Re: Why does the mitochondrial evidence contradict the Multiregional hyp.

Great Question, Anna!

The multiregional (or candelabra) hypothesis, suggested by Milford 
Wolpoff, posits that populations of modern humans split off from common 
ancestors a long time ago- maybe 1 or 2 million years ago. These 
populations then evolved parallel to one another and interbred. 

You can find info on Wolpoff and his latest book here. 

Mitochondria, organelles that produce most of the ATP in eukaryotic cells, 
have their own DNA and reproduce within the host cell. Like chromosomal 
DNA, mitochondrial DNA (or mtDNA) slowly accumulates random changes. These 
changes can serve as a measure of time or evolutionary distances. 

How's that you say? In vertebrates, all mitochondria are maternal in 
origin- there is no sexual recombination of mtDNA, so changes in sequence 
occur less (compared to nuclear DNA) over time. (A cool illustration of 
this (thanks to Curtis and Barnes) is that you have 16 great-great-
grandparents, but all of your mitochondrial DNA comes from only one. As a 
consequence, mitochondrial linkages are easier to trace.)

Rebecca Cann & her colleagues at the University of California at Berkeley, 
took mtDNA of 147 individuals from 5 geographic populations- Africa, Asia, 
Europe, Australia, and New Guinea and compared patterns. They analyzed the 
data and concluded that:

1. There was a common ancestor (hence the term mitochondrial Eve) at the 
base of our 'evolutionary tree'. 

2. Using accepted mitochondrial mutation rates, she is estimated to live 
150,000 to 250,000 years ago. 

3. The population of African mtDNA was more variable, so they concluded 
that it had been around longer, and that Eve was from Africa.

4. Based on the variation of the non-African groups, the founder 
populations left Africa about 100,000 years ago.

5. There was no evidence of introductions of new mtDNA into the study's 
populations.

I found an article. in the 
Washington Post dated Friday, July 11, 1997; Page A01, by Staff Writer 
Curt Suplee. Here's an excerpt:

Wolpoff said that the researchers may have "jumped too soon to conclusions 
where there are actually several different ways of interpreting the data." 
If early human populations were "very small and isolated from one 
another," then gradually each would accumulate "different losses [in 
mitochondrial DNA] until they all came to look really different from 
each other because of the drift. Of course their last common ancestor 
would appear to be very far in the past." 

Because the mitochondrial clock ticks faster, it is more difficult to 
interpret events that transpired very long ago, and the arguments rage on!