Evolution of mammals
Posted on: February 9, 2011 - 11:48pm
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Evolution of mammals
At what point in the evolution of reptiles did they go from laying hard shelled eggs to keeping the egg in the body.
In otherwords how did this happen one generation lays eggs and then the next doesnt that seems kinda strange.
Did it go something like the eggs where getting eaten and the animals that didnt lay eggs reproduced better.
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Is what I brought up about populations seperating what happened to asian people being in different locations so they went in their own direction mutation wise, is this right its not tha there eyes being different actually has a function. Also if I can't call them race waht can I call them?
Again, from Wiki:
-- I feel so much better since I stopped trying to believe.
"We are entitled to our own opinions. We're not entitled to our own facts"- Al Franken
"If death isn't sweet oblivion, I will be severely disappointed" - Ruth M.
Those are geographic/national boundaries. That doesn't bother me, why should it? You want to refer to "people in Asia" - fine. "People in Africa" - great. "Nordic peoples" - why not?
I object to "races" as ALL traits are expressed in all populations. And "race" has been used as a way to put people down. It is not accurate and it is hurtful. Let the word die.
I'm not real happy when filling out a form and it asks - white (caucasian), black, American Indian, etc. And then some of them go on and ask if you are Hispanic and what nationality - Cuban, Mexican, Puerto Rican, etc. I will fill it out, but I do wish it wasn't true that "people of this background <make less><have worse health><whatever else>". Then we quit asking the question because it no longer told us anything.
As it is now, people are classified and treated differently based on physical characteristics they have no control over.
-- I feel so much better since I stopped trying to believe.
"We are entitled to our own opinions. We're not entitled to our own facts"- Al Franken
"If death isn't sweet oblivion, I will be severely disappointed" - Ruth M.
I totally agree with you about the race thing but I was talking from a Taxonomy perspective.
OK, race is not a term which is useful on the level of determining social policies. For that, the matter is balls useless. On the other hand, there are “racial traits” which may have some relevance when any of us are in the doctor's office.
As we all know, showing up at the doctor with a certain set of symptoms does not automatically clinch the diagnosis. If that were the case, then doc would not have to order tests to get other useful information.
That much being said, there are certain conditions for which race is relevant. One that is of some interest is sickle cell disease. Generally, only those of African descent get it. However, that is not absolute as I will explain.
You see, as BobSpence observed, recessive genes generally do not manifest unless an individual has two copies. So those with one copy of a recessive gene are only carriers of the trait. As the gene for sickle cell disease is recessive, it can turn up pretty much in any population. I would have to do some googling on the matter but from what I remember, there are a few individuals with full blown sickle cell disease who come from native Icelandic stock. Because the gene has existed long enough that it has had time to travel there through the slow process of village to village transfer.
That being said, it would raise the question of why it would be more common in Africa than elsewhere. Here is the rub: Apparently, the gene (or another one that is closely associated) is dominant for Malaria resistance. So nif you have one copy, you have a better chance of not getting that disease. At least if you live in the tropics.
Thus, there is a selection pressure for the gene in Africa, provided that you don't get two copies. In that case, you will not likely live to have kids regardless of the fact that you can survive a bite from a tropical mosquito.
On the other hand, the selection pressure in Iceland is different. Since the anopheles mosquito does not live there, getting two copies of the gene is a bad thing but simply having one copy and continuing to pass it on means nothing. So there is no huge pressure for the recessive single gene to die out.
One idea that would be worth looking into would be if the disease is showing up in the Hispanic population of South America. After all, the gene is somewhat wide spread and malaria exists there. If the pair of traits is turning up in a population that may retain the gene in single copy individuals and those people have since moved into an area where the gene becomes relevant, then it should reassert itself.
Meh, someone else can google for that if they wish.
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