Author Topic: Island lizards evolve..  (Read 1236 times)  Share 

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Offline Tero

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Island lizards evolve..
« on: September 27, 2013, 02:29:59 PM »

Offline Jstwebbrowsing

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Re: Island lizards evolve..
« Reply #1 on: September 27, 2013, 05:21:35 PM »
That sounds a lot like adaptation which I thought was incorrect?
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Offline Gilgamesh

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Re: Island lizards evolve..
« Reply #2 on: September 27, 2013, 06:04:49 PM »
That sounds a lot like adaptation which I thought was incorrect?
Individuals will adapt to new environments in order to survive. For example, these Pod Kopiste desert lizards were suited for catching small insects. When the researchers brought them to the island they adapted to their new surroundings and became mostly leaf eaters due to the abundance of fibrous plants. That's adaptation. The result of 30+ years of island life was an increased head size with an increased bite force and, more excitingly, the development of cecal valves in their digestive system (an entirely new structure to their bodies). And this occurred in the entire population. That's evolution.

It's worth reading. Apparently their behavior also changed because of the switch in their diet. They no longer had any use for predatory territory since they only preyed on insects opportunistically. Lucky bugs!
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Offline Jstwebbrowsing

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Re: Island lizards evolve..
« Reply #3 on: September 28, 2013, 05:07:09 PM »
Yes it is very interesting.  But what I've been told is the evolution works through random variation and natural selection.  In this case the variation doesn't seem very random.
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Offline none

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Re: Island lizards evolve..
« Reply #4 on: September 28, 2013, 05:22:25 PM »
isn't the move to a new island random enough?
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Offline Gilgamesh

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Re: Island lizards evolve..
« Reply #5 on: September 28, 2013, 06:54:25 PM »
But what I've been told is the evolution works through random variation and natural selection.  In this case the variation doesn't seem very random.

Ah! I think I understand what you're saying. Are you talking about the genetic changes displayed in the phenotype of the lizards, like the larger head and increased jaw strength?

You are correct- mutations are very random. Some help the organism adapt to its environment, some are neutral, and some can send the organism to an early grave (e.g. poor patterned camouflage). In this case with the Pod Kopiste lizards there was a random variation in head sizes and bite force. The lizards with the mutations for small heads and a weak bite force wouldn't be as well suited to their new environment to the degree of the lizards with the beneficial mutation for masticating the tough, fibrous plants. If an individual organism isn't as well suited then it won't be growing as quickly or reproducing as much as the rest of it's population.

To put it simply- because of the introduction of the new environment the larger heads flourished while the smaller heads died off or didn't reproduce as often, which lead to a gene pool that favored larger heads and increased bite force. That's why the variation doesn't seem random.
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Offline Tero

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Re: Island lizards evolve..
« Reply #6 on: September 28, 2013, 07:40:49 PM »
Mutations are random, but several mutations can go in the same direction. The mutations that went the other way may not have led to the animal dying, but it did not reproduce well. Females look for animals in good condition. If the male is skinny and barely surviving, she will not mate with it.

Every single step is tested, every generstion. It is the "drive" in evolution.

Was this too complicated, Browsing?

Offline Gilgamesh

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Re: Island lizards evolve..
« Reply #7 on: September 28, 2013, 08:28:24 PM »
Mutations are random, but several mutations can go in the same direction. The mutations that went the other way may not have led to the animal dying, but it did not reproduce well. Females look for animals in good condition. If the male is skinny and barely surviving, she will not mate with it.

Every single step is tested, every generstion. It is the "drive" in evolution.

Was this too complicated, Browsing?

In fairness, it is a little complicated. I had a rough time with it in my biology electives.
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Offline kevin

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Re: Island lizards evolve..
« Reply #8 on: September 29, 2013, 01:28:36 AM »
Individuals will adapt to new environments in order to survive. For example, these Pod Kopiste desert lizards were suited for catching small insects. When the researchers brought them to the island they adapted to their new surroundings and became mostly leaf eaters due to the abundance of fibrous plants. That's adaptation.

gilgamesh, your english useage is correct, but to use the term "adaptation" for a facultative behavioral change obscures its specific meaning with respect to natural selection.

sure, behaviour can be modified and fixed by selection, but the "adaptation" of an individual changing behavior is a different thing from the 'adaptation" of a population evolving a closer fit to a changing niche.
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Offline Gilgamesh

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Re: Island lizards evolve..
« Reply #9 on: September 29, 2013, 03:00:26 AM »
gilgamesh, your english useage is correct, but to use the term "adaptation" for a facultative behavioral change obscures its specific meaning with respect to natural selection.

sure, behaviour can be modified and fixed by selection, but the "adaptation" of an individual changing behavior is a different thing from the 'adaptation" of a population evolving a closer fit to a changing niche.

Can you elaborate on what you mean? I think I understand what you're saying, but it was a populations change in environment which lead to a change in behavior which lead to the populations evolution. I don't see why adaptation through behavior would be considered any differently in regards to natural selection.
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Offline kevin

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Re: Island lizards evolve..
« Reply #10 on: September 29, 2013, 01:46:18 PM »
You are correct- mutations are very random. Some help the organism adapt to its environment, some are neutral, and some can send the organism to an early grave (e.g. poor patterned camouflage). In this case with the Pod Kopiste lizards there was a random variation in head sizes and bite force. The lizards with the mutations for small heads and a weak bite force wouldn't be as well suited to their new environment to the degree of the lizards with the beneficial mutation for masticating the tough, fibrous plants. If an individual organism isn't as well suited then it won't be growing as quickly or reproducing as much as the rest of it's population.

To put it simply- because of the introduction of the new environment the larger heads flourished while the smaller heads died off or didn't reproduce as often, which lead to a gene pool that favored larger heads and increased bite force. That's why the variation doesn't seem random.

this ^^^ is what you said later, which is correct. what i picked up on was the idea that "adaptation" was something which individuals did in response to an environmental change that requires a shift in their resource utilization in some manner.

individuals don't adapt, only populations do. they do this by experiencing change in the gene frequencies of the traits undergoing selective pressure. for example, in your lizards, there will be pre-existing range of sizes and jaw structures, which are manifestations of heritable genes. if the distribution of food size or type changes, such that the optimum phenotype drifts away from whatever was stable before, then selection will track that change by favoring survival or fecundity of the organisms that possess the phenotypes better suited to the new distribution. over successive generations, the gene frequencies of the population will change, and evolution will have occurred. they may stay that way a bit, or continue to change, as they track the moving target of food types.

but no individual organism has adapted to anything, anywhere in the process. the individual organisms merely survive and reproduce at different frequencies, dependent upon their success in processing the change in their adaptive landscape.

now, you can use the term 'adaptation" in a completely different way by talking about behavioural changes in individuals. for example, if the range food types available to the lizards changes fairly slowly, then individuals can simply modify their choices of what goes into their mouths. this will not be a heritable change, and won't show up as an evolutionary modification. it can result in evolution, but isn't evolution itself, just flexibility. if the resource drifts far enough out of the range of the individual to process or moves too quickly, then the individual will suffer, and if the population phenotypic mean gets left behind by the resource change, then the population will suffer too, and may eventually go extinct.

that's all that i was saying.  and i'm not talking about mutation, just frequency changes among alleles that are already in the population. given mutation added to the mix, you can actually introduce things that are new, rather than just changing frequencies of things that are already there.
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Offline Gilgamesh

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Re: Island lizards evolve..
« Reply #11 on: September 29, 2013, 05:36:20 PM »
Ah now I see what you mean by obscuring its specific meaning in regards to natural selection! Makes total sense. Thanks for clearing that up.
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Offline Jstwebbrowsing

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Re: Island lizards evolve..
« Reply #12 on: September 29, 2013, 06:24:17 PM »
So what could have made larger heads and a stronger bite not be passed along in it's native habitat is what doesn't make sense to me.  It seem like a stronger bite would be beneficial for just about any animal?  Or at least I don't see how it would make them less fit to survive so as these lizards had not already evolved such things, but in 30 years in a different habitat they did.

I mean it seems to me if the variation was random then the randomness must have gotten it right the first time.  30 years is not long for "trial and error".
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Offline Gilgamesh

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Re: Island lizards evolve..
« Reply #13 on: September 29, 2013, 06:53:50 PM »
So what could have made larger heads and a stronger bite not be passed along in it's native habitat is what doesn't make sense to me.
I'm not a lizard expert but I would hazard a guess that a larger, heavier head wouldn't be ideal for catching the fast moving insects native to Pod Kopiste. But that's just speculation. It would make sense that the more agile lizards were better suited to catching prey in that environment.
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Offline kevin

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Re: Island lizards evolve..
« Reply #14 on: September 29, 2013, 07:52:02 PM »
jaws and teeth and so forth are designed and scaled to the prey that an organism hunts. look at the tiny delicate jaws of insectivorous bats, with their many needle-like teeth. they're designed to catch hold of insects in flight and retain them long enough for the bats to chew a bit and swallow. big heavy jaws don't hold an insect any better, and are heavier, with more bones and muscles.

but fruit bats likely have completely different teeth. i don't know this yet, and i'm going to look up images of both types to compare:

insectivorous bat:

Spoiler

this^^^ jaw is about 8 mm long.

fruit bat:

Spoiler


bingo. notice the great big fruit bat has completely different teeth, with grinding molars designed to crunch up plants that aren't struggling.

i didn't know this in advance. doesn't prove anything about evolution, but it illustrates how different types of teeth are necessay for eating different foods. the fruit bat mandible is about 50 mm long
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Offline Jstwebbrowsing

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Re: Island lizards evolve..
« Reply #15 on: September 29, 2013, 09:15:01 PM »
Yes that makes sense, but such considerable and advantageous change over such a short period of time, seems to really be beating the odds I would think.  Maybe I am just ignorant but that seems quite miraculous.
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Offline Captain Luke

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Re: Island lizards evolve..
« Reply #16 on: September 29, 2013, 10:09:21 PM »
30 years isn't much for humans. Lizards aren't humans.

Offline Jstwebbrowsing

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Re: Island lizards evolve..
« Reply #17 on: September 30, 2013, 12:55:40 AM »
They apparantly breed every spring so we're talking about 30 generations which would take humans about 600 years.
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Offline Mr. Blackwell

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Re: Island lizards evolve..
« Reply #18 on: September 30, 2013, 01:15:28 AM »
Yes that makes sense, but such considerable and advantageous change over such a short period of time, seems to really be beating the odds I would think.  Maybe I am just ignorant but that seems quite miraculous.

Maybe these things don't take nearly as long as previously suspected?
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Offline Airyaman

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Re: Island lizards evolve..
« Reply #19 on: September 30, 2013, 01:29:34 AM »
@ Jstwebbrowsing, how would you explain these changes in the lizard?
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Offline Captain Luke

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Re: Island lizards evolve..
« Reply #20 on: September 30, 2013, 10:37:02 AM »
They apparantly breed every spring so we're talking about 30 generations which would take humans about 600 years.
The breadth of generation is important too. One female could lay 30 or 40 eggs a year for several years, and each generation of new eggs could do the same. The exponential growth is significantly quicker that it would be for 30 generations of human. That allows for much quicker evolution.

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Re: Island lizards evolve..
« Reply #21 on: April 17, 2017, 03:32:05 PM »
How about inactive genes simply being re-activated?
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Re: Island lizards evolve..
« Reply #22 on: April 25, 2017, 03:25:26 PM »
Holy -necro!!!
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Re: Island lizards evolve..
« Reply #23 on: April 25, 2017, 04:01:00 PM »
Yes it is very interesting.  But what I've been told is the evolution works through random variation and natural selection.  In this case the variation doesn't seem very random.

but the natural selection is obvious.

edit:  OOPS!!  didn't realize how old the thread was...it showed up in my "unread" section today!
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Offline kevin

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Re: Island lizards evolve..
« Reply #24 on: April 25, 2017, 07:32:30 PM »
variation is always non-random.

my kids won't randomly be born with blue skin, or leathery wings.

perhaps a better description would be " distributed around a mean."
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