The Theory Of Evolution and Natural Selection

UU

Hi all!

I'm studying Biology for the Leaving Cert. and I love it! It is so interesting, especially Genetics. I was studying Darwin's Theory of Evolution which I accept. I was discussing it on the Christianity forum in that long thread they have on Creationism vs Evolutionism, etc. I found it really annoying because the people wouldn't listen to a word I was saying and were saying that any proof I gave for Evolution was false and that we came from mud and are a result of incest! Also, they think that the Earth is 12,000 years old compared to over 4.6 billion years old!

It would be better to discuss it here with people who actually know what they're talking about as opposed to the usual "You said we came from apes" when we came from a Common Ancestor.

Anyway, did eukaryotic cells evolve from prokaryotic cells?

Faith

In a word, yes.

The evidence suggests that eukaryotes appeared around 2 billion years ago (compared with about 3.8 billion years for prokaryotes). There is little direct evidence of how they evolved, but this is thought to have been by fusion of one or more prokaryotic cells, perhaps the engulfment of one cell by another. The engulfed cell might live as an endosymbiont but, over time, lose the ability to live independently, and progressively lose some of its genome (or the genes might be incorporated into the host DNA). This is known as the endosymbiotic theory.

Creationists are crazy, everyone knows that!

5uspect

they're a crazy bunch alright

I'm reading Richard Dawkins "The Blind Watchmaker" at the moment. This is a book thats probably more relavent today than ever with the likes of Intelligent Design and the Discovery Institute making a mockery of science.

Unfortunately I'm not a biologist so I can't offer any information about your cell question. I'm an engineering PhD student and the research institute I'n studying in is currently working on cancer dianogistics so there's lots of merging with engineering and biology.

Biology is a really exciting place to study right now, I hope you keep up your interest and continue to study it.

Panserborn

UU wrote:

Anyway, did eukaryotic cells evolve from prokaryotic cells?

Interestingly, the mitochondria and chloroplasts that are in in euk cells are ancestors of prok cells. They still have their own DNA and replicate it (and themselves) independently of the host cell. Kinda cool in a wierd way. Probably arose as very early euk cells had no way of generating energy (so were technically not really cells at all) but the archea prok cells could and a symbosis emerged. Prok cells generated the energy, the host euk cells generated the food.

Let the creationists eat that!

UU

That's all quite interesting. Unfortunately in the Biology course, we don't have the opportunity to go into much detail in Evolution and Natural Selection. At least I'm not denied it like in the Bible Belt in the USA! :rolleyes:

Is it true also that the amino acids sequences in human blood is nearly identical to that of chimpanzees. I believe it is the cytochrome c protein?

On the Creationist thread, they started saying that any fossils of prehistoric homo sapeins were actually just apes but of course I didn't believe them. I heard there have been many finding in China. I found this website: Cool Website on Human Evolution. Take a look!

Faith

UU wrote:

Is it true also that the amino acids sequences in human blood is nearly identical to that of chimpanzees.

I don't know too much about this, but it's believed that we share up to 98% of our DNA with them. You can read more here:

http://www.newscientist.com/article.ns?id=dn2160

DrIndy

Faith wrote:

I don't know too much about this, but it's believed that we share up to 98% of our DNA with them. You can read more here:

http://www.newscientist.com/article.ns?id=dn2160

If we share 98% of DNA, then there must be some identical proteins. It is interesting that small amounts of DNA changes can make substantial differences in certain areas of development.

UU

Actually here are some interesting facts from my Biology book:

Compared to human cytochrome c protein which has 104 amino acids:
- Chimpanzees: Their entire sequence is identical (as is their haemoglobin)
- Rhesus Monkeys: Differs by 1 amino acid
- Chickens: Differs by 18 amino acids
- Turtles: Differs by 19 amino acids
- Yeasts: Differs by 56 amino acids

Apparantly the last ancestor humans and yeasts shared lived many hundreds of millions of years ago. However, more than 90% of their proteins and genes have not changed.

Hendrixcat

Hey UU,

Check out Dawkin's book The Ancestor's Tale. The hard back copy has very cool diagrams and schematics outlining the progression of species that has led to us. The importnat thing to take away from any of these books on evolution is that evolution has no direction as such. We might like to soothe our egos and believe that we are the pinnacle of evolution but that is a false conclusion to make. If anything, we will see our evolution take off at a phenomonal rate in the future due to the powerful methods of gene manipulation we have at our hands.

The Intelligent Design promoters (the modern term for Creationism) are a cunning group who's ideas have been rejected many times over the last few decades and each time they were shot down they have re grouped and returned with a new way of putting their silly beliefs to the public. ID is their latest attempt and thankfully it was tossed out of the school curriculum recently in Pennsylvania. One of their most powerful arguments was the pseudo-scientific theory of 'Irriducible Complexity'. This states that many complex biological mechanism such as the blood clotting cascade and the human eye cannot function even if only one of the many many pieces are missing. Therefore how could they have developed slowly over time? They believe that they must have been created all at once. However somebody then discovered that the clotting casacde of some whales is missing a factor or two but still seems to work just fine.....

Dawkins has other really cool books. If you haven't read 'Unweaving the Rainbow' yet give it a go. It helps a great deal with critical thinking and banishing superstition.

Faith

UU, are you thinking of studying biology after the leaving? I'd stongly recommend the course I'm doing if your interests lie in genetics and evolution because it focuses a lot of them, particularly in first year. And the lectures make fun of creationists a lot .

Have you applied to UCAS?

Hendrixcat

Regarding the conservation of protein sequence and therefore gene sequence between species; the most significant one for me is the sequence of histones, which are the proteins that DNA winds itself around in order to make chromosomes. These sequences are conserved to a high degree throughout every species and phylum right down to single celled organisms. It is a very compelling argument that we all descended from a single organsim a few billion years ago.

UU

Hi all,

Hendrixcat, thanks for your info. I'll take a read of some of Dawkin's books. I have heard they're all quite fascinating. About Intelligent Design? It isn't actually the same as Creationism from what I've heard but actually a stupid and weak attempt to combine both Evolution and Genesis.

Also when I was on the Creationist thread a poster said that Evolutionists say that we evolved from slime. I questioned how we came from mud! (lol) Then there are those who think that all Evolutionists are atheists yet I believe in God. Sure Darwin was actually going to become a clergyman and Gregor Mendel, who is regarded as the father of Genetics, was a Catholic monk.


Hi Faith. I'm actually going to study foreign languages in college (French and Spanish) but Genetics would be a second choice if languages didn't work out for me. I do have a keen interest in Biology and hope to retain it as a lifelong passion. I watch many documentaries, I am interested also in alternative medicine especially aromatherapy and read some publications also.

Another question. Did humans evolve into different races like Caucasian (White), Negroid (Black), Asian, etc. due to different climate, activity? Does that mean that there was one race evolved into others or the early humans spread around the globe and just evolved? Or did humans originate from one place on the globe?

GuanYin

DrIndy wrote:

If we share 98% of DNA, then there must be some identical proteins. It is interesting that small amounts of DNA changes can make substantial differences in certain areas of development.

Argh. This is a commonly mis-portrayed issue.

Considering the DNA conservation among species (common proteins for cell structure among mammals, enzymes that are widespread among species etc etc) and the amount of junk DNA in any given genome, the amount if similar DNA between any two organisms doesn't tell you much.

What is important is the differences - in other words, the 2% DNA that distinguishes chimps from humans tells us far more than the 98% that is similar.

Theoretically a creature could have 99% DNA homology to humans and be missing a gene that encodes a cell membrane protein or some regulator of cell division which would result in it being unable to maintain humanoid form.

Hendrixcat

The significance of the small percentage difference between various species is indeed important. But any attempt to trace back the lineage is going to depend upon conservation of gene sequences and how these have altered over time. The study of the 'molecular clock' can give us an idea of how long ago and to what extent organisms diverged. Also the similarity between the function parts of a genome also outines the importance that a particular protein or enzyme plays in bio processes. The histone is an example of a very important protein that is almost identical across all species.

DrIndy

UU wrote:

Another question. Did humans evolve into different races like Caucasian (White), Negroid (Black), Asian, etc. due to different climate, activity? Does that mean that there was one race evolved into others or the early humans spread around the globe and just evolved? Or did humans originate from one place on the globe?

It seems that by tracing mitochondrial DNA (which is conserved in the mitochondria and not affected in normal reproduction and is transferred by the maternal line) that all non-negroid races are derived from the same tribe and indeed the same woman who is believed to live somewhere in ethiopia and after the ice age moved northwards, eventuall spreading to europe, india and the far east and thence to australia and america.

Racial differences are smaller than the would appear. Certain distinct racial groups can also be traced by the language groupings such as indo-european which encompasses europe and india/pakistan including iran, arab/jewish, finnougric, turkmen, far east, aborigine/pacific island, america.

There are other distinct groups such as Basque and in southern india.

The single greatest thing is that all non-africans have one, female ancestor.

UU

Wow, that's really interesting DrIndy!

Ha! I knew women coming from the spare rib of a man was stupid! The power of the woman ancestor!

Also, are humans and other animals still evolving at present? Do you think that homo-sapiens might evolve again or is there an actual hault to evolution?

Panserborn

UU wrote:

Also, are humans and other animals still evolving at present? Do you think that homo-sapiens might evolve again or is there an actual hault to evolution?

Yup, humans are not the "final product" that evolution was striving to arrive at. We are at the current end of one branch of evolution and in time it will continue to change. Point to rem though is that evolution is a very VERY gradual process. In terms of the evolution of higher mammals, we will not notice it and the smallest changes can take 1000s of years. There is still controversey as to when out own H.sapien species officially arrived.

Some biologists argue that as we get more and more complex, evolution slows but never stops. There is some validity to this as we gather more and more non-coding DNA (the media call it "junk DNA") that can act as a mutation sink where mutations can occur that will not change any phenotype. Also, the "genetic wobble" minimises the effect of mutation on the species.

Take home message, evolution will never stop. Biology only makes sense in light of evolution.