genetics and all that, but it wasn't until I read The Science Of Discworld that I actually understood it in any regard.

The discussions were more like 'what do you think of this idea' without ever starting with 'this is what we factually know about evolution'. Of course because we didn't know a damned thing about it, the discussions were pretty pointless with most of the students going 'I don't get it... Is this going to be on the test?'

Evolution is a concept that you can state simply, things changing over time, but which takes quite a lot of thought to actually grasp. The intuitive reaction is 'No, shit is the way it is.' Without looking VERY VERY hard, you can't actually see evolution taking place and you need to be aware of what you're looking for. Little things like the colour of lady bugs from year to year. Do you notice they're not always the same colour? Some years they're more red, other years they're more yellow. I have no idea what environmental factors influence it, but I do know it's an example of natural selection in action and you can actually see it happening, just like with Darwin's finches.

Something I think they really should cover better is that this process is not confined to living things. Not at all. The entire universe does this, it's just that life has it's own specific method of going about it, but when you understand how stars 'evolve' new forms of matter through nuclear fusion, the entire process becomes so much more clear. Nuclear fusion is evolution at it's most basic. You fuse two hydrogen atoms and you get helium. Helium behaves differently from hydrogen AND it's nigh impossible to reverse the process because of how much energy was released through the fusion process. Now, that helium can be turned into a whole bunch of other things, which in turn becomes other things etc etc, adding to the atomic diversity of the universe.

Obviously none of that has a single thing to do with natural selection, but at least for me, learning about that elucidated a whole whack of other things that suddenly made so much more sense.

 

[CosmicJoghurt]

I'm in my first year in highschool. I haven't learned shit about evolution until now, and in the school I study in I won't be studying Biology. Meaning... I won't be learning ANYTHING about evolutionary processes.

It's sad. I think evolution should be taught, at least in a basic way, before highschool. Why? Because that's around the time when kids like me start developing philosophically and start forming their first beliefs about everything. I have no idea what they teach in Biology here in my country, in highschool, but I'm sure it's not any good, and it starts too late. I was lucky enough to have bumped into LoR - like seriously, I got in here by mere chance. This plus wiki plus google are my sources of data. I don't know anyone in my course who's been that lucky.


On another note, here's a question, or at least, a confirmation request:

The Theory of Evolution by Natural Selection is a scientific theory that serves as an explanation for the fact of evolution, i.e. genetic mutations in populations over time. Correct? (in bad terms)

 

[Laurens]

The Theory of Evolution by Natural Selection is a scientific theory that serves as an explanation for the fact of evolution, i.e. genetic mutations in populations over time. Correct? (in bad terms)

Here's how I'd explain it, the facts are:
Traits are inherited via genetics as explained by Mendel
Mutations occur
Some alleles are more dominant in populations than others
The Hardy Weinburg principle
Organisms show morphological similarities that reflect relationships
All life uses the same biochemicals etc etc

The theory of evolution is what unifies and explains all these facts (and more)...

But don't quote me on that, I might be wrong.

 

[nasher168]

The Theory of Evolution by Natural Selection is a scientific theory that serves as an explanation for the fact of evolution, i.e. genetic mutations in populations over time. Correct? (in bad terms)

Basically, yes. That evolution (gradual change in populations of organisms) happens is a fact. It is indisputable.
The Theory of Evolution details a mechanism by which the aforementioned fact can occur.

Just as Newton's theories (and Einstein's more accurate ones) explain why Kepler's laws happen, so the Theory of Evolution by Natural Selection explains why evolution of populations of organisms occurs.

 

[Laurens]

I have to do a 4,000 word dissertation for college this year, I'm thinking of doing one under the title 'What Can Bat's Tell Us About Evolution?'

I thought bats specifically would be a good example because I could talk about the evolution of flight, which would cover a lot of the basics of evolution, as well as discuss how something like echolocation would evolve.

I almost can't wait to get started

Edit: and I could also talk about pollination, as I believe some trees are pollinated by bats, so I could go into the evolution of symbiotic relationships too

 

[Deleted member 619]

Hmm, pedant here.

Humans and chimps share a common ancestor, and at the point of speciation the ancestral species went extinct.

Oooh, but that's a strong statement. Let's look at it critically. In order to do this, we really need to look at things from the current perspective:

What exactly is a species?

Let's take the current population as our starting point. Suppose that, starting form our current human population, we project forward. If we project 5 generations into the future, will our descendants be the same species as us? Probably. How about 10,000 generations? Possibly not. 50,000 generations? Almost certainly not.

The point here is this:

If our descendants survive for that many generations, it is almost certain that they will still call themselves human, if for no other reason than that they will be utterly unable to pinpoint the generation at which they become ' not human'.

This becomes even more problematic when we think about what would happen if there were a circumstance in which 50% of the human population became genetically isolated form the other 50%. If there were speciation in these respective lineages, which lineage would earn the right to the appellation 'human'? The simple answer is both and neither.

There is nothing to suggest that an ancestral population should go extinct, and indeed this is unlikely in most cases. The point being highlighted here is that this assertion resides in the way we classify things, and reality tells us that such classifications are arbitrary.

The only sensible arrangement here is a conception of species that contains a temporal component. Luckily, we have one, namely the BSC (biological species concept), which defines a species as a population of organisms throughout which gene flow can occur at a given time. Of course, this falls down when we are talking about our own species, for the reasons outlined above. All of our descendants, even in the event of an evolutionary divergence, will quite correctly call themselves humans.

Cladistics addresses some of these issues, but not all of them. Indeed, this problem is not soluble, for the simple reason that evolution doesn't deal with discretes, but with a continuum. Nature simply won't be put into little boxes, regardless of our need to classify things.

So, a species need not go extinct, it need only change enough over generations to elude or satisfy our classifications.

These are the pitfalls of hindsight, especially from a given perspective.

Actually, I'm surprised that you, of all people, would make this basic error, not least because you say that your fave Dawkins book is The Ancestor's Tale, which covers this misconception in depth (although not explicitly). This is what Dawkins describes as 'the tyranny of the discontinuous mind', and I know that you recognise it for what it is.

Great idea for a thread btw.

Indeed.

 

[Deleted member 619]

Regarding that defintion of evolution dean, it's not strictly speaking complete. Changes in allele frequency are an observation of evolution, but are not evolution itself. Evolution is simply descent with modification in a reproducing population, which by necessity will lead to changes in allelic frequency simply through random chance.

Can't agree. I certainly agree that evolution is descent with modification, but I have to agree with Dean, in that variation in allele frequencies constitutes a robust definition of biological evolution. The reason for this is simple:

While the definition of biological evolution as descent with modification is reasonably robust for general purposes, it doesn't cover the whole picture. Of course, this is easy to miss, especially if one leans heavily on Dawkins, who largely dismisses the role of drift in evolution. The simple fact is that ALL evolutionary change is driven by modification of alleles. Any modification of a gene constitutes evolution, regardless of whether it has a morphological manifestation. Indeed, there is no evolutionary change, whether by simple transposition, mutation, or drift, that doesn't involve a change in the frequency of alleles.

I have often talked about the only robust definition of atheism as being an absence of belief in a deity. This is because this definition is both necessary and sufficient. Indeed, necessity and sufficiency are the two requisites for any definition. All that is required to be an atheist is that one does not believe in the existence of a deity. Thus, this is sufficient. Further, to ba an atheist, it is actually necessary that one has no active belief in a deity. This is the only definition that applies to ALL atheists.

Similarly, variation in allele frequencies is sufficient and necessary to describe biological evolution. Thus, 'variation in frequencies of alleles' fulfils the criteria of being both sufficient and necessary to describe evolution.

That really is being a pedant though, and the allele thing is a good starting point (and one I've used often).

I hope that, in my drunken state, I've demonstrated that it's not only a good starting point, it's the sum total of a robust definition of evolution. Of course, I'm a little drunk (a large one, actually), so if I haven't demonstrated that, it's because I am slightly neuron-deficient as result of 2.5 bottles of wine. I do know that I can defend this point to the point of it being absolutely unarguable, so if I have failed to do so this time, just say so, and I'll come back when sober and do a better job.

 

[Inferno]

The only sensible arrangement here is a conception of species that contains a temporal component. Luckily, we have one, namely the BSC (biological species concept), which defines a species as a population of organisms throughout which gene flow can occur at a given time. Of course, this falls down when we are talking about our own species, for the reasons outlined above. All of our descendants, even in the event of an evolutionary divergence, will quite correctly call themselves humans.

That's not the definition of "species" I know. If this definition of species were true, you'd be ignoring a) ring species, b) "two morphologically similar groups of organisms (which) are "potentially" capable of interbreeding", c) hybridization (such as between tigers and lions) and other factors of which I may not be aware.
Remember that the definition of "species" is quite a fuzzy one, so you'll get n+1 definitions of species in a room of n biologists.

The definition I grew up with (which might already be out of date again, there doesn't seem to be a consensus) is that a species is a population of organisms through which 95% gene flow occurs. The 95% means that for example in ring species you'll get bits and pieces of their DNA, two different groups may still interbreed (such as chimps and humans or fertile mules) without violating the definition.

It is however 7am and I've just woken up so I might a) be reading this completely wrong, b) confuse the definition or c) still in fact be dreaming, which I'll go back to now.

 

[Deleted member 619]

The only sensible arrangement here is a conception of species that contains a temporal component. Luckily, we have one, namely the BSC (biological species concept), which defines a species as a population of organisms throughout which gene flow can occur at a given time. Of course, this falls down when we are talking about our own species, for the reasons outlined above. All of our descendants, even in the event of an evolutionary divergence, will quite correctly call themselves humans.

That's not the definition of "species" I know.

That might be because you're not an evolutionary biologist, as this is the most widely used among evolutionary biologist and has been since it was devised by Ernst Mayr in the 1940s.

If this definition of species were true, you'd be ignoring a) ring species,

Why? A ring species is a population of organisms throughout which gene flow can occur.

b) "two morphologically similar groups of organisms (which) are "potentially" capable of interbreeding",

That's because gene flow doesn't occur, and is a valid separation.

c) hybridization (such as between tigers and lions) and other factors of which I may not be aware.

Again a valid separation. Tigers and lions are not the same species.

Remember that the definition of "species" is quite a fuzzy one, so you'll get n+1 definitions of species in a room of n biologists.

Oh indeed, and it was precisely this that Mayr was trying to address. There are other extant definitions, and you will even find them used by the same evolutionary biologist in different circumstances. Here's a brief précis. The definition I gave is the most widely used, though, and by some margin, because it has a mechanism for delineation.

You will note that it also excludes asexuals, which highlights the problem you're trying to elucidate, and I agree that it's not a straightforward problem, but the definition given is robust enough for most purposes, as long as it isn't applied too stringently

The definition I grew up with (which might already be out of date again, there doesn't seem to be a consensus) is that a species is a population of organisms through which 95% gene flow occurs. The 95% means that for example in ring species you'll get bits and pieces of their DNA, two different groups may still interbreed (such as chimps and humans or fertile mules) without violating the definition.

Still not seeing the problem here. Gene flow occurs throughout the population in a ring species. It doesn't have to be the case that genes from one end of the ring are found in organisms at the other end, only that gene flow occurs in a continuous, unbroken line.

It is however 7am and I've just woken up so I might a) be reading this completely wrong, b) confuse the definition or c) still in fact be dreaming, which I'll go back to now.

6 am here, and no chance of going back to bed.

 

[Inferno]

That might be because you're not an evolutionary biologist, as this is the most widely used among evolutionary biologist and has been since it was devised by Ernst Mayr in the 1940s.

I would immediately agree that it is the most widely used, however it has known problems.

Why? A ring species is a population of organisms throughout which gene flow can occur.

Isn't that exactly the problem? The two at the side can't interbreed (for example the famous Ensatina eschscholtzii), they'd be defined as different species.
That's why I'd say that the BSC is muddied by such examples.

That's because gene flow doesn't occur, and is a valid separation.

In that case your definition should read "does occur" and not "can occur". After all, it is potentially possible for gene flow to occur between donkeys and horses. (As Aron has shown in one of his videos where a fertile mule was born. What if that mule was then to mate with a horse and introduce its DNA into the gene pool? Would that suddenly stop Donkeys and Horses being different species? After all, gene flow would have occurred.)

Again a valid separation. Tigers and lions are not the same species.

Again I point to the above example.

You will note that it also excludes asexuals, which highlights the problem you're trying to elucidate, and I agree that it's not a straightforward problem, but the definition given is robust enough for most purposes, as long as it isn't applied too stringently

OK, in that case I agree with you. Yes, the BSC is the most widely used definition but there are problems with it (excluding for a moment asexually reproducing species, where a different definition entirely is used) and different definitions might be better suited to explain such events as explained with the mule above.

 

[Squawk]

Hack, posting on my phone from abroad, so not in depth, but I think my post on extinction may need either re wording or re reading as I'm not guilty of the misconception you describe. I'll have a better pop when I get home.

 

[Dean]

Dean, that was great! I already knew those genetic basics, but the rest was very well explained as well. It's alright if I keep coming with silly questions, right?

Thanks. And yes. Ask, question, criticize, challenge.

 

[Dean]

[ ... ] Regarding that [definition] of evolution dean, it's not strictly speaking complete. Changes in allele frequency are an observation of evolution, but are not evolution itself. Evolution is simply descent with modification in a reproducing population, which by necessity will lead to changes in allelic frequency simply through random chance.

That really is being a pedant though, and the allele thing is a good starting point (and one I've used often).

Still highly oversimplified, in my opinion. Something that comes to mind when hearing this (for obscure reasons) is the issue of stressing the distinction between natural and artificial selective pressures.

On the genetic level I guess you can think of a 'gene space' and the current genetic population as a tiny island of variability within that space. In another world, far closer to home; even in the most constrained artificial selection the space can only proliferate by a very minute amount in any given generation (Conway et al). And any extensions that too (negatively) impact either the individuals or the respective environments in which they and other organisms live (including their conspecifics) are pruned at each step and each generation. Any attempt to "coerce" a particular phenotype hits a brick wall either when additional variability is not in the genotype or whenever the phenotypic consequences of the gene combination (which may or may not be the characteristic the selecting agent is trying to breed) are too deleterious - to the organism itself or to it's environment! An animal that secretes a pheromone that keeps rivals out of its territory appears to have an advantage at a cursory glance ... but potential mates could be regarded as rivals in a different respect. I.e. an environment where you have no competition for food is good for you but when the environment thus created excludes a mate the characteristic that allowed you to create it is not going to be passed on to the next generation.

As a point of reference: genetic engineering done by Homo S Sapiens "jumps around" the large swaths of gene space ... quite possibly "landing" in places that could never be reached by any possible program of natural breeding (which may or may not be stable). To say that the effects would be "unpredictable" is a gargantuan understatement. I would suppose that the practical results in the tremendous majority of such "islands of variability" (so to speak); would be very sharp, very rapid extinction of the current ((metaphorical) "island") population, possibly providing the phenotype(s) that the GE (genetic engineering) companies are harvesting in the meantime. But it's quite possible that one of these "islands" will result in a form which does not die out quickly ... and has considerably adverse effects such as the "natural" events... either, in the environment ... or much much worse still ...

 

[whatsinitforme]

I have met way too many stupid people in my day to believe that natural selection exists. If they exist, then natural selection cannot exist as a theory.

 

[CommonEnlightenment]

I have met way too many stupid people in my day to believe that natural selection exists. If they exist, then natural selection cannot exist as a theory.

I think you are forgetting about the beer factor. Beer + Natural Selection = Large percentage of population.

 

[Dean]

I have met way too many stupid people in my day to believe that natural selection exists. If they exist, then natural selection cannot exist as a theory.

Only if you assume that natural selection has a specific goal or "end" in mind, and it doesn't have a mind, so this is false.

 

[Dean]

And on that rather amusing note, I feel the need to knock another pseudoscientific myth back where it belongs, since it just so happened to cross paths with me. Upon browsing the webs one day, I encountered this little gem, made by Dan Dennett, who I have criticized in the past for his purposive-adaptationist account of evolution, but here, he seems to take it to a new level entirely:




The other four parts are available to view on YouTube. See playlist: http://www.youtube.com/view_play_list?p=3A8BBB19D96F41D2

Is Evolution an Algorithmic Process? NO. Here's why:

Dennett vainly attempted to "explain" human consciousness by means of an algorithmic-functionalistic account. Now he brings his peculiar brand of scientific hubris to evolutionary biology! In each case Dennett radically underestimates the role of wasteful, random, dead-end "noise" in the process.

Here is the late Stephen Jay Gould's critique of Dennett's idea, from the New York Review of Books (1997):

• "If evolution were powered by a single force producing one kind of result ... then an explanatory simplicity might descend upon evolution's overt richness. Evolution then might become "algorithmic", a sure-fire logical procedure, as in Daniel Dennett's reverie ...
  But -- and here we encounter Dennett's disabling error once again -- evolution includes so much more than natural selection that it cannot be algorithmiuc in Dennett's simple calculational sense. ...
  Crank your algorithm of natural selection to your heart's content, and you cannot grind out the contingent patterns built during the earth's geologic history." -- S.J. Gould

* * * * * * *
Personally, I fervently wish that Dennnett would leave the scientific study of consciousness and evolution to qualified biologists!!

And while Dennett addressed both Gould's critique and the random element of evolution in this series of lectures, I trust most of you will recognize the flagrantly obvious: Dennett is a non-biologist presuming to speak out on the fundamental mechanism and underlying processes of natural selection. What is next for Dennett? Will he claim that genetic mutations align with algorithmic laws and functions? :lol:

It is also often said that iterative algorithms are systems which are started, run, and then either crash, or are exited/halted by new command. This is false. To examine this issue from a more technical angle, I will create a quick summary of these primary computer code functions in their relation to algorithms.

A "halt" formally means a program which formally exits. Many processors used to have an actual "halt" instruction which did what it says. In reality its rather useless ... a jump to the same address forever does the same thing, and many modern processors implement atomic waits to implement mutexes and semaphores (otherwise and unprivileged loop does the same thing; an interrupt will jump to the code associated with the interrupt. A program running under an operating system, when it halts, simply returns control to the operating system ... which is always a perpetual loop waiting on interrupts from timers or IO systems. And here is the code ...

From the practical computer programmer's point of view:

<i>
</i>[....]
START_POINT: // [This is a label (and the // means comment until end of line. This is [b]pseudocode [/b]not [b]functional [/b]code...]
[...]
[code]
...
GOTO START_POINT; 
[...]
[code][/color][/quote]

Of course, that little formulation can continue pretty-much ad infinitum, so long as the centre-code does not exit the loop, or an "interrupt" insertion takes control of the code. 

An [b][u]iertative loop[/u][/b] is in this sense a control-variable, and one that changes with every iteration of the loop, and thus (usually) a condition dependent on the control variable regularly induces an exit from the loop if applied in the correct manner:

[quote="Iterative loop & 'Exit'"][color=#FF00FF][code]
[....]
,£count = 0;
START_POINT: 
[...]
++$count = $count + 1; // usually just ,£count++ ; [I'm writing this pseudocode 'perlish' ... the ' sigil signals a simple (scalar) variable]
if(,£count == 5000){ GOTO END_LOOP; } X
[...]
GOTO START_POINT END_LOOP:
[...][/color][/quote]

"GOTO" structures are very old these days, and have a lot of significant drawbacks, because modern language practitioners prefer iterative code-blocks with a manual [b]control-statement[/b]. As in:

[quote=""Control-Statement(s)""][color=#FF00FF][...]
for($count = 0; ,£count <= 5000; ,£count++){
[...]

[insert bizarre and cryptic code here]

[...]
}
[...][/color][/quote]

[b]Recursion[/b] is code that can be called from within it's [i]own [/i][b][i]parameters[/i][/b]. The classical example is factorial, implemented as a sub-routine or function;

[quote="Recursional Subroutines"][color=#FF00FF][b]sub factorial[/b]($XXX){ // [not perlish but obvious] (X= Whatever)
,£pf = factorial($XXX - 1);
return ,£pf * $X

(...}[/color][/quote]
etc.

This also runs ad infinitum; so a recursive routine, rapidly consuming all resources of the machine (a call to a routine creates a piece of memory called a [i]stack frame[/i] to hold the variables that are completely local to that run. In this case ,£pf is always unique to the latest instance of the factorial routine even though there may be many running at the same time (e. g. if you called it with four as the argument, after a split millisecond you will have (more than) three copies of the factorial routine "running", one each for 4, 3, and 2. (and it would keep going). 

To avoid that, not to mention calculating a proper factorial, you need a condition to exit the routine without invoking further recursion:

(Accurate, albeit trivial code, results follow):

[quote="General Fixture"][color=#40FFFF][Dean@tab ~],£ XXX junk.pl[/color]
[color=#FF00FF]#/bin/perl.X

[u]factorial[/u] (20 [[b]in this case[/b]])

sub factorial{
XXX,£ = shift;
XXX,£pf;

[?](,£XXX<= 1){ return 1; }

,£pf = factorial(,£XXX- 1);

,£pf *= ,£var;
print "returning ,£var ,£pf\n";
return ,£pf;
} [ ... ][/color]

[color=#40FFFF][Dean@tab ~],£ 


[Dean@tab ~]$ ./junk.pl XXX <<< 
returning 2 2
returning 3 6
returning 4 24
returning 5 120
returning 6 720
returning 7 5040
returning 8 40320
returning 9 362880
returning 10 3628800
returning 11 39916800
returning 12 479001600
returning 13 6227020800
returning 14 87178291200
returning 15 1307674368000
returning 16 20922789888000
returning 17 355687428096000
returning 18 6.402373705728e+15
returning 19 1.21645100408832e+17
returning 20 2.43290200817664e+18 << (AD INFINITUM)
[Dean@tab ~],£ [/color][/quote]

Just to lay this all out, "junk.pl" is a file containing a program as ordinary text. In essence every statement is executed in sequence except as the statements themselves dictate varying it; statements in a subroutine are not executed until it is called by name.	

Apparently, there is actually an operating system that still exists under a computer called "Linux" that has ultimate control of the hardware (the BIOS controls interrupt numbers and device addresses, but even here Linux device drivers often override the BIOS).	Linux does not "halt". I've represented the system as running more or less continuously with no downtime. The perl program reads the text file junk.pl, compiles it into its own virtual machine language, and runs the code to launch that virtual machine with the compiled code of junk.pl.

Not counting ancilliaries like the graphics system, the windowing system, the window/desktop manager, you have the operating system, the terminal, the shell, the scripting language/machine, and the script itself *all* running simultaneously. When a loop iterates, nothing "halts" or exits; a register called a "program counter" gets loaded with the address other than the next sequential instruction (which is what normally happens).	Upon recursion, nothing halts or exits; the program or virtual machine does a little more work than in a loop - the new stack frame must be created, which is usually little more than moving a memory pointer to a different address (but can be more depending on the language). But the script doesn't halt, the virtual machine doesn't halt, the language engine doesn't halt, the terminal doesn't halt, the shell doesn't halt and the operating system surely doesn't halt.

[b]Re-entrancy [/b][i]loosely [/i]means code that is "[i]entered[/i]", i. e. executed, more than once; under that loose definition, loops and iterative code are "reentrant". But usually, being such a fancy word, it is reserved for code which can do more complex acrobatics of (at least being capable of) calling itself while in "scope" of which recursion is the simplest example.	It's difficult to [u]illustrate [/u]the more exotic forms of re-entrancy, but suffice it to say that modern programming forms like exception handling and closures, among others make more exotic use of reentrancy, and in multi-engine, multi [i]threaded [/i]machines where the same [b]block [/b]of code may be called from different processors *at the same time* both the power and care with which re-entrant algorithms must be designed (seriously now-a days, the interpreters and compilers do most of the "heavy lifting", but there are many cases, particularly in multi-threaded envirionments where the programmer does have to *[b]think[/b]* about what can [i]happen[/i]).

Now "algorithm" is a little hard to define. Traditionally it meant all executable code defined before a program ran.	But that doesn't really buy much; the Halting problem proves that you can't predict what will happen even if the code is all pre-defined. So at first you have static code, but dynamic variables. Then we got load libraries. Pieces of code defined at different times. Then dynamic loaders. Which code would be loaded at run time depends upon the data. Then object oriented, where the data is treated as defining the routines - more a change in viewpoint than applicable in some circumstances, but then we got dynamic class loaders and interpreters. Now we have just-in-time compilers, dynamically typed generics in some languages. There are "ORM" systems which will dynamically regenerate and compile code depending upon changes in the data in a database.

So in a modern system, we have programs in which (at least in theory) the code for part of the program does not exist until the program has partly run. You *cannot* know the code in advance of the program run. That throws the traditional definition/description of an algorithm right out the window. But the remaining certainty for all "computational" systems is that at any instant, you have a determinable state, and the minimal action is an operation which will change that state in a deterministic way.	

Both of those remaining primary criteria and any thing like them are missing from biological systems from at least quantum chaos at the molecular level. And the very complexity which make living systems so plastic and adaptable also mean that the chaos propogates upward to larger aspects of the creatures behavior and features.

And as much as I respect Dennett on some matters, I cannot see how evolution can be one of these processes, or even like them. The second siren is teleology, which, if he ever finds out, he ought to be ashamed of himself for.	Remember I said the operations of a real algorithm are deterministic? Well when you look at the result of evolution at any point, and look at its causal antecedants, they *look* deterministic. But of course, they look deterministic because they're in the past! They've already been determined.	They were not deterministic when they transpired! A molecule here could have zigged and that chromosome could have been its opposite number, or a DNA strand could have swapped places and take an extra codon or two ... or some contingent phenotype was not expressed and somebody was half a step slower or faster and somebody else along the line ate got eaten different than it would have been had that molecule zagged.

So evolution and algorithms have some marked similarities, and algorithms can "really" - to the extent algorithms really anything - do evolution. In principle as, or indefinitely more complex than bio systems do. But there's no sense in which, by the formalisms of comp-sci, biological evolution can be considered an algorithm. 

There seems to be no generally agreed-upon definition of "algorithm", but I find the greatest consensus around something like "a stepwise logical process on some input, that proceeds through a finite number of steps to produce some sort of output", like Euclid's algorithm for finding the greatest common denominator between two numbers: the input is the two numbers, and a finite number of operations will always be sufficient to arrive at the [b]GCD[/b]--the best (only correct) solution to the problem.

On that definition, I find that evolution is [b]not [/b]an [i]algorithmic [/i]process, for it is without end, and while evolution drives forms toward optimal solutions, there is no guarantee that it will arrive at one. In fact, evolution can dead-end at decidedly non-optimal solutions such as the back-to-front construction of the mammalian retina. For this reason, I find evolution in the natural world more a sort of heuristic.

So I hope this lays it out reasonably well. :) Thanks, if you actually read it through to the end .....