A serious question about evolution. I need some really smart people to answer!?

http://www.msnbc.msn.com/id/9136200/ - 40 million nucleotide changes



http://www.answersingenesis.org/tj/v17/i鈥?/a>

up to 95% difference



Here are just a few simple sources that lead people to quote the percent difference between humans and chimps.

My questions are as follows. If humans and chimps are (I will use the conservative average) 98.5% similar and 1.5% dissimilar, what is the similarity and dissimilarity between both of these and their common ancestor from say 3 million years ago. Would it be half way in between? Was that common ancestor more similar to a human by 50% than a chimp is? I would suspect the answer is no. The common ancestor was not halfway to a human between a chimp and a human and then a split happened and the human has evolved equally away from the common ancestor as did the chimp. I would suspect the DNA of the common ancestor was probably the same amount as different as a chimp is from a human, or greater. I don't know if there is any studies to refute this or establish it, (There probably is no genome sequence comparisons that are able to be done on an early ancestor like this) So, I will use the 1.5% difference between the common ancestor and the human for my question.



This 1.5% accounts for 45,000,000 single nucleotide changes. The changes in nucleotides is fairly well understood and the rate is fairly well establised. Using that number, how was there enough time for a single nucleotide change to occur, that single change provide a selectable advantage (is that even possible), then that single change spread to enough of the population in order not to be swallowed back up it the pool of well functioning DNA sequences. (We realize that there is not really a life or death advantage between a chimp and a human as far as enviroment and diet. The percent of selectable advantage difference I think would be really low. (This single change could not account for a stark survival rate difference.) Then have more single point changes occur in benifitial areas in the DNA. Avoid and select out any that occured in the genes that negitivly effected the 10's of thousands of things in the body that that cannot be altered without death or negative effects occuring. (chemistry- molecular biology - needed organs, ect.) Have the random single point mutations occur in the correct spot and in the correct direction to bring the common ancestor 3 million years ago up to a human. Using the 45 million nucleotide changes and the 3 million years there would have to be 15 of these events every year for 3 million years. Is that possible?
A serious question about evolution. I need some really smart people to answer!?
An interesting analysis ... and I defer to the great answers already provided by emucompboy and Wise Duck.



I'lll just emphasize the two errors in your calculations.



First is the assumption that if humans and chimps show a 1.5% difference, that this means a 1.5% difference with the common ancestor. Instead, there is no reason to assume that chimps have not been evolving just as much as we have ... so emucompboy is correct that the correct number should be 0.75%.



Second is failing to differentiate between genetic DNA (DNA actually involved in coding genes) and (for lack of a better term) junk DNA, which does not code for genes and represents as much as 98% of our DNA. The 1.5% difference between humans and chimps ... or 0.75% between humans and the common ancestor ... refers to the *genetic DNA*, which represents only about 6 million base pairs ... so 0.75% of 6 million is about 45,000 base pairs difference. So over 5 million years, that's about 1 base-pair difference in genetic DNA every 111 years (if I did my math right). That is not hard for natural selection to explain.



Now if you want to use the full genome of 3 billion base-pairs, instead of just genetic DNA, then the numbers are much larger ... but, then natural selection is not acting on junk DNA. I.e. changes to junk DNA, since they do not code for anything that affects the owner one way or another, are neither beneficial nor harmful ... they are neutral. As such, they do not have to be selected for, or survive the culling of being selected against ... they just appear due to random mutations, and spread into the population by genetic drift. So natural selection doesn't have to explain them.
A serious question about evolution. I need some really smart people to answer!?
I think that the common ancestor was more than 3 million years ago. You are make an assumption on that figure. In any case there would not likely be 15 changes per year, but a large number in certain years due to mutations or other factors.
%26gt; I will use the 1.5% difference between the common ancestor and the human for my question.



You should assume that chimps have evolved equally away from the common ancestor, and thus use only 0.75%. LOL. It's very speculative, but I'll play along.



%26gt; then that single change spread to enough of the population in order not to be swallowed back up it the pool of well functioning DNA sequences.



Small population(s). At most times before agriculture, the human species comprised scattered small populations. We also seem to have had genetic bottlenecks, in which the total number of living humans was small.



%26gt; stark survival rate difference

It's not %26quot;survival of the fittest.%26quot; It's %26quot;reproduction of those fit enough to reproduce.%26quot;



%26gt; 3 million years

Nope. Our common ancestor with chimps was about five million years ago.



So let's redo your math:

0.75% over 5 million years. 3 billion * .0075 = 22,500,000 changes. That's 4.5 changes per year. Seem more reasonable? But -- most of those changes are neutral anyway.



So, let's look at the non-neutral changes.



Instead, look at it from another standpoint.

We have 25,000 genes. Let's say that 0.75% of them have changed since our last common ancestor with chimps. That's only 188 genes having changed since our last common ancestor with chimps in five million years. That sounds pretty reasonable, doesn't it?




The 98.5% refers to coding sequences.

95% is total genome.



There are around 175 mutations per generation of humans. It is likely the number is close to that of chimpanzees and our ancestor.



Our common ancestor with chimps was around 6 million years ago. If we assume a generation time of about 18 years (probably a high estimate), we get a total of 1050000000 mutations.



This number is over 400 times larger than the total nucleotide difference between chimpanzees and humans, even if we assume maximal difference.



Clearly the number of possible changes dwarfs those that were fixed in our genome.



So, how did they spread? Single nucleotide changes can result in a beneficial phenotype. This has been confirmed time and time again in the lab. Any benefical mutation will spread in a population.



If the mutation is a same-sense or in a non-coding region it is probably irrelevant, and its fixation depends on genetics drift. The population of human ancestors was rather small, so there was a non-trivial amount of drift occurring. Find a population geneticist to explain the equations that determine this.



More importantly, there is a lot more to mutations than single nucleotide polymorphism. Since the divergence of humans and chimps, a chromosomal fusion, several inversions, duplications, viral infections, and other larger scale genomic events have occurred.