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Author Topic: What is Darwin’s explanation of how new species arise in simple terms?  (Read 13684 times)

Offline echochartruse

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Natural selection Doesn't explain how a totally new speicies arises - to me. It seems to me that he is discribing a species that has altered slightly in some way, possibly through epigenetics or other to proceed where the same species of previous generations did not change, had no need to change. Where the ancestors of say, turtles an entirly different species or a variation of the same species? - appology for too many questions, just trying to understand

Can someone with knowledge of Dawin's theory please explain how a new species arises in the simplist terms?
« Last Edit: 30/03/2010 18:14:11 by echochartruse »


 

Offline Geezer

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I understand the theory says new species arise through natural selection. It's a question of time. We are talking about time intervals that are incomprehensible from human experience.

I'm no expert in this field, but I assume what happens is that over a long enough period, related groups become incapable of interbreeding because they are prevented from interbreeding through isolation, or some physical change that makes it impossible. Then over a long period of time, their genes diverge sufficiently that interbreeding becomes impossible. At that point, you have a new species.

Are horses and donkeys different species? I tend to think they are. They can interbreed to produce a mule, but there will never be a species called "mules".  Mules, are incapable of breeding. 
 

Offline PhysBang

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It seems to me that he is discribing a species that has altered slightly in some way, possibly through epigenetics or other to proceed where the same species of previous generations did not change, had no need to change.
All populations of organisms have some variety and new variations enter into the population all the time through mutation. If there is no pressure from the environment that makes one variation significantly different from another, then there will be no change in the average individual in the population over time. If something in the environment makes it so that one or two variations are significantly different (and better able to survive), then over time the average individual in a population will change accordingly.

Small changes in variation can build up over time.
 

Offline echochartruse

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..... I assume what happens is that over a long enough period, related groups become incapable of interbreeding because they are prevented from interbreeding through isolation, or some physical change that makes it impossible. Then over a long period of time, their genes diverge sufficiently that interbreeding becomes impossible. At that point, you have a new species.

Are horses and donkeys different species? I tend to think they are. They can interbreed to produce a mule, but there will never be a species called "mules".  Mules, are incapable of breeding. 
what are you refering to as 'related groups' please?
when you say interbreeding are you speaking of breeding between different species?
 

Offline echochartruse

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All populations of organisms have some variety and new variations enter into the population all the time through mutation. If there is no pressure from the environment that makes one variation significantly different from another, then there will be no change in the average individual in the population over time. If something in the environment makes it so that one or two variations are significantly different (and better able to survive), then over time the average individual in a population will change accordingly.

Small changes in variation can build up over time.

I agree that small variations do change (such as children from their parents) but I truely dont understand how a new species arises from this.
 

Offline BenV

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Was it just the same species doing adaptaions to the surrounding environment? Did an entirely new species come from another species?
Essentially yes, but you shouldn't get hung up on the idea of different species.  "Species" are, after all, just labels that humans put on different things.

did the kangaroo climb a tree to become a possum then decide to climb down and becoem a rock wallaby? then why didnt they all become possums?

There was once an ancestor of all these animals.  Some of these (for whatever reason) spent more time in the trees - this population were then subject to the selection pressure of arborial life, and eventually became the species we now call the possum.  Other populations of this ancestor species moved into other environments, and different selective pressures acted.

Survival of the fittest, why didnt they all become one species what changed some to be another species, dont they know humans are top of the evolution chain.

This is due to the fact that several different things can be the "fittest" for different ways of life in the same area - each one specialising towards a different way of life.

Humans are not special - we're not top of the evolution chain - every extant species is the pinnacle of evolution.

That's it in a nutshell.

Populations change over time.  Given enough time and enough pressure (and things like the founder effect/bottleneck effect), these populations will become no longer able to breed with one another.  We then call them new species.

It honestly is that simple.
 

Offline rosy

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I agree that small variations do change (such as children from their parents) but I truely dont understand how a new species arises from this.

Basically it usually involves a separation of the two groups, often physically. If two groups of individuals of the same species are put in two different places, such that they don't (or don't often) meet, then over many generations the small parent-to-child changes will accumulate and eventually the two groups will no longer be able to interbreed. Does that make sense to you? In some cases the groups will be subjected to selection pressures which will mean that different characteristics are favoured (say an ability to run fast and escape predators in one case, and a long nose to get food out of the ground in another), so they'll end up looking different and with different habits, but that's not really necessary for speciation.. simple random changes over time without interaction between the groups is sufficient.
It's not complicated it's just that it typically takes quite a lot of generations.
 

Offline echochartruse

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......... you shouldn't get hung up on the idea of different species.  "Species" are, after all, just labels that humans put on different things.

Still trying to get my head around this.... what does the label 'species' refer to?
 

Offline echochartruse

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Basically it usually involves a separation of the two groups, often physically. If two groups of individuals of the same species are put in two different places, such that they don't (or don't often) meet, then over many generations the small parent-to-child changes will accumulate and eventually the two groups will no longer be able to interbreed. Does that make sense to you? In some cases the groups will be subjected to selection pressures which will mean that different characteristics are favoured (say an ability to run fast and escape predators in one case, and a long nose to get food out of the ground in another), so they'll end up looking different and with different habits, but that's not really necessary for speciation.. simple random changes over time without interaction between the groups is sufficient.
It's not complicated it's just that it typically takes quite a lot of generations.

Am I right saying that if humans refained from travel and mixed race marriages then it is possible a new 'species' would evolve over time?
« Last Edit: 30/03/2010 22:00:38 by echochartruse »
 

Offline echochartruse

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Populations change over time.  Given enough time and enough pressure (and things like the founder effect/bottleneck effect), these populations will become no longer able to breed with one another.  We then call them new species.
I dont understand if they are 'no longer able to breed with one another' how are they able to survive if not able to reproduce over vast periods of time? How do they quickly find an individual they can breed with?
 

Offline BenV

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Populations change over time.  Given enough time and enough pressure (and things like the founder effect/bottleneck effect), these populations will become no longer able to breed with one another.  We then call them new species.
I dont understand if they are 'no longer able to breed with one another' how are they able to survive if not able to reproduce over vast periods of time? How do they quickly find an individual they can breed with?
Ah, I see your confusion - I'm talking about populations, not individuals.

Yes, if human populations were separated for a sufficiently long time, with enough selection pressure, it's possibe that these populations would no longer be able to breed, and we would define them as new species.
 

Offline BenV

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......... you shouldn't get hung up on the idea of different species.  "Species" are, after all, just labels that humans put on different things.

Still trying to get my head around this.... what does the label 'species' refer to?
There's a few different definitions, but the broadest and most convenient is just two populations that cannot breed to have viable offspring.
 

Offline BenV

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Am I right saying that if humans refained from travel and mixed race marriages then it is possible a new 'species' would evolve over time?

It's worth noting that "race" may not be the best indicator of genetic difference.
 

Offline echochartruse

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Am I right saying that if humans refained from travel and mixed race marriages then it is possible a new 'species' would evolve over time?

It's worth noting that "race" may not be the best indicator of genetic difference.

No, No, I hope you dont think of me as racist.........

Maybe I misunderstood you.

If a population is segregated (say distance, location, whatever) and the environmental factors of each group differ, then over a long period of time, this same 'species' would not be able to breed together becasue of it. Becasue each group would develop differently? is that what you are saying?
 

Offline BenV

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In very broad strokes, yes.
 

Offline echochartruse

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There's a few different definitions, but the broadest and most convenient is just two populations that cannot breed to have viable offspring.
Wouldn't it just be: each segregated group only able to breed within their group as they evolve? I dont see how this creates a separate 'species'
 

Offline Geezer

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Ah! Right, "populations" is a better term.

Consider this hypothetical example.

There is a population of elephants on a big island. Gradually, sea level rises, and the island becomes two island, leaving some elephants on one, and some on the other. The food supply on one island happens to favor small elephants, other way round on the other island. Over time, the two populations will differ greatly in size.

Now, it's quite possible the two populations are genetically compatible, so they could possibly reintegrate. However, because they are now very different in size, interbreeding by natural means is impossible. Technically they are still a single species, but because of mutations, unless they somehow figure out a way to interbreed, over time they will become two different species.
 

Offline echochartruse

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Ah! Right, "populations" is a better term.

Consider this hypothetical example.

There is a population of elephants on a big island. Gradually, sea level rises, and the island becomes two island, leaving some elephants on one, and some on the other. The food supply on one island happens to favor small elephants, other way round on the other island. Over time, the two populations will differ greatly in size.

Now, it's quite possible the two populations are genetically compatible, so they could possibly reintegrate. However, because they are now very different in size, interbreeding by natural means is impossible. Technically they are still a single species, but because of mutations, unless they somehow figure out a way to interbreed, over time they will become two different species.

Sorry this is what I have trouble with. Wouldn't they be the same species still just hybridised?
Birds for example, I never see them interbreeding, except for human influence or I haven't heard of it otherwise, but they are still the same species.
 

Offline rosy

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Wouldn't it just be: each segregated group only able to breed within their group as they evolve? I dont see how this creates a separate 'species'
Perhaps a concrete (wholly fictional) example might help?
A definition of what is required for two populations of similar animals to be considered to be different species is for them to be unable to interbreed. Interbreeding allows genetic material to be shared across subsequent generations, so the two populations won't diverge significantly in their characteristics, but once this has ceased (and it is generally because the populations are moving in different areas that interbreeding stops) there is no check on the effect of random genetic changes (and where applicable differing selection pressures) causing those two groups to diverge further even if they return to living in the same environment.
Speciation is hard to pinpoint, because sometimes you could in principal get a population of animals living on one side of a mountain range, which differ sufficiently from another population on the other side to be unable to interbreed (perhaps one group has got much bigger than the other and the small males can't mount the large females but the small females can't carry the large offspring of the large males), but yet a third group of medium sized animals living in the mountains could exist which can interbreed with both groups. If the medium sized animals were killed off by a few very harsh winters, the large and small populations would then become seperate species, and their future evolutionary pathways wouldn't be influenced by interbreeding with their cousins from over the hills. But if the population of humans on either side of the mountains drove both groups further up into the hills so they met and interbred more often with the medium sized animals, then those animals which had the widest choice of mates would tend to do well, which would work in favour of the medium sized animals and against the extreme differences which might prevent successful offspring of mixing.
I think this explanation would make more sense if it weren't so late at night here.. apologies if it's incomprehensible.
 

Offline rosy

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Hmm, preempted by Geezer's better explanation, but I post anyhow.

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Birds for example, I never see them interbreeding, except for human influence or I haven't heard of it otherwise, but they are still the same species.
Sorry?? I'm not sure if this is what you meant. If it is - there are many, many different species of birds! "Birds" is a very general class like "mammals" or "fish". If this is news to you I'm not surprised you're struggling with evolution, and indeed am very impressed you're trying!
 

Offline echochartruse

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Rosy, I think my mind is blocked with the word 'species' still.
Can you give me an example in real life terms, 2 distinct unrealted 'species' interbreeding?
I still see it as hybridisation of a 'species' Sorry.

Oh so now I also understand that 'species' is not associated with just the appearance, such as birds, thanks. Which is probably why they dont interbreed, is it?

Why dont different 'species' interbreed? I suppose I should understand one thing before I ask another question.
 

Offline rosy

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Why dont different 'species' interbreed? I suppose I should understand one thing before I ask another question.
Sometimes they try, but if they're sufficiently different they don't succeed. That can be for lots of reasons, one of which is that cell biology is incredibly subtle, your genes tell your cells which proteins to it can make and lots of things (the initial condition of the cell, external factors, which other genes are "switched on") will determine how much of what. That's an astonishingly fine balancing act and depends on lots of interacting systems which have to have their feedback loops just right to work at all.
When a sperm meets an egg, some of the genes from each of the mother and father (assuming they recognise each other, which in sufficiently different species they won't) are combined to make the first cell of the new individual. That cell then starts making proteins, if the balance of the proteins its genes are telling it to make are wrong, it won't survive. It will never make it to the stage of being a reproductively viable individual.
In very closely related species (like horses and donkeys) the offspring may be a pretty successful individual in terms of its own survival, but unable to breed, in other combinations the egg may just never get fertilised. In some cases, where two populations haven't interbred much and they've got quite a long way apart from each other in terms of genetics, it might be that interbreeding between the two populations is only very rarely successful, but some can survive, and if those individuals go on to breed successfully it could lead to the formation of seperate species being prevented because more breeding between groups becomes possible. It's all very smudgy round the edges. As is my brain, it's too late at night and I should be in bed! Night all. 
 

Offline echochartruse

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Rosy after I last wrote I thought for a while and became totatlly confused. Now reading your last post it has made so much more sense. I still have lots of questions but need to fully digest and filter the questions I have in hope that most are answered. thank you
 

Offline echochartruse

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If because of some environmental influence my children were born without legs and instead grew stumps and their children and generations after generations due to the non changing environment were born the same would they would be mutants/hybrids of the same species?

So what I understand is that there has to be interbreeding between 2 or more distinct groups so distant related that you could say they are ‘separate species’ I would suppose that would mean that each group did not share, say the same ancestral mother.

With Domestic cats such as the Bengal breed it is not a specific new species only a hybrid.

I can’t think of any example of a new species that has been influenced by humans, can someone help me here. As I’m thinking if we can hybridise a species we could possibly create a new species.
 

Offline JP

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Domestic cats are a different species than their wild counterparts, as far as I know.  (Dogs, however, can interbreed with wolves and therefore aren't a separate species.)  Other domesticated animals or plants might be separate species from their wild counterparts as well.

Domestication is an example of humans helping an organism with certain mutations survive and continually selecting for offspring with more favorable traits for domestication.  Eventually enough mutations accumulate that a new species arises.

There's also a new field called synthetic life, where the goal is the creation of life (and new species) by building single-celled organisms in a lab.
 

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