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natural selection

Discussion of everything related to the Theory of Evolution.

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natural selection

Postby disklutz1 » Wed May 03, 2006 5:47 am

Hello~I'm actually learning about it right now, and I'm really confused about the theory... so is it saying that as the environment changes, the ones who are able to adapt to the changes are able to survive, reproduce and carry on? And that by adapting, it means that the anatomy of the certain species changes gradually so that they are able to survive? What are the specific factors that determine this?
Any good examples?
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Postby AstusAleator » Wed May 03, 2006 10:02 pm

Well, since you're studying it, you'll no doubt be learning about Darwin's finches. They're a great case study as so much research has been done on them. If you've got the time/patience/curiosity to read a book, I'd highly suggest The Beak of the Finch by Jonathan Weiner. You should also check out The Island of the Color Blind. They're both pretty easy reads and you'll get an excellent understanding of natural selection, gene flow, island biogeography, and more.

As far as your question is concerned:
What you said in your question(?) is correct. That is the basic process of natural selection.
Natural Selection and adaptation USUALLY accompany environmental change. For example, if the average global temperature suddenly cools down by 10 degrees celsius, many animals would die off due to their inability to cope with climatic changes. Within a species, you may have 90% of the animals in the specie die off. The remaining 10% though, survive because they have traits that help them maintain their fitness in the new environment. When those 10% go on to reproduce then the traits that helped them survive will be passed on to their young, becoming a dominant trait in the population.
For example, we could say that only pigs with a lot of body hair survived the climate change. Then those survivors go on to reproduce, and because of phenotypic variability, their offspring will range from somewhat hairy to very hairy. The very hairy will be more fit in their environment and thus produce more offspring, so you will see a trend towards more hairyness. That scenario is an example of both gene flow and genetic drift.
I said USUALLY above, because I was using the term "environment" to mean the physical surroundings and phenomenon around an organism or population, ie weather, geology, water, etc. Ecologists include the biotic community into the term environment, to encompass everything in ones surroundings that can interact, be interacted with, or is observable.
A case where the physical environment does not need to change in order for adaptation to occur is in competition. The physical environment can remain stable, but as populations grow, organisms begin to compete with eachother. This usually leads to niche specification, or special adaptations to help an organism outcompete others.
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Postby disklutz1 » Thu May 04, 2006 4:39 am

^ thanks! but I still really don't get the idea of adaptation really well, so for example if an animal started to live near water they naturally might start forming webbed feet? how can this occur? as for the info on the books thanks!~ but how did the beaks literally evolve?

oh ps: and can you explain how the hardy-weinberg equilibrium shows an ideal population that is not evolving? like: 1. no mutations.. because so and so...

thank you so much!!
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Postby AstusAleator » Thu May 04, 2006 6:52 am

If an animal starts to live by water, it will not develop webbed feet.
Adaptations don't occur in an individual, but over the course of generations.
If that organism adopted a larglely aquatic life as its niche, then over the course of many generations, adaptations may cause the population to develop webbed feet.
Just remember that in natural selection, traits that increase fitness will persist, while those that decrease fitness or have a negligible effect are likely to be lost.
There is no force "driving" adaptation, just the environment "weeding out" unfit genes and/or phenotypes.
What did the parasitic Candiru fish say when it finally found a host? - - "Urethra!!"
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Postby sunnygirl » Mon Jul 31, 2006 1:56 am

so Natural selection annot occur unless individual members of a species differ from each other?

Is this right, according to natural selection, individuals cannot evolve new phenotypes in response to their enviroments?
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Postby canalon » Mon Jul 31, 2006 2:13 am

sunnygirl wrote:so Natural selection cannot occur unless individual members of a species differ from each other?


If there are no differences, then there is no selction for different genes, so no natural selection. Of course even if you start with an isogenic population, after a while mutations and other genetic events will make sure that differences are introduced, and natural selection will be playing with your population. As it has been shown among bacterial populations.

sunnygirl wrote:Is this right, according to natural selection, individuals cannot evolve new phenotypes in response to their enviroments?


Yes and no. It is known that some traits that are not expressed, yet latent genetically can appear if some environmental changes make them useful. But the environment will not create any genetic diversity that could be bred into the following generations.
Patrick

Science has proof without any certainty. Creationists have certainty without
any proof. (Ashley Montague)
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Postby sunnygirl » Mon Jul 31, 2006 2:42 am

ok thanks that cleared up some questions i had.


So when scientists classify creatures do they try and base them off of evolutionary relationships?
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Postby canalon » Mon Jul 31, 2006 3:36 am

Yes, or at least they try to.
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Postby James » Mon Jul 31, 2006 5:12 pm

Classifying organisms through evolutionary relationships is called cladistics, and can be shown through evoutionary trees.
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Postby sunnygirl » Mon Jul 31, 2006 11:03 pm

A "class" is a taxon of similar orders and a "phylum" is a taxon of similar classes, so is it true that if spiders and scorpions belong to the same class, then they must also belong to the same phylum?
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Postby James » Tue Aug 01, 2006 12:40 am

Yes, that's correct. You can imagine that their branches stem from a common branch on the evolutionary tree
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Postby sunnygirl » Tue Aug 01, 2006 12:45 am

What then is a kingdom? and how would you classify species into a kingdom?
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