Evolution of Animal Adaptations: Polar Bears

[bassplayer142]

It's simple to understand that when an animal lives in a certain enviorment it begins to adapt to it. An animal changes colors over time or develops different body protection like hair or fur. Take a Polar bear for a good example. Since they live in a very very cold region they evolved into having fur. The fur itself actually is hollow with air trapped inside. Now air is a bad insulator in general but when it is in a small area where it doesn't move well it is a very good insulator. My question is, is how does evolution "know" these things. I understand how fur could evolve but how could these hollow fur tubes be known by nature.

 

[ganstaman]

If you really understand how fur could evolve, than you already understand the answer.

It's the same principle all the time: some mutation occurs leading to an individual with a different phenotype. If this phenotype makes the individual more likely to procreate, then that genotype will become more prevalent.

So nature doesn't 'know' that fur keeps you warm or that hollow fur tubes work better. But it seems that having fur lead to more mating and having hollow fur tubes lead to even more mating.

 

[jim mcnamara]

Evolution knows nothing. It has no direction or knowledge about anything. Natural Selection drives which random mutations in the genetics of a population are left to be passed on to the next generation. If a change in genetics favors one individual, that individual is more successful at reproduction. Over many generations the traits that confer success become more common.

 

[ganstaman]

Ah, reproduction was the word I wanted to use but somehow couldn't remember at the moment of my post. Not that it really matters anyway...

 

[Chilodonella]

On a side note to these answers, I recently attended a seminar from a Bio-Physicist at Rice University doing work on a single celled eucaryotic organism. He was presenting results from a series of experiments his lab had done. Briefly, a environment was created where all variables, (ie. temp, humidity, growth medium) where all controllable. The device looked like a small metallic container with a bunch of hosing and wiring going into the machine. The purpose was to place a population of these quickly reproducing organisms into the device, then over a period of 30 days raise the temperature to a range outside of optimal from the populations growing setting. At set intervals his team took a sample out of the device and sequenced it for a highly conserved and essential coding region. The results showed a mutation always occurred to that gene that allowed it to survive better as the temp rose, then that mutation would die off, and another different mutation would become more favored and prosper. Basicly there was a series of mutations that would occur allowing the offspring of that original group to live and adapt (ie. more fit and reproduced more). Now the point relating it to your question is, that every time the experiment was run, the exact series of mutations occurred at the exact same time. No matter how many times he ran the experiment the evolution followed the exact same path. So does evolution "know" how best to evolve? Form always fits function, so can you claim that evolution "knows" what it is doing? I kinda think that there might have been polar bears with non-hollow fur, they just didnt stay as warm as the one with hollow.

 

[Moonbear]

The key point to recognize is that a particular variant of a trait needs to already exist in the population before the change occurs. The majority of individuals may not have that trait, so a random sampling, such as Chilodonella described, would be more likely to miss that variant among all the other individuals without it. And, of course that variant needs to NOT be detrimental prior to the change in climate, habitat, etc., so that it continues to exist among enough individuals even if just in a very low percentage of the population. When the conditions change, the individuals without that trait simply die off because they are unfit, and those with the variant trait become the predominant proportion of that population because they can survive that change.

So, just to reiterate, in evolution, a trait must exist BEFORE the environmental change, it is not acquired after the environmental change or in response to the environmental change. Instead, those "lucky" individuals that had it before the environmental change will be the remaining survivors when everyone else dies off because they don't have the right traits.

As an example, just look at the variations in humans for a trait such as body hair in men (harder to tell in women because they go to great lengths to remove most of it). You'll notice that there are men who have almost no body hair or facial hair, or it's very fine, and at the other end of the spectrum, there are those covered from head to toe in thick mats of body hair. Humans are able to modify our environment to suit our own needs, so we see all these variants thriving equally well among our population, and there's no particular advantage or disadvantage to having more or less body hair (other than perhaps a bit of "eww" factor regarding very hairy backs at the beach). But, should we become more vulnerable to the outside environment without the protection of heating and air-conditioning, we may see that shifts in temperature up or down would alter the survival rates of men with or without hair, making one more favored than the other in the population. I'll note that this isn't an ideal example, because that body hair doesn't develop until puberty, so children still need to be able to survive to adulthood without the hair, and could father a child before succumbing to the deleterious effects of their body hair if such a selection happened, but it's just a fairly accessible example of a trait where you can easily observe a wide range of variation in the natural population without having to think of someone as a "mutant."

 

[Chilodonella]

Yes I agree that evolution "before" a bottle necking event is most likely always the case. I would argue it is very hard to test that though. The study i am talking about used a fresh sample of population organisms everytime, and everytime the same sequence of mutations occurred over the 30 month test. For example, a phenotype would be most populus through a certain temp range (most fit), then die and another phenotype would take its place, so on and so forth. The amazing thing is that the same pattern emerged each time.

With out the presence of a bottle necking event, the force that pushes evolution is just random mutations within a population. As something causes a stress on the population only the "fittest" phenotype will survive. But, natural selection I would argue is less of a factor in the overall picture of evolution than the random mutations over time.

 

[GleefulNihilism]

With all due respect to the people that beat me to the technical answers.

Short Version: It doesn't, and there's lots of dead bears that will attest to that.

 

[Luidge]

I recently came across good articles on evolution. It may or may not be exactly what the original poster was looking for, but I think it's worth a read

http://www.sciam.com/article.cfm?id=human-evolution-appears-t
http://www.sciam.com/article.cfm?id=are-human-beings-still-ev
http://www.sciam.com/article.cfm?id=experts-random-mutations

 

[Chilodonella]

The last paper answers the question exactly.

 

[Cheer 28339]

Inbreeding: Take the white tiger. One was found, and he was bred with plain ones in hopes to create more white tigers (because people like how they look). Then, White tigers were bred with their siblings. That resulted in effects crossed-eyed tigers, due to inbreeding.

Natural Selection will either kill off or spare a mutated animal, depending on if the mutation is beneficial or not. According to Charles Darwin, the mutation will become hereditary. Would that mean that, say, polar bears are all related? Why would they not be mutated due to inbreeding?

 

[BoomBoom]

Inbreeding: According to Charles Darwin, the mutation will become hereditary. Would that mean that, say, polar bears are all related? Why would they not be mutated due to inbreeding?

Darwin would not have the slightest clue as to what you meant by "mutation". He believed the driving force of evolution was purely random variation...he was wrong.

The reason that inbreeding can be bad is that it brings out recessive genes. If some of these are harmful it can be bad, but if they are helpful it can be good. The majority of evolutionary "leaps and bounds" have occurred in isolated populations where inbreeding was commonplace.

While DNA mutations are random, I believe there are mechanisms in place within the genome under stress conditions which allow mutations to occur at a more rapid rate for certain regions of the genome.

 

[russ_watters]

My question is, is how does evolution "know" these things. I understand how fur could evolve but how could these hollow fur tubes be known by nature.

How does water know how to flow downhill?

Evolution is basically a force of nature, just like gravity making a river flow. They even use some of the same terms, like pressure. In this case, the pressures are mating and death. Ie, if a bear doesn't have enough fur and it is cold, it may die while bears with more fur live.

 

[moe darklight]

Inbreeding: Take the white tiger. One was found, and he was bred with plain ones in hopes to create more white tigers (because people like how they look). Then, White tigers were bred with their siblings. That resulted in effects crossed-eyed tigers, due to inbreeding.

Natural Selection will either kill off or spare a mutated animal, depending on if the mutation is beneficial or not. According to Charles Darwin, the mutation will become hereditary. Would that mean that, say, polar bears are all related? Why would they not be mutated due to inbreeding?

well, yes and no. In a sense we are all related and mutated (isn't that poetic? ... maybe in a marvel comics sort of way): we all evolved from the same organisms.

what you have to keep in mind though, is that all of this takes thousands and thousands of years, very slowly.

the problem with selective inbreeding like that is that it's not a natural path of evolution: it's done rashly over a very short period of time, and using a very small population of animals that are related to each other. that means that there is very little variety... which is how these side effects of inbreeding arise (there is a higher chance of a defective trait to be present in the animals that are reproducing and passed on).

that kind of thing is not likely to happen in nature because a tiger that carries the cross-eyed trait would not be very likely to live long enough to reproduce.

How does water know how to flow downhill?

nice

 

[_Mayday_]

To the threadstarter, I would advise reading abit more into evolution, evolution doesn't know anything, and covering it all in one post would not do it justice. Have a look around the web is an excellent resource.

 

[Cheer 28339]

My question is, is how does evolution "know" these things. I understand how fur could evolve but how could these hollow fur tubes be known by nature.

I read that some flowers have changed to attract insects by changing shape/color. Although plants are considered "alive", it does not have a brain to think:

I need to pollinate, so if I turn red and lose some petals here, the bugs will come.​

How can these plants change, then?

 

[BoomBoom]

I read that some flowers have changed to attract insects by changing shape/color. Although plants are considered "alive", it does not have a brain to think:

I need to pollinate, so if I turn red and lose some petals here, the bugs will come.​

How can these plants change, then?

Do you "think" about which of you genes are expressing themselves and at what rate, or what mutations occur within your genome?

"Thinking" is not necessary in the slightest for evolution to occur. Living things just naturally adapt and "fine tune" themselves to the envoronment in which they live. In the example you list, through random variation, if the bugs like a certain type of flower over the others, then they will preferentially pollinate the plants thet they like the most. So in that specific example, it is the bugs that are in control of how the plants evolve.