First of all, has there actually been enough time for evolution to be the explanation? Micro-evolution can be very quick-varying breeds of dog for example, but to evolve from a sea creature to a land animal is an altogether different order of change.
Secondly, whereas living things tend to decay, evolution 'gets better' instead. I suppose I’m talking about the components of life, DNA etc., not so much the length of limbs, or some other evolutionary advantage.
I’m sure Dawkins must mention it somewhere, (I’ve been about to start The Blind Watchmaker for a while!) but I’d quite like to know now!
Also Googling 'evolution' brings up a lot of places including, of course, Wikipedia and the following - http://www.pbs.org/evolution.
Well, 3.8 billion years seems like a hell of a long time to me, but I suppose you're thinking of the arguments of people like John Baumgardner ('Not long enough for evolution'). I think a response to that would involve a thorough, step-by-step analysis. Maybe others here would be better equipped to tackle it. But in the meantime, if I find a counterargument, I'll pass it on.Nick wrote:First of all, has there actually been enough time for evolution to be the explanation?
Fortunately, though, there are transitional fossils, like Tiktaalik and Ambulocetus, that make the idea of sea-to-land and land-to-sea evolution easier to imagine, even though many creationists deny that they exist.Nick wrote:Micro-evolution can be very quick-varying breeds of dog for example, but to evolve from a sea creature to a land animal is an altogether different order of change.
I'm not quite sure what the question is here. Is there an assumption that evolution should echo the lives of living things, and, if so, why? In any case, there are parallels between the development (and decay, and death) of living things and the development (and decay, and death) of species. Even though Haeckel's recapitulation theory (ontogeny recapitulates phylogeny) is now discredited, as the Creationists love to point out. It might be worth looking at the Eco-Devo section of the University of California at Berkeley site, Understanding Evolution. Then again, it might not.Nick wrote:Secondly, whereas living things tend to decay, evolution 'gets better' instead. I suppose I’m talking about the components of life, DNA etc., not so much the length of limbs, or some other evolutionary advantage.
Hope you get a better reply soon!
Macro evolution can be very quick too, after mass extictions there are usually explosions in the numbers of new species. Bear in mind also the distiction between microevolution and macroevolution is entirely artificial, it has no basis in reality.Nick wrote:First of all, has there actually been enough time for evolution to be the explanation? Micro-evolution can be very quick-varying breeds of dog for example, but to evolve from a sea creature to a land animal is an altogether different order of change.
Not sure what you are meaning here. DNA does not necessarily get "better" ther is a lot of junk DNA in our genomes, things like dud viral DNA and non functioning genes.Nick wrote:Secondly, whereas living things tend to decay, evolution 'gets better' instead. I suppose I’m talking about the components of life, DNA etc., not so much the length of limbs, or some other evolutionary advantage.
Another site you could try is this one:
It's where I found this definition of evolution.
"In the broadest sense, evolution is merely change, and so is all-pervasive; galaxies, languages, and political systems all evolve. Biological evolution ... is change in the properties of populations of organisms that transcend the lifetime of a single individual. The ontogeny of an individual is not considered evolution; individual organisms do not evolve. The changes in populations that are considered evolutionary are those that are inheritable via the genetic material from one generation to the next. Biological evolution may be slight or substantial; it embraces everything from slight changes in the proportion of different alleles within a population (such as those determining blood types) to the successive alterations that led from the earliest protoorganism to snails, bees, giraffes, and dandelions."
- Douglas J. Futuyma in Evolutionary Biology, Sinauer Associates 1986
I like it because it differentiates between the concept of evolution and the theory of evolution. The concept of evolution can be applied to many things as the quote states, but the theory of evolution only applies to biological evolution.
On the subject of transitional fossils it is worth remembering that evolution is a constant process, it does not stop. Therfore every fossil is a transitional fossil, every species is a trasitional species.
It also looks as if I've got to explain my bad science. My excuse is that I never did any biology at school (cutting up dead mice didn't appeal) but excuses may get you off the hook, but not where you want to go.
As I understand it, ageing occurs because of the inability of cells to reproduce themselves exactly. A bit like a photocopy of a photocopy of a photocopy. This seems logical to me, and what we see in practice.
How is it then, that when cells reproduce from one generation to another, that this degeneration does not take place? That the photocopy becomes not only as good as new, but sometimes better? I accept there may be 'junk' in DNA, but I like to think I am 'better than' my most ancient ancestors. (Even if I do look like the missing link.)
Cells are very very good at reproducing themselves very accurately, there are whole suites of enzymes which maintain, fix and correct DNA. Error rates in DNA is generally 1 in 1,000,000 to 100,000,000 and the vast majority of errors are totally harmless. In Eukaryotes ther is more non-coding DNA (does not code for a protein) than coding DNA (codes for a protein) the reason for this is unkown but there are a number of theories the most plausible of them for me is that all that much of the non coding DNA is structual DNA, it is there to support and possibly protect the coding regions of DNA.Nick wrote:As I understand it, ageing occurs because of the inability of cells to reproduce themselves exactly. A bit like a photocopy of a photocopy of a photocopy. This seems logical to me, and what we see in practice.
Aging is another of those biological processes which is poorly understood.
Better happens when one of the rare mutations gives an advantage. For example Syckle cell anaemia; there is one base pair difference between a normal beta haemoglobin gene and a syckle cell beta haemoglobin gene (there are a LOT of base pairs in the beta haemoglobin gene). But if you have one copy of the syckle cell beta haemoglobin gene and one normal beta haemoglobin gene you will have a significant improvement in your chances of surviving malaria. If you have 2 syckle cell beta haemoglibin genes you have syckle cell anaemia and you will die young.Nick wrote:How is it then, that when cells reproduce from one generation to another, that this degeneration does not take place? That the photocopy becomes not only as good as new, but sometimes better? I accept there may be 'junk' in DNA, but I like to think I am 'better than' my most ancient ancestors. (Even if I do look like the missing link.)
A mutation can be good, bad, neutral or both good and bad. The most common is a neutral mutation, it has no effect at all. A lot of change from one generation to the next comes from reproduction. Firstly from who gets to reproduce and secondly form the independant assortment of genes during meiosis. (Independant assortment info)
The other thing to remember is that in your body you have millions of cells if one of them mutates in such a way as it cannot survive it will die and be replaced.
Finally (For this post anyway) Remember that this is the basics, in reality it is much more complicated. Not all genetic information is in the DNA sequence, the DNA sequence is "annotated".
You should remember that simple organisms can reproduce every few minutes, and even complex mammals like rats can have a litter every few weeks. This can significantly speed up the mutation/selection process. When we get to humans the mutation/selection rate can be as low as once per couple of decades.First of all, has there actually been enough time for evolution to be the explanation?
We have to start with 3.5 X 10 to the ninth years. That times the number of seconds per year (365.2401 X 24 X 3600). Then the number of organisms on earth at any given moment. It started out as very few, but with whole oceans of nutrients, they procreated rapidly. I'll just take a guess and say there are probably a hundred trillion (10 to the 14th) organisms at any moment since shortly after the beginning of life.
When we consider that the earth is constantly being bombarded with large amounts of high energy radiation (cosmic to UV) that cause chemical bonds to break or join, it means that trillions of cell changes are occuring every day and have been doing so for the whole 3.5 billion years. Even if 99% are meaningless or lethal, 99% of that last percent are damaging mutations, that still means a very large number of positive tiny mutations happening all the time.
By positive I mean that they allow the organism to have a slight advantage in survival or procreation under the environmental contitions that obtain at the time. The sum of all these is also a huge number, and easily enough to account for all of the various micro-characteristics that go to make the characteristics in every organism that has existed.
If you're wrong, call me ... I'll have one for you!
Critical Thinking - http://www.skepdic.com/refuge/ctlessons.html
It's controversial, though, whether "species" are visible to selective forces. What does "advantageous to the species" mean from a gene-level view?Occam wrote:True. It's really annoying that so many things that are advantageous to the species are disadvantageous to the individual.
So, "advantageous to the species" probably could be stated more precisely as "advantageous to the lifeline".
I'm not certain of the meaning of your reference to "from a gene-levelview."
http://www.youtube.com/view_play_list?p ... F1BB7DFCD4
A lot of the other videos by ExtantDodo are interesting especially if you are concerned about the arguments made by creationists and a few quacks.
Well said!Occam wrote:You raise a good point in that any species at a given point in time is merely a part of the life line that started at the inception of life and is ongoing.
"Species" are a human construct based around historical classification. Aristotle first started using "genus" and "species" for categorising things and two hundred and fifty years ago Carolus Linnaeus suggested using these terms in a very specific (excuse the pun) way - giving us the binomial nomenclature for organisms that is still in use today.
Most people still hold on to the historical concept of biological species, but evolutionary theory allows us to consider organisms in a temporal context. This way of considering organisms provides us with more difficult criteria for classification, but it also provides us with explanations for observed complications to species concepts, for example reproductive overlap between apparently distinct but related "species" (Google "ring species" and you'll get some examples). Of course we need a contemporary classification to be able to work in biology, but it is important that we keep in mind that what we call modern "species" are actually just a temporal sample of a genetic lineage that is characterised by gene flow restricted within the population at that particular time.
In short, a "species" is a 3D representation of 4D genetic flow.
Is that not right then?
In reality the morphological species concept is the most commonly used and most practical method of identifying species (in biology and palaeontology), however, this is based on appearance and shared derived features rather than reproductive ability.
To be honest, species concepts are a can o' worms!
Thats one of the requirements used to define different species and when speciation has occured.Beki wrote:I thought that something became a different 'species' when the genetic code had diversified enough that any offspring were infertile. You know, like horses and donkeys mating to produce sterile mules.
Is that not right then?
However there are 2 buts.
It's not that simple.
Species are an entirely artifical concept.