Primitive snakes - Page 8

tdherper · 01-31-05, 10:19 AM

PS It was fated when they wrote that jingle .... it would apply to this situation.....they/we just didn't know it at the time.....

JimmyDavid · 01-31-05, 10:40 AM

hahahaha, you made my day. Great humor.
(and so very right)

Double J · 01-31-05, 10:41 AM

Quote:

Originally posted by JimmyDavid

A het is not the real thing

Jimmy.... a heterozygous individual is absolutely a real thing. Heterozygous, on a most basic level, this refers to the condition of one carrying two alleles of the same gene. In the case of a heterozygous individual, you can have either allele being dominant and/or recessive with the expression of one or the other, or in some cases, a heterozygous individual may express a sort of blending of the traits of the alleles on that gene. Again, this is incredibly simplified.
A het is not a real thing?????? Jimmy.... again this shows how poor your knowledge of genetics and evolution is. READ A TEXTBOOK!!!!!!! Organisms that are heterozygous exist! This is not a man-made model, it is real!

Quote:

Originally posted by JimmyDavid

I don't know how manny of you have info about the Chaos theory, but the more you learn about it, the more you suspect "convenient" probabilities like beneficial mutations.

Ps _ Also take in consideration that there's a natural tendency in species to breed with familiar looking specimens. That's why Hybrids are rare to obtain. A
creature that looks or acts different within a population probably will never get an interested breeding partner. Once again chances for a mutant to keep going don't look good.

Food for thought: You guys make it sound easy that a new species rises from a single specimen; scientists consider a species is doomed when numbers are reduced to a few thousands. Compare the odds.....

Jimmy... I cannot stress this enough.. so I will type it in caps this time...

NOT ALL ADAPTATION AND/OR EVOLUTION IS A RESULT OF RANDOM MUTATION!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

I will say it one more time so it sinks in:

NOT ALL ADAPTATION AND/OR EVOLUTION IS A RESULT OF RANDOM MUTATION!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Okay, read this carefully. There is a range of varation and variability for any number of traits in a population. Thus, going back to giraffes in an extremely simplified model.... in the process of their evolution, some giraffes have longer necks than others. Therefore, you can have animals of similar general body size, with varying lengths of their necks. Giraffes A, B, C, and D have necks ranging from say 7-9 feet. Giraffes E, F, G, and H have necks that range from 4-7 feet. We will say then, that all of these animals are within a few months of each other in terms of age, and are within a few months of sexual maturity. To continue, perhaps we can now imagine that the past few years have been realtively prosperous for the giraffes in terms of reproduction, so the population has risen by X percent. However, the carrying capacity of the savannah and the acacia trees which they feed on cannot support this many animals. As this increase in population feeds, the lower leaves on the acacias have thinned out. There are then far fewer leaves on the lower portions of these trees. However, giraffes A through D, through the simpleness of species variability, (they are fortunate in this case of course) to have necks that are a few feet longer than individuals E through H. Now, there is a shortage of low-growing acacia trees from heavy feeding from a high population. Much of the lower growth is now gone. Giraffes A through D have little trouble reaching higher into the acacias for leaves. Giraffes E through H however, are having trouble finding food at this point, and have to wander farther and wider for food... though giraffe H may be able to scrounge a little more than the others on the lower end of the neck length range as his neck is in the middle of the range (7 feet). Thus, giraffes E, F, and G have starved because they could not reach higher into the trees, while giraffes A through D, as well as maybe E are able to live through this harder season, outcompete these shorter necked individuals, and reproduce a few months later. So, in this model, the giraffes with slightly longer necks have been selected for, as they have had an edge in this case of exploiting a resource like food. They then, have passed on the genetics for slightly longer necks. Again, this is not a result of mutation!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Rather it is a result of selection of individuals at one extreme of a *range of variability.* This does work both ways as well. There is a limit to how beneficial a long neck can be, and this will often be controlled as well. Now, let's not forget that there will still be variation in subsequent generations, though it will tend to be to the higher necked end of the spectrum. However, this is controlled as well. This process is called NEGATIVE FEEDBACK. This works to keep variability within a range. Giraffes with necks that were too long may have had problems drinking water early one, or may have had problems running, or even skeletal or muscular problems that would lead to death before reproduction. Thus, the biology of the animal itself may limit the range of variability as well. And of course, the animals with the shorter necks on the extreme end of variability may have problems feeding at a young age, and then may not reach reproductive age. However, this variability with a low end of the spectrum is beneficial as well. For some reason, if there was a beneficial reason to have a shorter neck for feeding on the ground.... say acacia trees were wiped ourt by some sort of disease or climatic change, there is the variability within the giraffe population to go back to a shorter necked population if need be.
This does not always work though, though varaibility allows you to deal with a change, not enough variability, or a change that occurs too fast in the environment may lead to extinction.

I hope this simple model allows you to realize that not all adaptation and evolution occurs through random mutations.

Double J

JimmyDavid · 01-31-05, 10:51 AM

Quote:

Originally posted by Double J

I hope this simple model allows you to realize that not all adaptation and evolution occurs through random mutations.

Double J

Well, that's been what i've struggled to say. Isn't it!!??

Evolution through genetic combination sounds more logical. Still, it doesn't explain everything, notice that genetic mixing within a population has more of a tendency to LEVEL and not ADD UP. When 2 giraffes breed, one will have a longer neck than the other; the offspring will lickely have a neck lenght that's between both. You can say that the more a species breeds, the more it searches for a stable form of it's own.
And Don't forget that an asexual creature evolves as well. How do you explain that?

CamHanna · 01-31-05, 10:55 AM

Perhaps albinism wasn't a good example as it is not a beneficial trait.

Melinism in Ontario's eastern garter snake is a simple recessive mutation that is quite common in some populations. Presumably a black snake is at an advantage because it can warm up faster and thus reduce it's basking time and increase it's chances of survival. Because it is beneficial the mutation has proliferated.

It's true that hets won't have the same benefit as homos but also, a het is no worse off than the rest of the population. When it breeds to a normal a het produces 50% hets. Certainly not all the hets will survive to adulthood but likely some will and eventually two hets are likely to breed together. If the homo form is successful then it will either produce more hets when bred with a normal or more homos when bred with a homo (or het). This all occurs in wild eastern garter snake populations.

Like Cake pointed out there are patterns of heritability at play as well.

I should also point out that one successfull mutation doesn't make a new species, only a new morph. To make a new species it takes many, many mutations. So many that the new species no longer interbreeds with the old species.

A mutated animal likely won't have trouble finding a mate should it survive to adulthood. Melinistic garter snakes is one example but perhaps corn snakes are a more familier one. A captive albino-motley-anery-lavender will readily breed with a normal. I'm sure that if the two met in the wild (though there aren't many wild a-m-a-l corns) they would be just as likely to breed.

A species is defined as a group of individual that will interbreed. So, once our 'mutant' group no longer breeds with the normal group it is a new species. Speciation, like I said earlier, takes place after many, many, many small mutations.

I should point out, like Double J did, that not all 'mutations' (i've used the word loosely), are as simply as melinism. The giraffe example is a good one where neck length is probably dependent on a number of genetic influences but none-the-less is passed to the offspring.

Cam

Removed_2815 · 01-31-05, 10:58 AM

Quote:

Originally posted by JimmyDavid
Well, that's been what i've struggled to say. Isn't it!!??

No, and I think you've missed the point again.
Mutations are the source of all genetic variation. Genetic variation refers to the genetic heterogeneity in a population.

Ryan

JimmyDavid · 01-31-05, 11:04 AM

Quote:

Originally posted by CamHanna

I should also point out that one successfull mutation doesn't make a new species, only a new morph. To make a new species it takes many, many mutations.

Cam

Now there a agree totaly. And that's what makes one think what are the odds that another mutation comes along to continue EXACTLY the work started by the previous.

JG20 · 01-31-05, 11:08 AM

Wow, that was a great read. All eight pages, so far...

JimmyDavid, you're totally missing it. There's no documented evidence of an individual/organism changing it's genetic compositon or that of it's gonads through physiological, metal, or whatever type of training. If there was, then the whole evolutionary theory would be shot down.

BTW, evolution is both a theory and a fact. It is fact because it is occuring as we speak (err type). Speciation is happening in front of our eyes. However, since we cannot prove the past, evolution is the theory of how we (ie all living things) came to be.

RMBolton, Double J, Cake, CamHanna, etc. have already gone through the points so I won't bother but take their advice, do more reading on the subject. If you can find any evidence of an individual able to change it's genetic makeup, I'm sure, we would al be changing our minds and so would the rest of the scientific community.

Joe

JimmyDavid · 01-31-05, 11:16 AM

Can't argue with that!
But i'm a believer that it can happen. Perhaps one day we'll know.

So far, it's know to be possible that a creature undergoes a somatic genetic change through it's life. That means it changes it's own genetics, only can't pass it to it's offspring. Maybe the future will tell us how much that influences a germlike mutation as well (so far, thought to be impossible).

CamHanna · 01-31-05, 11:25 AM

Quote:

Posted by JimmyDavid
So far, it's known to be possible that a creature undergoes a somatic genetic change through it's life.

Are you refering to cancerous mutations or do you have some other evidence?

JimmyDavid · 01-31-05, 11:28 AM

Animals that change sex through the course of it's life, for example.

Removed_2815 · 01-31-05, 11:28 AM

Quote:

Originally posted by JimmyDavid
That means it changes it's own genetics

Sorry, but no. Mutations in somatic cells are caused by radiation, carcinogenic chemicals, or transcription errors. Someone already mentioned this here when discussing cancerous tumours. The "creature" certainly does not change its own genetics.

Ryan

JG20 · 01-31-05, 11:30 AM

Quote:

Originally posted by JimmyDavid
So far, it's know to be possible that a creature undergoes a somatic genetic change through it's life. That means it changes it's own genetics, only can't pass it to it's offspring. Maybe the future will tell us how much that influences a germlike mutation as well (so far, thought to be impossible).

Again, not proven. You're gonna have to provide some sort of literature behind this claim. Could you refer me to a textbook, published article or journal that claims this?

Joe

JimmyDavid · 01-31-05, 11:31 AM

Creating an extra gene and changing from male to female is a genetic change.

Here, i found a site on that:
http://www.crystalinks.com/biology2.html

But there are lots of cases involving populations of frogs, fish and certain anphibians.

Removed_2815 · 01-31-05, 11:36 AM

Quote:

Originally posted by JimmyDavid
Animals that change sex through the course of it's life, for example.

Again, sorry, but no. This is not a change of genetics.
The foetuses of all vertebrates develop with elementary forms of female and male genitalia, and the potential to develop one or the other. In most vertebrate species, the genetic sex of the organism dictates whether the foetus develops male or female genitalia, while the other gradually diminishes and disappears.

However, in several species, females grow female genitalia normally, while the elementary male genitalia is maintained for later development (potentially). External stimuli cause changes in the female's hormone levels (such as the death of the primary male in certain Cichlids), eliciting the male genitalia to begin maturing.

Ryan