Archive | October, 2012

Discussion of mitochondrial Eve in relation to Human Evolution at Secular Cafe

1 Oct

So what is big deal about Mitochondrial Eve? Why is it relevant to the consideration of human evolution from 2 million years ago until today expecially in South and East Asia?

Cath B at Secular Cafe replied: The study of mitochondrial DNA (mDNA) is an important tool in our quest to understand the routes and time-scales involved as the ancestors of modern humans colonised different parts of the planet as well as the extent to which this involved assimilation with and/or or replacement of earlier populations.

The knowledge we have gleaned and continue to glean, from mDNA and other studies provides convincing evidence that descendants of Mitochondrial Eve and associated contemporaries then living (current evidence suggests) in East Africa were the predominant or only ancestors of all people in all parts of the world living today.

I then asked concerning the human mitochondrial molecualar clock (http://en.wikipedia.org/wiki/Human_mitochondrial_molecular_clock): I have no problem with accepting the use of the word ‘predominant’, but am not sure that mitochondrial Eve can be said to be the only ancestor of all people (male and female) living in all parts of the world today. I need genetic evidence to conclusively prove that this is the case. What does it say about the Han Chinese? In particular I am concerned that the descendents of the earlier migration of Homo erectus from Africa 1.5 million years ago from whom the recent hobbits (Homo floresiensis) arose in Indonesia are said to have all gone extinct. Also I do not know what the species name of mitochondrial Eve is supposed to have been: Homo ergaster, homo sapiens, homo erectus, H. rhodesiensis/H.heidelbergensis: if it was the latter how did it differ from the earlier species?

Also, I have concerns on the methodology of mitochondrial Eve. To be able to determine the natural mutation rates as you describe reliably, scientists would have had to examine the mtDNA of at least 10 generations of female human beings in a single family, and then replicate this kind of observations 20 times plus. Do you have a reference or a link/report on the results of such a study?

Also do you know if there is a published report on the derived mtDNA sequence of mitochondrial Eve?

Comment: I posted essentially the same questions at Secular Cafe as I had done at Talk Rational.org, but  posters/moderators here indicated that I should do my own homework instead: http://secularcafe.org/showthread.php?p=408011#post408011. I prefer to develop knowledge through interactional sharing of opinions. Accordingly, I would welcome any posts on the subject directly at this blogsite so that the analysis of the science of human evolution may be taken forward one step at a time in a way that ordinary people can comprehend the story and posters and commentators receive due credit for their contributions.

Discussion of mitochondrial Eve in relation to Homo ergaster at Talk Rational.org

1 Oct

In view of the lack of comments in this blog on the topic of mitochondrial Eve and its implications and relationship to Homo ergaster, I took my question to Talk Rational.org for the views of experts who post there. The discussions may be followed in the following link:http://www.talkrational.org/showthread.php?t=52309 (MRCA – most recent common ancestor).

The essential posted words were from Steviepinhead as follows:DEPENDING ON WHICH KIND OF DNA WE’RE TALKING ABOUT, we’ll have a different set of ancestors. The MRCA of all living humans has to comprehend the multiple lines of inheritance involved with the nuclear (chromosomal) DNA — with the exception of the Y in the case of males. So that’s going to necessarily run back to a different person than the single, matrilineal, all-female, mother-to-daughter-only line of inheritance for mtDNA. … For these reasons, mtDNA “Eve” is just that, the MRCA of all the mtDNA borne by all living humans. She’s NOT the MRCA of all humans (in the sense of tracing the chromosomal DNA back through multiple criss-crossing lines of inheritance). She’s not even necessarily, for the same reason, the MRCA of all living human females. WHY NOT? Because human females have more kinds of DNA — and more lines of inheritance — than JUST their mtDNA. The only kind of DNA of which mtDNA “Eve” is the MRCA is the (remnant) mitochondrial DNA. We could go through the same kind of analysis for Y-chromosome “Adam” and get similar results.

Comments:

(1) It seems to me that the only sound way of determining MRC (human)A of all human beings alive today from genetic analysis would be to examine the entire nuclear (chromosomal) DNA for sequence patterns; but that due to considerable size and variability plus mutational changes between generations it is not possible for modellers to do this kind of computational prediction. So they choose the easier option of mtDNA and Y-chromosome DNA for modelling purposes. The entire nuclear genome analysis might take us back to a Homo ergaster as the source of all humans alive today. However, this kind of study is near impossible to do because of changes introduced by recombination; further DaveGodfrey suggests that the MRCA for nuclear genes is in fact likely to have been much more recent than Mitochondrial Eve or Y-Chromosome Adam citing the following report: http://tedlab.mit.edu/~dr/Papers/Rohde-MRCA-two.pdf. I do not follow this logic and the topic is compounded by other considerations.

(2) To be able to determine the natural mutation rates as you describe reliably, scientists would have had to examine the mtDNA of at least 10 generations of human beings in a single family, and then replicate this kind of observations 20 times plus. And this suggestion would still only amount to a preliminary look-see investigation with more detailed studies needed. There is no other way to get at the facts on mutations, mitochondrial or nuclear. The entire concept of randomness in the nature and frequencies of DNA mutations will come under scrutiny. This may show that there are no consistent natural mutation rates on any kind of mutation on which to base any analyses and prediction of Eve. Specifically, how many different patterns of mtDNA sequences have scientists recognised in total in the current world populations of females and males, and how was the probability of each pattern in the total world population estimated? Secondly, what are the total number of different kinds of mutations possible in the mtDNA and how will anyone know for certain that these figures were the same in all previous generation of humans as they are in today’s generation. Thirdly, how can anyone estimate the rate at which these generational mutations took place without conducting studies on the actual DNA of humans over the generations?

Until the computational methodology is validated by hard scientific evidence of this nature or indeed on the theoretical facts upon which the prediction of mutation rates are actually based, the finding of a mitochondrial Eve at 200,000 years ago can only be regarded as speculative. In other words, there has to be sound basis for probabalistic computations to derive ancestry in genetic science. I would like to see evidence that the researchers have addressed these issues soundly.