Dead-end evolution?

[aviridiane]

I have a sentence here which is rather vague. I do hope someone can shed some light on what's dead-end evolution. I did try browsing through the sites but no luck.

 

Sentence:

Porifera shows 'dead-end' evolution. This means that it represents the end of an evolutionary line.

 

And what does it mean by representing the end of an evolutionary line?

 

Any help is deeply appreciated.

[JHAQ]

That no mutational change confers any further advantage in replication & survivablity ? Class Chelonia is almost in that category due to great advantages of having a carapace .

[Mokele]

Neither are actually represents a 'dead end'; they've found a niche that they work well in, and stick with it, like sharks.

 

A 'dead end' would be like a fruit tree whose name I forget in Australia. It has huge fruit, which used to be eaten by megafauna like giant wombats. But now, such species are extinct, and the fruit has no transport, so it just rots.

 

Mokele

[Helix]

Is it possibe, in theory, to have something be at a "dead-end" in evolution? Isn't there always, some constructive change that can be made? E.g couldn't the sponges evolve to reprodice more frequently?

[Mokele]

Is it possibe, in theory, to have something be at a "dead-end" in evolution?

 

If it can no longer reproduce, as the example I noted, but otherwise, I don't buy the notion of calling something a dead end until it's actually extinct.

 

Mokele

[carol]

I think it is said to have a dead-end evolution because it is believed that no other animals evolved from this group.

[Mokele]

No other animals have evolved from rodents, so are they a dead-end? No other animals have evolved from birds, so are they a dead end?

[aviridiane]

Neither are actually represents a 'dead end'; they've found a niche that they work well in, and stick with it, like sharks.

 

A 'dead end' would be like a fruit tree whose name I forget in Australia. It has huge fruit, which used to be eaten by megafauna like giant wombats. But now, such species are extinct, and the fruit has no transport, so it just rots.

 

Mokele

 

but it isn't extinct or is it? So can a living organism be classified as having a 'dead-end' evolution if it's alive?

 

Or could it mean that the species have evolved to the point at which further evolution is unnecessary as JHAQ wrote, as they are well adapted to the environment.

 

Is there a clear definition on what's 'dead-end' evolution btw?

[Mokele]

So can a living organism be classified as having a 'dead-end' evolution if it's alive?

 

If extinction would be inevitable without human intervention, i guess so. After all, it's not a dead end if it goes extinct; it's just plain dead.

 

Is there a clear definition on what's 'dead-end' evolution btw?

 

I don't think it's actually a legitimate scientific term, so no, not that I know of.

 

Mokele

[carol]

I don't think it's actually a legitimate scientific term, so no, not that I know of.

I think it's a misnomer, and I agree that it doesn't sound like a legitimate scientific term. However, when I encounter that term, it is usually written "dead-end". So, I think they are just trying to give a name for the concept to be easily understood.

No other animals have evolved from rodents, so are they a dead-end? No other animals have evolved from birds, so are they a dead end?

Atm, no other animals evolved from the poriferans, and rodents, and birds too. So, I think they should say all of them have a "dead-end" evolution. I don't know why they don't include rodents and birds.

[Russell]

I stumbled on this thread while I was thinking about an aspect of social Darwinism — specifically the development of concepts of divinity. I think the Taliban constitute a dead-end in this phenomenon.

 

We are told that Joshua leading the Israelites into Canaan roughly thirty-five centuries ago "left none remaining, but utterly destroyed all that breathed, as the Lord God of Israel commanded," — men, women, children and cattle. This same God of Joshua is called upon as "Allah" by the Taliban today. They have reached a dead end in the evolution of religious thought, and are likely to become extinct.

[Ophiolite]

I find the term not just unscientific, but objectionable, since it implies evolution has a direction. However, it is used in respectable journals, both in the sense that the organism is en route to extinction, or that it is merely stagnant.

[Dak]

evolution does have a direction. it's hard to be a driving force without a direction (not a pre-determined one, granted, but evolution still drives change towards a certain end).

 

I always assumed that evolutionary dead-ends were pretty much as JHAQ stated; where there is not only no advantage, but a specific disadvantage, to any change, resulting in evolution maintaining the status quo and preventing any further change. But that was just an assumption.

[iNow]

evolution does have a direction. it's hard to be a driving force without a direction (not a pre-determined one, granted, but evolution still drives change towards a certain end).

 

This is a fairly common misconception, but it's not true. There is no "arrow" of evolutionary change. There is no "direction" and also no "end" toward which it is driving.

 

 

There are countless resources out there supporting my point. Here's one:

 

http://www.talkorigins.org/faqs/horses/horse_evol.html

The "direction" of evolution depends on the ecological challenges facing the individuals of a species and on the variation in that species, not on an inherent "evolutionary trend".

 

 

And another more complete exposition: http://www.talkorigins.org/faqs/evolphil/teleology.html

 

 

Also:

 

http://evolution.berkeley.edu/evolibrary/article/0_0_0/misconcep_02

Because natural selection can produce amazing adaptations, it's tempting to think of it as an all-powerful force, urging organisms on, constantly pushing them in the direction of progress — but this is not what natural selection is like at all.

 

<...>

 

it's more accurate to think of natural selection as a process rather than as a guiding hand. Natural selection is the simple result of variation, differential reproduction, and heredity — it is mindless and mechanistic. It has no goals; it's not striving to produce "progress" or a balanced ecosystem.

Edited April 19, 2009 by iNow

[Dak]

This is a fairly common misconception, but it's not true. There is no "arrow" of evolutionary change. There is no "direction" and also no "end" toward which it is driving.

 

Then what's the difference between neutral and non-neutral evolution?

 

Evolution 'drives' a general tendancy towards an increase in ability to pass the shannon-filter. Evolution therefore has a direction/is a driving force.

 

Terms such as 'increase in fitness' and 'change in allele frequency' over time kinda hightlight the fact that evolution is pushing towards an outcome/one of a limited set of outcomes. [edit]has non-base-chance tendancies towards different outcomes might be a better way of describing it? the outcomes with higher tendancies would be the 'direction'[/edit]

 

Be careful we don't end up having a 20-page semantic argument: 'direction' is metophorical: there is no 'arrow', which is what i was trying to avoid implying by pointing out it's not pre-determined; there is no 'goal', but there is a 'direction'. metaphorically speaking.

Edited April 19, 2009 by Dak

[scrappy]

This is a fairly common misconception' date=' but it's not true. There is no "arrow" of evolutionary change. There is no "direction" and also no "end" toward which it is driving.

Then what's the difference between neutral and non-neutral evolution?[/quote']

Evolution 'drives' a general tendancy towards an increase in ability to pass the shannon-filter. Evolution therefore has a direction/is a driving force.

Dak, iNow is correct: there is no direction to evolution, no progress, no attainment of anything. The fallacy of evolutionary direction was dispatched long ago.

 

And what is this “shannon-filter”? I’m suspecting it’s some kind of imagined entropy filter. Please educate me.

Edited April 19, 2009 by scrappy

[CharonY]

Dak, you are confusing selection as driving force with evolution itself.

[Dak]

entropy filter actually sounds sort of right.

 

the shannon-filter is the selection criteria. In natural selection, the prevalence of an allele is dependant mainly on how well the individuals posessing said allele can reproduce (more or less a tautology: the alleles that can get themselves inherited more are more common). hence, ability to reproduce is the shannon filter. Over time, the ability to reproduce will increase (ability to pass the shannon filter will increase over time).

 

Being able to survive to reproduction age, being fertile, being sexy, being able to look after your offspring, and probably a few other things are all part of 'being able to reproduce'; hence, over time there will be a tendancy for an increase in survivability, fertility, sexyness, and looking after one's offspringyness; to a point, whereafter the higher-than-chance levels will be maintained by evolution (further increases either not being profitable, or the evolutionary forces not being able to overcome the deleteriousness effect of random change)

 

As a thought experiment: imagine rolling 600 die, then re-rolling them: what would be the overall population of numbers (generally, 100 1's, 100 2's, etc).

 

Now, introduce a shannon filter: 'hold' die with a 1/(number showing on the die + 1) probability'. Now, the tendancy over time will be towards a population heavy in 1's, next heavy in 2's, etc up to 'sparce in 6's'. Evolutionary 'direction' here is away from an even spread of numbers towards mostly lower numbers.

 

Which, in a case as simple as this, actually means that evolution does have a clearly pre-determined outcome: there's more-or-less an arrow pointing down a path reading 'evolution goes this way' (as i'm sure a mathematician would confirm)

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Dak, you are confusing selection as driving force with evolution itself.

 

pardon?

[scrappy]

...

Which, in a case as simple as this, actually means that evolution does have a clearly pre-determined outcome: there's more-or-less an arrow pointing down a path reading 'evolution goes this way' (as i'm sure a mathematician would confirm)

Is this your own private theory? Do you have any references to offer in support of it?

[CharonY]

Dak, evolution is the process of change. It is undirected. Imagine that in a given population an allele is exterminated by random even (e.g. genetic drift). You got evolution, but it is not directed with regards to anything.

Natural selection, however, leads to the prevalence of alleles that result in an increase of fitness (by weeding out the others). Hence it is directed (kind of).

[guppyman]

I personally think that there is no such thing as a dead-end evolution.

 

When the planet changes in terms of ecology and temperature, all animals must evolve or die...

[Dak]

Is this your own private theory? Do you have any references to offer in support of it?

 

It was just an observation on my example. there is a predictable and consistant end-result to that scenario, which differs from what would be the case in the absence of a filter. That kinda makes it unavoidable that evolution in that case follows a clear path.

 

Dak, evolution is the process of change. It is undirected. Imagine that in a given population an allele is exterminated by random even (e.g. genetic drift). You got evolution, but it is not directed with regards to anything.

Natural selection, however, leads to the prevalence of alleles that result in an increase of fitness (by weeding out the others). Hence it is directed (kind of).

 

hmm... but, even stuff like the likelyhood of random drop-out due to genetic drift is not entirely random: if an allele is better at passing the filter, it will be more prevalent and thus less likely to suffer drop-out due to drift. It's this overall tendancy away from the base chance level towards something else that i'm thinking of as direction.

 

how, if natural selection has a 'direction', does evolution not, what with NS being a major 'driving force' behind biological evolution?

[Mokele]

Think of a landscape with many hills, and an organism is at a given point in the landscape. NS will ensure that the organism will always move uphill, but only at the local level - if there's another hill nearby that's taller, but the organism would have to pass through a valley to get there, NS won't let it happen.

 

So NS has a 'direction' in that it will always move uphill, but doesn't have a 'direction' in the sense that it has no mechanism to cross valleys or the pick one hill over another.

 

Of course, things are not always so simple - developmental effects can make certain paths unavailable or easier, for instance. But overall, at the very broad, macroevolutionary level, there's no overall pattern or direction.

[Ophiolite]

Dak, you are saying that evolution evolves. Correct?

[scrappy]

I personally think that there is no such thing as a dead-end evolution.

 

When the planet changes in terms of ecology and temperature, all animals must evolve or die...

You might say that a speciation is a kind of dead-end evolution, since every species that ever evolved has or will face extinction. But why even bother with the concept? In 5 billion years all kinds of biological evolution occurring on Earth will be toast...when our biosphere is obliterated by the solar red giant.