What is the best resource for the current theory on evolution? Or to be specific, I have a few questions on it.
1) How many species of life are believed to have ever existed on Earth, in total, both extinct and current? This includes things like bacteria and viruses, which are still life, in essence, since they are organisms that did not exist when the universe was nothingness, do exist now, and reproduce to further their existence.
2) What various life-forms can reproduce a new species by breeding with an alternate species? I don’t mean like a mule, since even though a horse and donkey (which have different count of chromosomes) can reproduce, the offspring is generally sterile, and it doesn’t seem that mules can really breed on their own, so they aren’t really a new form of life.
3) How does a new species of life come to exist? This depends partly on #2, since my understanding is that in order to get a new life form that has a different set of genes and chromosomes from another, you would need to basically have two identical “mutationsâ€
Honest question about the theory of evolution
Moderators: NeilBlanchard, Ralf Hutter, sthayashi, Lawrence Lee
Well - I can answer one of these.
The most common way you get a new species is that you get more and more variation within a species (due to beneficial mutations) until at some point you start getting a high failure rate among members of the species that differ greatly. At that point, the likelihood of breeding with a "similar" member of the species is so much higher than breeding with a "different" one - that the subpopulations quickly diverge until the likelihood of breeding between them becomes essentially zero.
The most common way you get a new species is that you get more and more variation within a species (due to beneficial mutations) until at some point you start getting a high failure rate among members of the species that differ greatly. At that point, the likelihood of breeding with a "similar" member of the species is so much higher than breeding with a "different" one - that the subpopulations quickly diverge until the likelihood of breeding between them becomes essentially zero.
1) no-one really knows. estimates range from 1-50 billion. given the near-impossibility of reaching a comprehensive definition of what we mean by "species" and the length of time Earth (and life) has been around, this uncertainty is understandable.
2) the simplest definition of species is organisms that interbreed naturally in the wild and produce fertile offspring. so technically any organisms that fulfilled your criteria would be part of the same species.
2) the simplest definition of species is organisms that interbreed naturally in the wild and produce fertile offspring. so technically any organisms that fulfilled your criteria would be part of the same species.
seems logical enough to me: lots of things died, leaving their ecological niches unfilled (a free lunch as it were). nature abhors a vacuum, so lots of new species will come along to take their place.It seems contrary to scientific logic that the time periods of greatest spawning of new species happens after a great die-out.
wikipedia, although roundly denigrated by most, is more than averagely informative on these and similar topics.Where does one learn more about this?
Before answering any questions, people should precisely agree on the meaning of the words. How are we, SPCRians, going to discuss "species" when even biologists have difficulties coming up with a definition of species.
Look for the "species problem". Barely scratching the surface at the Wikipedia page for Species problem, read it if you want, but pay attention to the quotations on the difficulties of the problem and see how recent some of them are.
Pardon me for saying so but SPCR may not be the best venue to answer your question.
Look for the "species problem". Barely scratching the surface at the Wikipedia page for Species problem, read it if you want, but pay attention to the quotations on the difficulties of the problem and see how recent some of them are.
Pardon me for saying so but SPCR may not be the best venue to answer your question.
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N7SC
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1. No one really knows, the range of guesses is pretty wide, and new ones are discovered frequently.
2. Quoting from "Biology The Science of Life" by Wallace, King and Sanders,
"The general definition of species is any group of organisms that could interbreed. The definition works will in many situations but is very argumentative in others.
A. Some well-defined species do interbreed under labratory conditions
B. Some might interbreed if they were not separated by barriers.
C. Some specices interbreed along a cline, but not between the ends of the range, even under laboratory conditions."
3. Actually the answer to this does not depend on your question #2. It is a process called speciation. The simplest answer I can give would be that a population of a single species must be somehow reproductively divided. That is the two pools of individuals must not be able to reproduce with each other. Second, then two groups must then be subject to differing selective pressures. This will cause a change in allele frequencies in the two different groups, and possibly the introduction and survival of new alleles that were not present in the orignal species. When the two groups diverge genetically enough that they can no longer interbreed with each other even if the barrier to reproductive mixing is removed, then you have a (or two) new species. (warning: vastly oversimplified explaination)
A great start on the subject would be to read the appropriate sections of a college core biology text. By Core, I mean the biology sequence that is for graduate students, pre-professional students, etc. Not the ordinary biology program for everyone else, like business majors, that just needs the bio credits to meet graduation requirements. One example that I particularly love is the above quoted "Biology The Science of Life" by Wallace, King and Sanders. 1st edition ISBN: 0-673-15591-9 It was what I used in my undergrad years and is very well written. You can get it via Amazon for about $8 or $9, including shipping. Although the newer editions are by Wallace, Sanders and Robert Ferl (whom I had as a professor - he was bland). IMHO the older editions by WK&S are the best written ones.
2. Quoting from "Biology The Science of Life" by Wallace, King and Sanders,
"The general definition of species is any group of organisms that could interbreed. The definition works will in many situations but is very argumentative in others.
A. Some well-defined species do interbreed under labratory conditions
B. Some might interbreed if they were not separated by barriers.
C. Some specices interbreed along a cline, but not between the ends of the range, even under laboratory conditions."
3. Actually the answer to this does not depend on your question #2. It is a process called speciation. The simplest answer I can give would be that a population of a single species must be somehow reproductively divided. That is the two pools of individuals must not be able to reproduce with each other. Second, then two groups must then be subject to differing selective pressures. This will cause a change in allele frequencies in the two different groups, and possibly the introduction and survival of new alleles that were not present in the orignal species. When the two groups diverge genetically enough that they can no longer interbreed with each other even if the barrier to reproductive mixing is removed, then you have a (or two) new species. (warning: vastly oversimplified explaination)
A great start on the subject would be to read the appropriate sections of a college core biology text. By Core, I mean the biology sequence that is for graduate students, pre-professional students, etc. Not the ordinary biology program for everyone else, like business majors, that just needs the bio credits to meet graduation requirements. One example that I particularly love is the above quoted "Biology The Science of Life" by Wallace, King and Sanders. 1st edition ISBN: 0-673-15591-9 It was what I used in my undergrad years and is very well written. You can get it via Amazon for about $8 or $9, including shipping. Although the newer editions are by Wallace, Sanders and Robert Ferl (whom I had as a professor - he was bland). IMHO the older editions by WK&S are the best written ones.
Last edited by N7SC on Mon Jan 28, 2008 2:09 pm, edited 2 times in total.
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N7SC
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P.S. I'd recommend avoiding Wikipedia on this type of adventure. You want something that is well-vetted by reviewers that are established experts in the field. A good college text fills the bill here. Further, the style of a good text is going to be designed to be for teaching. And, the book will contain a whole lot more than just the section on evolution and genetics (Wallace, King, and Sanders is about 1200 pages!). So you can learn all of the intricate and interlocking details of biology in one place, presented in a logical sequence and with some coherence.
Also, do avoid reading Darwin's "The Origin of Species." It is a quaint, and very old, book. Very full of the incredibly brilliant reasoning that led to the theory of evolution, but really more of a novelty than a good teaching text. You may find it fun after you read a college text and have some knowlege, but not to really learn from.
Also, do avoid reading Darwin's "The Origin of Species." It is a quaint, and very old, book. Very full of the incredibly brilliant reasoning that led to the theory of evolution, but really more of a novelty than a good teaching text. You may find it fun after you read a college text and have some knowlege, but not to really learn from.
Re: Honest question about the theory of evolution
I'll expand a bit on the "free lunch" reasoning above. A great die-out will leave a lot of niches open for new creatures. A current and varied population of one species might be able to fill several of these niches, and will therefore get several different directions in which evolving is beneficial. Since there is a lot less competition for resources, creatures can "allow" themselves more "frivolous" changes and still make it, which puts less strain on a genetically homogenous population and allows more variation.AZBrandon wrote:It seems contrary to scientific logic that the time periods of greatest spawning of new species happens after a great die-out. I would think that the time when the most new species come into existence would be when you have the highest number of creatures roaming the Earth, not the times when it was the least number of creatures. Where does one learn more about this?
Not really - the basic idea of evolution is pretty simple, and intuitively obvious once somebody points it out. (It is the framing it in the first place that took a lot of hard work.)Thanks for all the info, it looks like there's good reason why it's not a well understood theory - so complex that even scientists can't agree on what a species is!
The difficulty in how to exactly define a species is more because you are trying to give a discreet categorization to something that is a continuous, analog mess. (For instance, the simple ideas of species being defined by reproductive isolation totally go to pot if you start looking at kingdoms other than animal. The plants can have sex lives that make soap opera folks look like monks.)
Organisms don't care about what species they are, they just do what they do, and some of it works and some of it doesn't.
Which isn't saying that species is a useless concept, but no point in getting bogged down in the details, unless you are going to specialize in it.
So if you don't worry about the fine edges, evolution is pretty easy to understand.
If you have reproduction with variations that can be passed on to offspring, and limitations on survival/reproduction (limited resources, isolated groups, breeding preferences, whatever). Then given enough generations you are likely to get offspring that vary greatly from their early ancestors, and from other offspring. (See, you don't even need to use species, if you don't want to.
Same concept works for ideas, technological artifacts, or biology.