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Author Topic:   How do we know about natural selection? (Igor and Lithodid-Man only)
Lithodid-Man
Member (Idle past 486 days)
Posts: 504
From: Juneau, Alaska, USA
Joined: 03-22-2004


Message 16 of 43 (299362)
03-29-2006 1:41 PM
Reply to: Message 15 by igor_the_hero
03-27-2006 5:04 PM


Re: Great question!
Hi,
Sorry for the delay in response but this week is full. I will write a short bit here then hopefully more later.

Ok, I understand you. I think. But how would you prove it?

This is one of the points in science that most people (even some scientists!) find confusing. Science never 'proves' anything. Are you familiar with the Sherlock Holmes axiom "It is an old maxim of mine that when you have excluded the impossible, whatever remains, however improbable, must be the truth" ? This is close to how science operates.

Let's say that you have published your paper on dandelions, strongly suggesting that your #3 is supported (remember, we 'excluded the impossible' by disproving #1 & 2). Years later, another researcher makes a new discovery that ant poison can make plants stunted in growth. After reading this you realize that you did not eliminate all other possible answers, there is a #4 hypothesis you didn't think of because the principle was unknown when you published. If you believe that it is another possible solution you might redo your experiments but add another, one that would disprove #4 if it were impossible.

This is how science works (in part, I haven't discussed the predictability aspect yet). This is also why new discoveries in all of the sciences can lead to a flurry of activity as scientists check their findings against the new findings.

What we use instead of proof in science is this idea of predictability. Your dandelion paper was about one particular lawn you studied. But your principle should apply to all dandelions in a ll lawns. In essence you are saying, "If hypothese 3 is correct I predict that dandelions in any mowed lawn will be shorter than their cousins in unmowed habitat".

The very next day another researcher could look at his well-mowed lawn with tall dandelions and say, "Nope, not in my lawn". This doesn't disprove your hypothesis (doesn't strengthen it either neccessarily) as there could be a number of factors involved. Maybe his mower doesn't a have a bag so the tall seeds are scattered back onto the lawn while yours are hauled away to the dump and so on. You would then devise ways to test more hypotheses.

The important this to remember though is even if 100 researchers examine 1000 lawns and everyone of them conforms to your prediction, you still haven't proven anything. Your work is very strongly supported. You might say with 99.9% confidence that the next lawn (number 1001) will also have short dandelions. Again if it doesn't you don't toss out your whole idea, you search for reasons behind the exception.

Also, when you are selecting, you have to have a selector, correct?

Well yes and no. There has to be something selecting but that doesn't have to be intelligent. In the case of a dog breeder the selector is the breeder. In the case of the dandelions the selector is the mower. But again picture a population of deer that live on a mountain slope. Those with thin coats do no not survive the winter as frequently as those with thick coats. In this case it is only the climate that is the selector. So basically, from a biological standpoint, your 'selector' is just the environment and environmental factors.
The dog-breeder is consciously selecting what they want in the next generation. The lawn mower or the climate are not choosing intelligently what traits will be in the next generation but the effect is the same (some will survive, some will not).


This message is a reply to:
 Message 15 by igor_the_hero, posted 03-27-2006 5:04 PM igor_the_hero has responded

Replies to this message:
 Message 17 by igor_the_hero, posted 03-30-2006 4:03 PM Lithodid-Man has responded

    
igor_the_hero
Inactive Member


Message 17 of 43 (299621)
03-30-2006 4:03 PM
Reply to: Message 16 by Lithodid-Man
03-29-2006 1:41 PM


Re: Great question!
But in your example about the deer, you couldn't really consider the environment. A lot of animals migrate so that they can survive.
This message is a reply to:
 Message 16 by Lithodid-Man, posted 03-29-2006 1:41 PM Lithodid-Man has responded

Replies to this message:
 Message 18 by Lithodid-Man, posted 03-31-2006 5:07 AM igor_the_hero has responded

  
Lithodid-Man
Member (Idle past 486 days)
Posts: 504
From: Juneau, Alaska, USA
Joined: 03-22-2004


Message 18 of 43 (299737)
03-31-2006 5:07 AM
Reply to: Message 17 by igor_the_hero
03-30-2006 4:03 PM


Re: Great question!
But in your example about the deer, you couldn't really consider the environment. A lot of animals migrate so that they can survive.

Great point! Think about this, there may be many possible solutions to an environmental condition. Heavier fur, a tendency to migrate, an ability to hibernate, all off these are possible solutions to a changing cold environment. Depending on the species each may preferred.

For a species such as a deer migration may be the best solution. Picture a population of deer in a relatively protected valley (winters are fairly mild, lots of food, etc). If there is a series of colder winters over several years the protected valley becomes a harsher place, at least during winter months. Those individuals who by habit wandered towards better forage during the winter (even when it was 'nice' still in the valley) would surivive better and have more offspring. As the climate changed and winters in the valley became harder, they already had the tendency to seek better forage and would therefore do better. Every spring when these 'wanderers' came back to the rich valley they might find fewer and fewer of their group alive, or, even if alive, not as healthy and able to produce offspring. In a short time bucks would find themselves competing for mates with starved, scraggly competitors. It doesn't take many generations until we would see that all of the deer in this population are migrating out of the valley during the winter and returning when it is spring. The trait for migration has been selected!

Here is another scenario with the same deer. Let's say that the valley they live in is actually the best around. Even when the climate has changed over years there is nothing better nearby, in fact the forage is worse during the winters then the crappy forage they have in the valley. In this population the wanderer's do even worse than the one who stay behind and deal with it. They might only last a few winters before the wander gene is extinct. But of those that wait out the winter the ones who have traits that allow them to do better may survive. This could be thicker fur. This could be those that had a tendency to over-eat during the fall and had thicker fat. Maybe both of those types would do better and have more offspring. We might expect to see this population tending towards those individuals that BOTH stored fat and grew a winter coat (the two types would both survive, both reproduce, within the same population).

I live on Baranof Island in Alaska. Here our native deer are called Sitka Black Tail. In reality they are mule deer. I don't know your familiarity with deer, but mule deer are huge. Generally over 200 pounds for bucks (and up to 300 pounds or more). Our Sitka Black Tail (I am in Sitka) GET TO 120 pounds and are usually 80 - 100 pounds for bucks. They are tiny deer. The first time I saw a hunter carrying one out of the woods I thought it was terrible they shoot fawns here. As it turns out the reason they are so small is they are forest deer. Our winters are fairly mild, and open grassland simply doesn't exist (we have peat bogs instead of grassland or fields). These deer live and forage in thick brush during the fall, summer, and spring. Better to be small. During the winter they scrape and forage in the old growth or on the beach. Again better to be small. Small but soooo delicious.

Anyway, I hope this makes sense. Deer and dandelions are just examples. If you want to blow your mind think that there are over 10 million species on this planet, and each of them have an environment that changes. For each of those there are different potential adaptations, different solutions. Only some of the offspring of those millions will survive. Some will find one way to live, others another, others will become extinct. Something to ponder....


This message is a reply to:
 Message 17 by igor_the_hero, posted 03-30-2006 4:03 PM igor_the_hero has responded

Replies to this message:
 Message 19 by igor_the_hero, posted 04-01-2006 12:47 AM Lithodid-Man has responded

    
igor_the_hero
Inactive Member


Message 19 of 43 (299975)
04-01-2006 12:47 AM
Reply to: Message 18 by Lithodid-Man
03-31-2006 5:07 AM


Re: Great question!
What if you get a perfect species suited to one particular spot? Like your deer in the valley. Now, let's say you have some sort of natural disaster that throws it all out of wack. Then your deer go extinct because the aren't adapted to the changes that take place in the disaster. Would that be considered natural selection?
This message is a reply to:
 Message 18 by Lithodid-Man, posted 03-31-2006 5:07 AM Lithodid-Man has responded

Replies to this message:
 Message 20 by Lithodid-Man, posted 04-01-2006 1:37 AM igor_the_hero has responded

  
Lithodid-Man
Member (Idle past 486 days)
Posts: 504
From: Juneau, Alaska, USA
Joined: 03-22-2004


Message 20 of 43 (299986)
04-01-2006 1:37 AM
Reply to: Message 19 by igor_the_hero
04-01-2006 12:47 AM


Re: Great question!
Then your deer go extinct because the aren't adapted to the changes that take place in the disaster. Would that be considered natural selection?

Yes, it would. But in this case selection occured without evolution. Sometimes there are no survivors, no 'winners'. Evolution (change) can only occur when the selection process leaves survivors that may pass on the trait the helped them survive. Also, there are some disasters that take out the fit and the unfit. In the deer example it could be a fire. No mutation, no adaption in deer makes them fireproof. Keep up the good questions!


This message is a reply to:
 Message 19 by igor_the_hero, posted 04-01-2006 12:47 AM igor_the_hero has responded

Replies to this message:
 Message 21 by igor_the_hero, posted 04-01-2006 8:57 AM Lithodid-Man has responded

    
igor_the_hero
Inactive Member


Message 21 of 43 (300011)
04-01-2006 8:57 AM
Reply to: Message 20 by Lithodid-Man
04-01-2006 1:37 AM


Re: Great question!
Does natural selection ever have any unexplained changes? I mean like the chaemeleon. There are plenty of animals out there that are camoflauged without having to change colors. What could happen that would make it so that the chaemeleon would need that ability to change how it does?
This message is a reply to:
 Message 20 by Lithodid-Man, posted 04-01-2006 1:37 AM Lithodid-Man has responded

Replies to this message:
 Message 22 by Lithodid-Man, posted 04-03-2006 2:07 AM igor_the_hero has responded

  
Lithodid-Man
Member (Idle past 486 days)
Posts: 504
From: Juneau, Alaska, USA
Joined: 03-22-2004


Message 22 of 43 (300469)
04-03-2006 2:07 AM
Reply to: Message 21 by igor_the_hero
04-01-2006 8:57 AM


Re: Great question!
Does natural selection ever have any unexplained changes?

I think I understand (based on your next question) what you are saying. But your question is incorrectly worded. You might think of it in terms of "Can natural selection account for adaptation for a trait that might be solved by a simpler adaptation?" If that is confusing I hope I can explain using your example.

I mean like the chaemeleon. There are plenty of animals out there that are camoflauged without having to change colors.

I am going to start by telling you that I am not a squamatiid (lizards and snakes) expert, my area is in invertebrates. But I know a bit and have some references on hand. As I understand it lizards are split into two groups, Iguania (Iguanas, Old World Iguanas, and Chameleons) and Scleroglossa (all other lizards and snakes).

One of the traits found throughout the Iguanids is the ability to pump melanin (dark pigment) within their cells of the third skin cell layer. The second cell layer is yellow, the first is blue. So in most iguanids the default (no change) color is green (blue top layer + yellow under layer). By pumping melanin (black) towards the surface they are able to change skin color from green to nearly black. Red is produced by capillaries (blood) near the skin surface.

How this evolved? Mystery to me. Because as a group their default color is green, it might make sense that individuals who had the ability to hide their greeness in conditions with a different background color might have prevailed. Those green individuals with more melanin in the third skin layer might have survived better that those that were green, changing to a brown skin color. Later it might be that those individuals with the ability to simply change from green to brown did better than those that were only brown. From there who knows? I will look around and see if I can find any tested hypotheses on the development of color changing ability in reptiles. I do know that a number of these lizards, including chameleons, use skin color and pattern to attract mates and frighten off rivals.

The important point is that we have multiple tools in science for answering these questions. Physiologists can examine the cells and tell us HOW the color change works. Geneticists and taxonomists (those that classify organisms) can look at lizards and tell us which are closely related and which are not. Behavioral ecologists can look at how color change is used. Together we can construct a plausible outline for how the ability came to exist in its amazing modern form.


This message is a reply to:
 Message 21 by igor_the_hero, posted 04-01-2006 8:57 AM igor_the_hero has responded

Replies to this message:
 Message 23 by igor_the_hero, posted 04-03-2006 4:22 PM Lithodid-Man has responded

    
igor_the_hero
Inactive Member


Message 23 of 43 (300669)
04-03-2006 4:22 PM
Reply to: Message 22 by Lithodid-Man
04-03-2006 2:07 AM


Re: Great question!
Ok. It still confuses me some but I think I understand. Now can you tell me why there are tons of animals out there dying from rainforests being cut down (which you have said is a form of natural selection) and are not doing anything that is helping them to stay alive? If natural selection inspires a change than shouldn't there be species of the same animal popping up all over with new characteristics?
This message is a reply to:
 Message 22 by Lithodid-Man, posted 04-03-2006 2:07 AM Lithodid-Man has responded

Replies to this message:
 Message 24 by Lithodid-Man, posted 04-05-2006 3:58 PM igor_the_hero has responded

  
Lithodid-Man
Member (Idle past 486 days)
Posts: 504
From: Juneau, Alaska, USA
Joined: 03-22-2004


Message 24 of 43 (301232)
04-05-2006 3:58 PM
Reply to: Message 23 by igor_the_hero
04-03-2006 4:22 PM


Re: Great question!
Hi Igor,

Clearing a rainforest is not itself natural selection but an environmental change that may allow selection to occur. Remember, selection is a)differences in organisms and b)those differences allow some types to do better than others. One common cause of selection is environmental change and this can be rainforest destruction.

What is unique about our destruction of the forests is the speed and scale. If the forests were shrinking in size due to long-term climate change (as has happened before) then many species would be able to adapt. Few species can adapt sufficiently to survive massive change within a decade or less. Selection can only operate on those traits that appear in the population. For rainforest animals they have to not only face a lack of trees but other species that are already adapted to open areas. It is possible, even probable, that some rainforest forms will adapt. But most will either die or keep retreating with the forest. I remember in Central America seeing parrots begging french fries from a McDonalds. It is possible that those individuals who learned to do this might do better than their fruit-eating relatives who are sticking to the jungle. There are bird species like the rock pigeon (our common pigeon) and the English sparrow that are no longer found 'in the wild' but are exclusively associated with human habitation.

If there are points from my past comments you have questions about, please feel free to do so. As I mentioned before, you ask good questions and that is a really big step in understanding. Take care -LM


This message is a reply to:
 Message 23 by igor_the_hero, posted 04-03-2006 4:22 PM igor_the_hero has responded

Replies to this message:
 Message 25 by igor_the_hero, posted 04-05-2006 4:41 PM Lithodid-Man has responded

    
igor_the_hero
Inactive Member


Message 25 of 43 (301262)
04-05-2006 4:41 PM
Reply to: Message 24 by Lithodid-Man
04-05-2006 3:58 PM


Re: Great question!
Is it possible to get natural selection and no change? I mean you have an animal that is poorly suited to its environment. Then a catastrophe changes its habitat to make it perfectly suited to a new one.
This message is a reply to:
 Message 24 by Lithodid-Man, posted 04-05-2006 3:58 PM Lithodid-Man has responded

Replies to this message:
 Message 26 by Brad McFall, posted 04-05-2006 4:44 PM igor_the_hero has not yet responded
 Message 28 by Lithodid-Man, posted 04-06-2006 8:48 PM igor_the_hero has responded

  
Brad McFall
Member (Idle past 2588 days)
Posts: 3428
From: Ithaca,NY, USA
Joined: 12-20-2001


Message 26 of 43 (301266)
04-05-2006 4:44 PM
Reply to: Message 25 by igor_the_hero
04-05-2006 4:41 PM


two catastrophes

If the wind blows the species to a different environment and THEN the catastrophe occurs, I suppose so. I bet a little googling could demonstrate the existence of such proclaimed.

This message has been edited by AdminJar, 04-05-2006 03:46 PM


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AdminJar
Inactive Member


Message 27 of 43 (301267)
04-05-2006 4:45 PM
Reply to: Message 26 by Brad McFall
04-05-2006 4:44 PM


Brad, this is a Great Debate
I need to hide your post.
This message is a reply to:
 Message 26 by Brad McFall, posted 04-05-2006 4:44 PM Brad McFall has not yet responded

  
Lithodid-Man
Member (Idle past 486 days)
Posts: 504
From: Juneau, Alaska, USA
Joined: 03-22-2004


Message 28 of 43 (301771)
04-06-2006 8:48 PM
Reply to: Message 25 by igor_the_hero
04-05-2006 4:41 PM


Re: Great question!
Is it possible to get natural selection and no change? I mean you have an animal that is poorly suited to its environment. Then a catastrophe changes its habitat to make it perfectly suited to a new one.

Before I start it is important to keep in mind that 'perfectly suited' probably doesn't exist. Very well suited does, but there is always room for improvement.

There are in nature what we refer to as 'pre-adaptations'. These aren't organisms that are poorly adapted to a particular environment. But they have a trait that allows them to exploit a new environment (or a changed one) immediately, with little change to themselves. One example that comes to mind is that of the rock pigeon (the common pigeon). They traditionally nest in holes on cliff faces, a relatively uncommon (at least overall) habitat. But this habit made them able to move right into human cities as we create lots of vertical faces with holes. Now this species is found world-wide and in vast numbers. The ancestors were pre-adapted to raising young in a particular habitat, one that was patchy in distribution. Then along comes a species that not only wastes a lot of food but also creates this habitat en masse.

I am trying to think of other examples, I will keep thinking about it. Take care- Aaron


This message is a reply to:
 Message 25 by igor_the_hero, posted 04-05-2006 4:41 PM igor_the_hero has responded

Replies to this message:
 Message 29 by igor_the_hero, posted 04-06-2006 8:57 PM Lithodid-Man has responded

    
igor_the_hero
Inactive Member


Message 29 of 43 (301775)
04-06-2006 8:57 PM
Reply to: Message 28 by Lithodid-Man
04-06-2006 8:48 PM


Re: Great question!
What if you get natural selection and no mutation? If you have to wait billions of years for a helpful mutation, wouldn't natural selection cause the species to go extinct?
This message is a reply to:
 Message 28 by Lithodid-Man, posted 04-06-2006 8:48 PM Lithodid-Man has responded

Replies to this message:
 Message 30 by Lithodid-Man, posted 04-07-2006 3:06 AM igor_the_hero has responded

  
Lithodid-Man
Member (Idle past 486 days)
Posts: 504
From: Juneau, Alaska, USA
Joined: 03-22-2004


Message 30 of 43 (301817)
04-07-2006 3:06 AM
Reply to: Message 29 by igor_the_hero
04-06-2006 8:57 PM


Waiting for mutation

What if you get natural selection and no mutation? If you have to wait billions of years for a helpful mutation, wouldn't natural selection cause the species to go extinct?

Bingo! You have hit on a critical point in evolution. Because natural selection operates on mutations, changes have to coincide with the selection event. This is why slow changing environments favor species adapting and changing while environments that change very quickly are likely to lose most if not all of their species.

One important point, however, it doesn't take billions of years for helpful mutations to occur. Most mutations are neutral (and neutral mutations may be beneficial or harmful in the new environment). Every living being on the planet has some mutations (every human has at least several!). The vast majority of these mutations will never be observed and will simply persist in the background or go extinct over generations. But sometimes a slight (or even great) advantage will be conferred. When the presence of one of these coincides with environmental change, we might then see that trait undergo further selection in future generations. Eventually the descendents are very different from their original type.


This message is a reply to:
 Message 29 by igor_the_hero, posted 04-06-2006 8:57 PM igor_the_hero has responded

Replies to this message:
 Message 31 by igor_the_hero, posted 04-09-2006 10:02 PM Lithodid-Man has responded

    
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