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OptimisticCynic

Evolution Without Pressure

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Delta1212, Nice coverage of how selection pressure works.

 

Now, thanks to the help of all of you, I can see this evolution pressure thing from a different angle. This view is really cool and deals with your questions too.

 

Many variations in genotype occur regularly and repeatedly but only succeed in surviving to reproduce when a selection pressure that previously eliminated them disappears or is greatly reduced. The same or similar variants are widely dispersed in the original population. Variants may self concentrate and then interbreed. This can result in further exaggerating the variation that brought them together. When the pressure returns, the exaggerated variants may now be able to withstand that selection pressure. The less exaggerated variants are eliminated. What we see later, in times of higher pressure, is the originating population and the exaggerated variants in their separate situations. The necessary degree of variation may only arise when the selection pressure(s) that culled the minor variants drops low enough that the minor variants can survive long enough to concentrate and produce the more exaggerated variants.

 

O+O produce offspring O,O,O,A at habitat or food source Q

A migrates to a habitat or food source better suited for it or with less competition from the original population. ---ONE---

Pressure P kills A

The pattern repeats until...

A survives because some external event removed pressure P ---TWO---

O'+O' produce offspring O,A',O,O

A' migrates to its preferred habitat or food source, H

A meets A' at their favorite place. ---THREE---

A+A' produce offspring A,A',O,A"

O migrates to its preferred habitat or food source, Q

A,A',A" stay at their preferred habitat or food source, H

A,A',A" produce more offspring.

A"+A" produce offspring A^ ---FOUR---

P returns

A, A',A" and O located at H are eliminated by P

A^ survives and reproduces ---FIVE---


One -- migration to preferred situation

Two -- reduced or eliminated culling pressure

Three -- concentration of variant genotypes

Four -- exaggeration (or combination) of characteristics

Five -- exaggerated characteristics enable survival of returned (or new) culling pressure

Edited by OptimisticCynic

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One area of pressure related change is domestic dogs. The Australian Cattle dog, the Belgian Malinois, and the American Pitbull have all appeared in separate places on the earth, over the past about 100 years, due to each having a low pressure; cuddled, environment that allowed each to differentiate. If these three dogs had appeared naturally, we would have attributed this to evolution. It shows what can happen if we selectively reduce the pressure. Humans merely speeded up the process with an exaggerated cuddle.

 

This is loosely analogous to time/temperature testing of plastics, where exaggerated parameters of temperature, allows us to predict, longer term properties, like 25 year plastics, in a few hours. Domestication did in 100 years what nature may take thousands, via concentrated cuddle time testing.

Edited by puppypower

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One area of pressure related change is domestic dogs. The Australian Cattle dog, the Belgian Malinois, and the American Pitbull have all appeared in separate places on the earth, over the past about 100 years, due to each having a low pressure; cuddled, environment that allowed each to differentiate. If these three dogs had appeared naturally, we would have attributed this to evolution. It shows what can happen if we selectively reduce the pressure. Humans merely speeded up the process with an exaggerated cuddle.

 

This is loosely analogous to time/temperature testing of plastics, where exaggerated parameters of temperature, allows us to predict, longer term properties, like 25 year plastics, in a few hours. Domestication did in 100 years what nature may take thousands, via concentrated cuddle time testing.

 

How is artificial selection low-pressure? You seem to be making the same mistake of conflating open niches (artificial in this case) with selection pressure. Breeding for particular traits seems like it's about as high-pressure as you can get.

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I've not read through every reply, but very simply. The amazon is not nessisarily easy to live in, a lot of creatures make lots of competition.

 

LOW PRESSURE results in more species (so greater biodiversity at a glance), and more individuals

 

HIGH PRESSURE results in faster evolution, but more deaths and more 'unusual' adaptions.

Now, just because it may only result in 'simple' organisms, doesn't mean it has less biodiversity then an enviroment with 'complex organisms'

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I think it goes back to a general misunderstanding of the concept of selective forces. The latter does not necessarily mean that an external force eliminates genotypes. Rather, selection occurs if certain genotype provide reproductive advantages. Even in a niche with virtually unlimited resources, certain sub-populations may be more effective in reproducing in this environment (e.g. they feed just a bit faster or have a higher reproductive cycle).

Also consider the opposite. Assume that there is one dominating, overbearing selective force that is the limiting factor of reproduction (say, the ability to forage and use a specific resource or escape predation). Under these circumstances any mutations affecting this specific trait negatively will be heavily selected against. I.e. negative traits vanish quickly but even small advantages would spread rapidly. OTOH, mutations not affecting it can still persist and even slightly negative traits may persist longer than in the absence of the given assumed selector (as the relative advantage would be higher).

 

If a new niche opens up or is explored, a whole host of other effects become more important, including non-selective forces (such as drift).

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Living in the Amazon is not easy for penguins or polar bears, or large mobile fauna generally.

 

It's probably kind of bleak for soil flora, underground life in general, as well.

 

Living beings reproduce exponentially - it doesn't take long for them to max out any given resource base, once enabled.

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My second hypothesis was too vague and wrong in too many different situations.

Hypothesis: More diversification of populations occurs in places and times when competitive pressure for resources is lower. The archaeological record supports this. More new species developed soon after major disasters than during the competitive times before the disasters. To extend the hypothesis: the same sort of effect can be seen with reductions in other types of survival pressures upon a species.

 

I still contend that most evolution occurs in places and times of plenty. However, my new basis for that contention is more of a spin on the definition of evolution. Places and times of plenty are defined as, situations in which a population is able to increase for two or more generations without immediately overburdening its habitat.

Evolution: Biology. change in the gene pool of a population from generation to generation by such processes as mutation, natural selection, and

genetic drift. --from Dictionary.com

 

The absolute number of genetically variant individuals within a population increases when a population increases and the rates of mutation and genetic drift remain steady. Therefore more changes occur in the gene pool of an increasing population than in a steady population.

 

This matters when variant individuals breed to produce more individuals with like variation. There are multiple mechanisms that can raise the odds of like individuals coming together to produce more variant offspring.


Migration for preference.

Others get killed off faster.

Increased density of the population.

Variants get expelled by normals.

Genetically dominant traits.

Inbreeding.


Has anybody seen evidence of migration for preference leading to the growth of a new subset of a species?

 

Congratulations to CharonY! -- You killed it for me.

SwansonT -- wounded it heavily.

 

Puppypower -- The selection of traits by an outside intelligence is indeed an accelerator of evolution. I am trying to figure out how evolution can happen quickly and even combine several traits that individually reduce the suitability for the original habitat.

 

As overtone mentioned, "Living beings reproduce exponentially." Because of this, the "overbearing selective force" as CharonY described (where weaker individuals get killed off faster) and the other mechanisms that concentrate individuals with like traits become more important. The odds are against a mating pair of individuals with the same mutation being born in the same place and time. Anything that increases the odds of them getting together to reproduce is significant. When they do get together, it can be like the start of a landslide. Boom! a new subspecies takes over.

 

I noticed that in the case of non-mobile species, the alternation of good times and bad times, I.E. weather variations, is what powers the evolution cycle. Expansion of a population into other territories, followed by concentration / isolation of individuals with certain traits.

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If you ever heard the saying, birds of a feather will stick together, this is about how groups select themselves. The ugly duckling is different from the group and will be driven out of the flock, so the group can maintain certain traits. Some of the selective pressure comes from consciousness and not just the environment.

 

In discussion forums, if the group says one thing and someone plays the role of the ugly duckling, who goes in another direction, a pressure will appear to maintain pure group blood; of the mind. Migration is often about the ugly duckling being pressured to leave, and therefore needing to find place where the pressure is less so it can start again and possibly form its own group, which will also seek pure blood. The story of the ugly duckling show he is actually a beautiful swan; of value.

 

Dogs are interesting in that the breeders will weed out the ugly ducklings, with some of the ugly duckling migrating (sold) and then becoming the foundation for other breeds, whose breeders then weed out the new ugly ducklings.

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If you ever heard the saying, birds of a feather will stick together, this is about how groups select themselves. The ugly duckling is different from the group and will be driven out of the flock, so the group can maintain certain traits. Some of the selective pressure comes from consciousness and not just the environment.

 

In discussion forums, if the group says one thing and someone plays the role of the ugly duckling, who goes in another direction, a pressure will appear to maintain pure group blood; of the mind. Migration is often about the ugly duckling being pressured to leave, and therefore needing to find place where the pressure is less so it can start again and possibly form its own group, which will also seek pure blood. The story of the ugly duckling show he is actually a beautiful swan; of value.

 

Dogs are interesting in that the breeders will weed out the ugly ducklings, with some of the ugly duckling migrating (sold) and then becoming the foundation for other breeds, whose breeders then weed out the new ugly ducklings.

 

This is one of the weirder interpretations of sexual selection mixed up with other effects that I have seen. I am not even sure how to address this.

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If you ever heard the saying, birds of a feather will stick together, this is about how groups select themselves. The ugly duckling is different from the group and will be driven out of the flock, so the group can maintain certain traits. Some of the selective pressure comes from consciousness and not just the environment.

 

Sexual selection favors rare traits in negative frequency dependent systems. http://www.indiana.edu/~curtweb/L567/readings/Sinervo%26Lively1996.pdf

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What are some of examples of these many mutations that survive only because of medicine?

 

 

 

Medicines for diabetes allow people to survive and live normal lives. Doctors will often ask if anyone in your extended family has or had diabetes since they know this can be passed forward. It will need medicine or else selective pressure can cause problems. The medicine reduces the stress and allows this genetic affect to pass forward. Now if someone has diabetes it is not even considered a big deal with respect to survival due to treatment options; lowered pressure.

 

 

 

But you are not the entire population; some people die from predation. As the joke goes, I don't have to run faster than the bear, I just have to run faster than you. So, not zero pressure.

 

Even with a low-pressure system present for a large fraction of the population, we have not split into multiple species. Humans are not the example you are looking for.

 

 

 

 

Lions and Tigers are considered separate species, yet they can mate and have cubs. These cubs are called Ligers. This mating does not happen in the wild due to geographical separation.

 

The point is science does not catalog humans in the same way as they catalog lions and tigers. This different set of catalog rules tends to funnel thinking down conceptually inconsistent lines in terms of evolution. One could say Australians and Canadians are separate species, like lions and tigers. It takes manmade means/choice for them to meet/mate to beget Custralians.

 

Different people from different races each have their characteristic physical features. These all come from common ancestors who migrated out of Africa. Migration is a wild card, since it is based on a conscience choice to move from high pressure to where there is less pressure and therefore more odds for selection. Migration allows the brain to pick an environment that best suits the strengths and weaknesses of the genetic clothes. It is not the DNA adapting to a fixed environment.

 

If humans had stayed in Africa, and therefore migration was not used to lower pressure for certain individuals, there would not be as many races of humans; separate species like lions and tigers who can mate.

Edited by puppypower

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Races are not separate species capable of intermating. Humans are not nearly that genetically diverse and "mixed race" offspring do not have fertility problems.

 

We're all the same species.

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In addition to the misunderstanding what races are (or not), the largest genetic diversity is found within Africa.

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Medicines for diabetes allow people to survive and live normal lives. Doctors will often ask if anyone in your extended family has or had diabetes since they know this can be passed forward. It will need medicine or else selective pressure can cause problems. The medicine reduces the stress and allows this genetic affect to pass forward. Now if someone has diabetes it is not even considered a big deal with respect to survival due to treatment options; lowered pressure.

So there was no diabetes survival before medication? It was never passed along?

 

Lions and Tigers are considered separate species, yet they can mate and have cubs. These cubs are called Ligers. This mating does not happen in the wild due to geographical separation.

 

The point is science does not catalog humans in the same way as they catalog lions and tigers. This different set of catalog rules tends to funnel thinking down conceptually inconsistent lines in terms of evolution. One could say Australians and Canadians are separate species, like lions and tigers. It takes manmade means/choice for them to meet/mate to beget Custralians.

The offspring of such mating (e.g. Ligers) are generally not fertile. That is not true of humans. One could say Australians and Canadians are separate species, but one would be spectacularly wrong.

 

 

Different people from different races each have their characteristic physical features. These all come from common ancestors who migrated out of Africa. Migration is a wild card, since it is based on a conscience choice to move from high pressure to where there is less pressure and therefore more odds for selection. Migration allows the brain to pick an environment that best suits the strengths and weaknesses of the genetic clothes. It is not the DNA adapting to a fixed environment.

 

If humans had stayed in Africa, and therefore migration was not used to lower pressure for certain individuals, there would not be as many races of humans; separate species like lions and tigers who can mate. One could say that

As I already noted, it's not just mating. Producing viable offspring is also a large factor.

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The point is science does not catalog humans in the same way as they catalog lions and tigers

Yes, it does.

 

The various races of lions, for example - there are heavy maned and light maned lions - are all lions.

 

 

Migration allows the brain to pick an environment that best suits the strengths and weaknesses of the genetic clothes.
I know of no examples of that. Do you know of any? Edited by overtone

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There is much talk of evolution occurring as a result of survival pressures. Yet the places where the greatest biodiversity can be found are the places where the living is easy, compare the Amazon to the Arctic. I contend that most evolution occurs in places and times of plenty. The basis for this contention is that during times of plenty, more of the in-between mutations survive to reproduce. This allows the more complex mutations and combinations of mutations to develop viable forms. These viable forms may gain significant survival advantages over the old forms. The new, more viable, forms then become the pressure that kills off the old forms.

One advantage to this view of evolution is that it does not require specific environmental factors to guide the selection of intermediate mutations. No purpose or goal is required, unlike the solutions from evolutionary computing.

 

I challenge everyone on this forum to contest my contention. It took me a few minutes (after years of reading for curiosity) to come up with this. How long will it take you to accept it?

 

Hypothesis: More mutations will be found, living, among populations during good times than during lean times. This requires controlling for lean times that occur from circumstances that do not specifically cause mutations.

 

Hypothesis: More diversification of populations occurs in places and times when competitive pressure for resources is lower. The archaeological record supports this. More new species developed soon after major disasters than during the competitive times before the disasters. To extend the hypothesis: the same sort of effect can be seen with reductions in other types of survival pressures upon a species.

 

P.S. Remember, "You are doing the job right only when you are having fun in the process!"

More resources means higher carrying capacity means more individuals means more mutations to select from means faster evolution. Tada! Your hypothesis is unnecessary.

 

edit

Maybe that's overly simplistic. I was thinking genetic variability. If biodiversity is the number of species, however, then we must consider the formation of barriers to reproduction, which are what cause speciation.

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There is much talk of evolution occurring as a result of survival pressures. Yet the places where the greatest biodiversity can be found are the places where the living is easy, compare the Amazon to the Arctic. I contend that most evolution occurs in places and times of plenty.

 

Hypothesis: More diversification of populations occurs in places and times when competitive pressure for resources is lower.

 

It seems that you are assuming that the pressure to survive is lower in places where there is abundant resouces, i.e. water, sunlight, temperature.

 

Even in a rich and highly diverse environment such as a rainforest the pressure to survive is enormous, yet it doesn't arise due to a lack of resources. The pressure comes from predation and competition for those resources.

 

Predation pressures favor those individuals with characteristics which give them an advantage in avoiding predation, for example, camouflage or poisonous skin in a frog, or toxins in a plants leaves or fruit.

 

Competition pressures favor those individuals with characteristics which give them an advantage in obtaining resources in a highly competive environment. For example, the camouflage in a snake to help it catch prey, or the ability to tolerate plant toxins in an insect or herbivore.

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It seems that you are assuming that the pressure to survive is lower in places where there is abundant resouces, i.e. water, sunlight, temperature.

 

Even in a rich and highly diverse environment such as a rainforest the pressure to survive is enormous, yet it doesn't arise due to a lack of resources. The pressure comes from predation and competition for those resources.

 

Predation pressures favor those individuals with characteristics which give them an advantage in avoiding predation, for example, camouflage or poisonous skin in a frog, or toxins in a plants leaves or fruit.

 

Competition pressures favor those individuals with characteristics which give them an advantage in obtaining resources in a highly competive environment. For example, the camouflage in a snake to help it catch prey, or the ability to tolerate plant toxins in an insect or herbivore.

 

Conversely where resources are poor or environmental conditions extreme, the factors driving selection are very strong with narrow bounds; temperature, pH, water, etc extremes.

 

It's important to remember that selection *reduces* variability and so it is perhaps not surprising that in very strongly selective environments you find only a few survivors.

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Going back to the apple maggot flies, there would have been, in the original population, some flies which found both hawthorns and apples to be acceptable places to lay eggs. Others would find only hawthorns acceptable. Those which found hawthorns unacceptable did not lay eggs. Then a new option appeared and some flies which would not lay eggs on hawthorns had an acceptable place to lay their eggs. The selection pressure against these specific flies disappeared and they became numerous enough to "suddenly" appear.

 

If there had been maggot flies that found both apples and hawthorns suitable then the species would not likely have sorted out into two separate species without some reason to select for separate breeding. I'm not up on the species and not sure which came first but let's say the apple maggot fly population existed first. Mutations that encoded for hawthorn preference would have to be recessive or in some other way not acted upon or the first individual to be born this way would have found no mates on the hawthorns with which to breed. Recessive genes can continue within a population quite well. When individuals are born with twice the recessive genes for hawthorn predation they will go look for hawthorns on which to feed and breed. Over generations the individuals with two copies of the hawthorn predation gene will occur frequently in batches if for no other reason than they were all born to the same parents each of whom must have carried the hawthorn predation gene. Considering how many offspring one pair of insects can produce in a season, there could be quite a large number of such offspring. Inevitably some of these individuals will encounter each other and having no better options will mate with each other. All of their offspring would then have the two copies of the hawthorn predation gene. Other genes they carry would stand a good chance of also being present in two copies each. In one generation the population would have a high level of homozygosity on many characteristics. Subsequent generations would produce more heterozygosity as more individuals are born from the original apple population.

 

After a while the hawthorn population will develop new traits that are more useful on hawthorns than they might be on apples. As new individuals from the original apple population continue to bring in apple-effective genes, the hawthorn population will need to develop breeding selection methods to thwart this or their offspring will not improve their reproductive success. If the population succeeds in finding a mating preference that prevents these invaders in their gene pool from reproducing successfully, the population will then evolve away from the apple type and restrict the options for any new apple-born hawthorn eaters putting a pressure on those new incomers which either starve from completion and lack of reproductive partners. If the hawthorn maggot flies do not produce a means of reproductive isolation then they will continue to be apple maggot flies feeding on hawthorns and not biologically or even genetically diverse from their parent population and probably not as reproductively successful either. Selection pressure does push for biological diversity in close quarters when it does happen. But most evolution is caused by new locations. Hawthorn trees are not the same "place" as apple trees for animals as small as flies. There is also a limit to the numbers of apple flies that can survive on one apple tree. Apple trees produce toxins to reduce infestations. There are also predators of apple flies (one presumes) and so there are stresses on the apple flies that encourage the reproduction of some specimens as it discourage it in others.

 

The hawthorns would have presented new stresses for the hawthorn eating flies. Sure there might have been plenty to eat but it might not have been as good for them as apple trees would have been. If the population can prevent or reduce the influx of new DNA from the apple population they would have a chance to adapt to the new environment by the accumulation of mew mutations some of which might be more useful on hawthorns. With possibly fewer predators and less competition early on, they would be able to accumulate quite a bit of genetic diversity much of which would likely be hidden or very slight in function. Flies breed fast and produce lots of offspring making this an almost certainty. Stressors like the environment itself (despite all that food) and competition from all of those other hawthorn eating flies will produce the changes that we call biological diversity. Biological diversity is not the same thing as genetic diversity. Biological diversity is produced from the genes and the environment jointly. Genetic diversity is not dependent on the environment particularly for the most part.

 

This is one of the weirder interpretations of sexual selection mixed up with other effects that I have seen. I am not even sure how to address this.

 

I think puppyppower might be referring to assortative mating strategies.

 

Assortative mating
Assortative mating is a mating pattern and a form of sexual selection in which individuals with similar genotypes and/or phenotypes mate with one another more frequently than would be expected under a random mating pattern. Examples of similar phenotypes include, but are not limited to, body size, skin coloration/ pigmentation, and age.

​Some species do select individuals that look more like themselves. This is more common in birds and may be due to imprinting on their parents and other flock members. Not all sexual selection would work this way though as bird's of paradise have wildly differing appearances and yet females do not know what their fathers or other males looked like particularly. They still usually pick the right males by appearance which is likely genetically hardwired.

 

(Hybrids are common between the various species and even genera. Males know what females look like but the females of most of these species look a lot alike. That and males tend to be less fussy anyway. Some females may possess recessive genes or new mutations coding for a new or old preference.)

 

Mammals usually use their sense of smell, preferring to mate with individuals with a similar smell to what they grew up with.

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More variants survive whilst the opportunities are there, presumably before every niche gets filled after which things aren't so 'easy'. There is never an absence of competition but being diminished means the increasing variation part of evolution gets a boost. When the niches are filled and competition is more pervasive, the natural selection, decreasing variation part of evolution comes more into play.

 

Humans seem to be have be in a 'finding and exploiting new opportunities' and 'more variants surviving' phase and with global transport there aren't truly geographically/genetically isolated sub populations to achieve speciation. How close we are to overfilling our niches and facing a backlog of natural selection is a question, but humans are socially, technologically and otherwise variable in crucial but non-genetic ways, ways that can evolve at rates unconstrained by genetics and will likely continue to be so exceptional that normal rules of evolution won't apply.

Edited by Ken Fabian

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