Evolution By Natural Selection

[Dean]

Evolution By Natural Selection -- A Discussion of The Basics

With the interest of a couple of individuals, such as WarK and theyounghistorian77 - along with (possibly) Hytegia - I open this thread to invite general discussion of the basics of Evolutionary Biology - anything and everything to do with modern evolutionary theory. This was also accentuated by the fact that evolution happens to be my favourite subject in the whole woooorld!

Hopefully, this could also offer a launch-pad so to speak, for anyone who is as of yet uncertain about the subject of evolution, to get a decent understanding of it.

 

[Dean]

Edit: Also - I recommend Dawkins for a fair introduction to evolutionary biology. Particularly "River out of Eden", which I enjoyed, and it is not a particularly long book.
I will get the ball set in motion with a simple enough question: What do you make of the creation (pseudo)scientific mantra touted by prominent creationsts like ppsimmons, and others? That Natural Selection is a "random" process? From here on we can discuss the various aspects of evolutionary principles, and why it is NOT random.

 

[Frenger]

Well I am glad I have joined this forum as evolution is my favourite topic too.

We could maybe collate the stronger points of this thread into an easy to understand PDF to post around. Just a thought.

Anyway.......

The "random" aspect of evolution is quite well understood, mutations in the gene pool occur when the DNA replicates itself through mitosis. Sometimes these "errors" can lead to a change in phenotype and a trait, for example neck length is changed.

In a changing environment traits such as a long neck might be an advantage, in which case, when the organism reproduces the genes for the long neck will be passed on again.

So, random mutations happen, but Natural Selection is force that drives these changes, there is nothing random about natural selection. Better adapted traits will survive, and less adapted traits will die out.

That's my basic understanding of it anyway.

The question that always gets me is "if we evolved from monkies, why are there still monkies?".

An easy one but it keeps us going. Also, if there is any mistakes in what I said or anything I missed (remember, it is just a basic account, I mean major details) then please add.

 

[CosmicJoghurt]

Are we, kids with no science education besides pre-highschool level general crooked and scientifically innacurate, vague ideas, who only know a bit about evolutionary theory and fact from Wikipedia and forum discussions with stubborn idiots, allowed in the discussion? I'd be delighted to take part...

 

[Dean]

Are we, kids with no science education besides pre-highschool level general crooked and scientifically innacurate, vague ideas, who only know a bit about evolutionary theory and fact from Wikipedia and forum discussions with stubborn idiots, allowed in the discussion? I'd be delighted to take part...

Yes, CJ (if you don't mind me calling you that). Happy to oblige! I'll try to at least get this off the ground ....

Evolution contains multiple random elements, but is by no means randomly driven. To be precise, there are many evolutionary processes. In fact, I was taught at the start of my degree that there were five evolutionary processes, as follows:

Mutation: Introduces new variation. Random. (A gene for black coat appears in a herd of otherwise brown cattle.)
Genetic drift: Changes in allele frequency by "random walk". Obviously also random. (The black coat gene confers neither an advantage or a disadvantage and may remain in the population or not purely because of chance.)
Migration: Flow of genes between populations. Random. (The black coat gene may be introduced from another herd of horses, all of them black - if that herd is bigger, the immigration of of black horses will likely be bigger than the emigration of brown horses.)
Recombination: Genetic recombination during meiosis results in reshuffling of genetic variation. Random. (Difficult to make an example of but imagine that all the horses in the brown herd had a white patch on their forehead, the gene for this being linked to the gene for brown or black. Then a black horse without a white patch immigrates. Its offspring may reshuffle genes so that brown is linked to no white patch.)
Natural selection: Changes in allele frequency due to difference in the fitness of phenotypes. NOT random. (For some reason black horses seem to be better at resisting a certain parasite than brown horses. The black gene has a fitness advantage and will spread through the population.)

Simple enough?

 

[tuxbox]

Evolution By Natural Selection -- A Discussion of The Basics

With the interest of a couple of individuals, such as WarK and theyounghistorian77 - along with (possibly) Hytegia - I open this thread to invite general discussion of the basics of Evolutionary Biology - anything and everything to do with modern evolutionary theory. This was also accentuated by the fact that evolution happens to be my favourite subject in the whole woooorld!

Hopefully, this could also offer a launch-pad so to speak, for anyone who is as of yet uncertain about the subject of evolution, to get a decent understanding of it.

Cool beans...

 

[Squawk]

Hmm, pedant here.

Better adapted traits will survive, and less adapted traits will die out.

A better way to phrase this would be to say that traits which confer an advantage survive with higher probability than those that don't. It's entirely possible for the more advantageous variation to go extinct, it's just less likely.

The question that always gets me is "if we evolved from monkies, why are there still monkies?"

This question is easy to counter once you understand the premise. That we evolved from monkies. The person making this claim usually wants the term monkies to refer to modern day species of ape, so for simplicities sake lets go with our nearest relative, the chimp.

We did not evolve from chimps anymore than chimps evolved from humans. Humans and chimps share a common ancestor, and at the point of speciation the ancestral species went extinct.

Great idea for a thread btw.

 

[Frenger]

Ha, sorry squawk, I really mis-wrote that end line, I meant as in "the question I always get which annoys me" rather than "the question that always stumps me".

Very interesting topic though, maybe we could talk avbout our evolutionary history and methods of following it ie mitochondrial DNA and the fossil record.

 

[Sparky]

We did not evolve from chimps anymore than chimps evolved from humans. Humans and chimps share a common ancestor, and at the point of speciation the ancestral species went extinct.

Is this actually what happened or is it a thought? I thought it more likely that the ancestral population would have split into two separate populations. Perhaps this could have occurred via migration of some of the original population far enough that genes between the (now) two populations were no longer shared. Then due to the differing pressures on the two populations, different traits were selected for and so on and so forth till we have what we have today.

I don't have any evidence for what I say (hence, if I'm wrong please say so) but it seems weird that "at the point of speciation the ancestral species went extinct." I guess this could maybe occur if the ancestral species was out-competed by the new species. Still I find it hard to believe a new species, differing only just enough so that sexual reproduction between the two populations cannot occur, would differ by enough that one could drive the other to extinction unless one is a proponent of punctuated equilibrium.

 

[Frenger]

We did not evolve from chimps anymore than chimps evolved from humans. Humans and chimps share a common ancestor, and at the point of speciation the ancestral species went extinct.

Is this actually what happened or is it a thought? I thought it more likely that the ancestral population would have split into two separate populations. Perhaps this could have occurred via migration of some of the original population far enough that genes between the (now) two populations were no longer shared. Then due to the differing pressures on the two populations, different traits were selected for and so on and so forth till we have what we have today.

I don't have any evidence for what I say (hence, if I'm wrong please say so) but it seems weird that "at the point of speciation the ancestral species went extinct." I guess this could maybe occur if the ancestral species was out-competed by the new species. Still I find it hard to believe a new species, differing only just enough so that sexual reproduction between the two populations cannot occur, would differ by enough that one could drive the other to extinction unless one is a proponent of punctuated equilibrium.

I think you have misunderstood an aspect of evolution here. Remember it is gradual, there is no "point of split" so to speak. All species are transitional and therefore they wouldn't neccessarily "drive the other species to extinction". They have just changed. We would have (most likely) split with our shared ancestor due to geographical reasons and went our seperate ways. One group went one way, and the other group went another both evolutionary and geographically speaking. This common ancestor wouldn't have gone extinct in the way you think, it just changed in two different directions.

I hope I understood your point and made sense in the answer.

 

[Sparky]

I think you have misunderstood an aspect of evolution here. Remember it is gradual, there is no "point of split" so to speak. All species are transitional and therefore they wouldn't neccessarily "drive the other species to extinction". They have just changed. We would have (most likely) split with our shared ancestor due to geographical reasons and went our seperate ways. One group went one way, and the other group went another both evolutionary and geographically speaking. This common ancestor wouldn't have gone extinct in the way you think, it just changed in two different directions.

I hope I understood your point and made sense in the answer.

Haha this is pretty much exactly what I was trying to say! I guess my explanation wasn't particularly good :?

 

[CosmicJoghurt]

Something that always stumps me (AFAIK this example is actually correct): let's say a male individual was born with a mutation that merged two chromosomes into one (not quite sure if that's very accurate, it's my general idea after watching a YT video or two regarding this example). How would this individual and female of the same species breed and have potential fertility? Isn't the genetic change.. too much?

I'll link the video I got this from when I find it, I'm pretty sure it's about humans and a common ancestor.

And, excuse me for the lack of half-decent terminology.

 

[Frenger]

I think you have misunderstood an aspect of evolution here. Remember it is gradual, there is no "point of split" so to speak. All species are transitional and therefore they wouldn't neccessarily "drive the other species to extinction". They have just changed. We would have (most likely) split with our shared ancestor due to geographical reasons and went our seperate ways. One group went one way, and the other group went another both evolutionary and geographically speaking. This common ancestor wouldn't have gone extinct in the way you think, it just changed in two different directions.

I hope I understood your point and made sense in the answer.

Haha this is pretty much exactly what I was trying to say! I guess my explanation wasn't particularly good :?

Ha, oops, sorry, I shall take a bit more care to understand before saying anything.

 

[Squawk]

Cosmicjogurt, if you go read my debate with micah you'll find I presented a paper on sheep which breed perfectly happily with different chromosome counts. A fusion is a big change, but there is nothing inherrant in a fusion to prevent breeding, or to detract from fitness.

Sparky, extinction in this sense does not mean extinction the way we might refer to, say, the dodo going extinct.

Lets say I have population A, all in one location, all interfertile. It's a species. Now, lets say we have a split in the population due to some event, earthquake say, resulting in geographic isolation, and refer to the two new populations as pop B and pop C.

Two distinct populations, but both are still the same species.

Over time they diverge genetically, such that eventually pop B and pop C are incompatible genetically. At that stage, pop B and pop C are both daugther species of pop A, and the original species is extinct. It is no longer possible to state that either pop B or C is species A in any rigorous way. Of course you can refer to the population which has experienced the least change as being more like the ancestral species if you want. But the original species is extinct due to the formation of two daugther species.

As an example, I propose to you that, at one stage in our evolutionary past, you could have referred to the mammal species. You can't do so now, it's extinct, because it has diverged into hundreds of sub-species, and is now classified much higher in taxonomy.

 

[devilsadvocate]

Something that always stumps me (AFAIK this example is actually correct): let's say a male individual was born with a mutation that merged two chromosomes into one (not quite sure if that's very accurate, it's my general idea after watching a YT video or two regarding this example). How would this individual and female of the same species breed and have potential fertility? Isn't the genetic change.. too much?

You might want to read this short article on Panda's Thumb by Dave Wisker that directly addresses the problem.

"The Rise of Human Chromosome 2: The Fertility Problem",

http://pandasthumb.org/archives/2009/02/the-rise-of-hum-1.html

 

[Dean]

[ ... ] The question that always gets me is "if we evolved from monkies, why are there still monkies?" [ ... ]

[ ... ] The person making this claim usually wants the term monkies to refer to modern day species of ape, so for simplicities sake lets go with our nearest relative, the chimp.

[ ... ] Humans and chimps share a common ancestor, and at the point of speciation the ancestral species went extinct. [ ... ]

Thank you. Duly noted, Squawk.

In encounters with creationists, assuming that they have an open mind, it may be advised to reference the fact that the web is chock-full of excellent resources that present the overwhelming evidence for evolution, clearly and concisely.

• * U.C. Berkeley's MofP clearinghouse -- Understanding Evolution
  
  
• * Evolutionary biologist Edward O. Wilson's brainchild, via his TED Award ... Encyclopedia of Life ... "Imagine an electronic page for each species of organism on Earth..." - Edward O. Wilson
  
  
• * PBS's Evolution ..."A journey into where we're from and where we're going"
  
  
• * The National Science Foundation's Special Report (interactive), Evolution of Evolution, 150 Years of Darwin's 'On the Origin of Species'

'Course, robust documentation of speciation events is fine, provided that these cases are broadly accessible and comprehensible to the sizeable population that now rejects Darwinian evolution in favor of creationism. If these cases are buried in technically specialized sources, the exercise of "broadcasting" them becomes analogous to looking for a needle in a haystack.

Also, documented cases of speciation will have a diminished explanatory force in the absence of a proper general context for understanding them.

 

[Dean]

@CosmicJoghurt
Ok. I guess Squawk was aiming his explanation at people who already had a strong grasp of the processes anyhow. Of course, when speaking of the five processes, this might become a little difficult... because basically you'll need an introduction to genetics to understand certain concepts. So, here's the processes again, and I'll try to define the technical words this time, for the benefit of CJ, since I love challenges, especially ones like these.


First of all, evolution these days is defined as a change in allele frequency. What is an allele? Well, I'm sure most of us are familiar with the basic setup of our genes. DNA is bundled into chromosomes, and specific genes correspond to specific parts of these chromosomes. Natural selection hinges on heredity and variation - the genes are what we can inherit, and so there obviously needs to be variation in the genes. For instance, look at the peas Mendel used - he had yellow and green ones. The yellow and green colours were determined by the same gene, but different alleles: an allele is a specific variant of a gene. If you have a population of peas where most of them are yellow, but there is a fitness advantage to being green, the green allele will increase in frequency, and evolution by natural selection has happened.

• Mutation: Introduces new variation. Random. (A gene for black coat appears in a herd of otherwise brown horses.)
• Genetic drift: Changes in allele frequency by "random walk". Obviously also random. (The black coat gene confers neither an advantage or a disadvantage and may remain in the population or not purely because of chance.)
• Migration: Flow of genes between populations. Random. (The black coat gene may be introduced from another herd of horses, all of them black - if that herd is bigger, the immigration of of black horses will likely be bigger than the emigration of brown horses.)
• Recombination: Genetic recombination during meiosis(*) results in reshuffling of genetic variation. Random. (Difficult to make an example of but imagine that all the horses in the brown herd had a white patch on their forehead, the gene for this being linked to the gene for brown or black. Then a black horse without a white patch immigrates. Its offspring may reshuffle genes so that brown is linked to no white patch.)
• Natural selection: Changes in allele frequency due to difference in the fitness of phenotypes(**). NOT random. (For some reason black horses seem to be better at resisting a certain parasite than brown horses. The black gene has a fitness advantage and will spread through the population.)
  • (*) Meiosis is the process by which we create gametes, that is, sex cells - eggs and sperm (did you know that this is the only real way we define male and female? a female of a species is the one producing large, nutrient-rich, immobile gametes, whereas the male is the one that produces small, nutrient-poor, motile ones). During meiosis, we copy our genome, and then divide it up into gametes. If you want I can go through the entire process in more detail but I don't think it's necessary for this. Genetic recombination happens in organisms like us that are diploid: we have two sets of chromosomes, one that we inherited from our mother and one from our father. These chromosomes would look more or less exactly like the ones we got from our parents, and hence like the ones they got from their<i></i> parents, if not for recombination. Basically, what happens is that we line up the chromosome from our father with the corresponding one from our mother, and then swap some of the alleles around! That way we end up with completely new versions of the chromosomes, creating more diversity among our offspring. (Faulty recombination can also lead to gene duplication or loss of genes, the more dramatic kind of mutations.)
    
    
  • (**) In biology, we speak of an organism's genotype and phenotype. The genotype is the complete genetic make-up of a particular organism - basically, the sequence of it genes. Which alleles it has in what combination. The phenotype, on the other hand, is the observable characteristics (apart from the DNA) of the organism. For instance, coat colour, or a disposition for violence, or the way a specific protein works.

In short, evolution is a stochastic process in that involves random elements (which as far as I know is the definition of stochastic; a process that involves random elements). But it's not an entirely random process).

Natural Selection on the other hand is an entirely nonrandom process, and is ONE of the mechanisms of evolution (defined as the change in frequency of alleles in a population).


While we're at it, here's the very simple and elegant explanation of natural selection, showing that it's pretty much inavoidable:

• 1. Individuals in a population are different from each other; there is varation. This is easily demonstrable, just go out and look at any population of, well, anything!
• 2. The variations are inheritable. This was a problem back in Darwin's time because we didn't know HOW. Now we have genetics, and so that problem is solved - inheritability of traits is again, often easily demonstrable.
• 3. In every generation, some individuals will have more offspring than others. Again, anyone who's bred any sort of pet will know that some individuals are more healthy and fertile than others.
• 4. The survival and reproduction of individuals - their fitness - is not random. The individuals which carry traits that are better for their survival and reproduction will survive better and reproduce more. Hence their genes will increase in frequency.

 

[Sparky]

Sparky, extinction in this sense does not mean extinction the way we might refer to, say, the dodo going extinct.

Lets say I have population A, all in one location, all interfertile. It's a species. Now, lets say we have a split in the population due to some event, earthquake say, resulting in geographic isolation, and refer to the two new populations as pop B and pop C.

Two distinct populations, but both are still the same species.

Over time they diverge genetically, such that eventually pop B and pop C are incompatible genetically. At that stage, pop B and pop C are both daugther species of pop A, and the original species is extinct. It is no longer possible to state that either pop B or C is species A in any rigorous way. Of course you can refer to the population which has experienced the least change as being more like the ancestral species if you want. But the original species is extinct due to the formation of two daugther species.

As an example, I propose to you that, at one stage in our evolutionary past, you could have referred to the mammal species. You can't do so now, it's extinct, because it has diverged into hundreds of sub-species, and is now classified much higher in taxonomy.

Cool. This makes a lot more sense - It's actually what I was trying to say I thought might be more likely to happen in my post

 

[Squawk]

I do have a bit of an issue, and it's one that I only reaslised recently. A consequence of exposing yourself to evolutionary research, argument, debate and discussion over a prolonged period of time is that you end up taking certain snippets of knowledge for granted. I realised this recently when discussing evolution with a friend, intelligent, but not clued up on the subject, and ended up regressing right back to basics. So, if I end up spouting stuff that sounds like shit, stop me.

Regarding that defintion of evolution dean, it's not strictly speaking complete. Changes in allele frequency are an observation of evolution, but are not evolution itself. Evolution is simply descent with modification in a reproducing population, which by necessity will lead to changes in allelic frequency simply through random chance.

That really is being a pedant though, and the allele thing is a good starting point (and one I've used often).

 

[CosmicJoghurt]

Dean, that was great! I already knew those genetic basics, but the rest was very well explained as well. It's alright if I keep coming with silly questions, right?