Mitochondria and the biological "Eve"

Mitochondria- Shaped like oval organelles and made of a double membrane. The outer membrane creates the oval shape, while the inner membrane is wrinkled, creating folds. The organelles are about a half-micrometer in diameter and roughly two to five micrometers in length.
Cristea- These are the inner folds made by the second membrane, creating more surface area.
Mitochondria play a vital role in the functioning of a living cell. They are responsible for much of the biochemical processes that break down nutrients, whereby producing energy used by the entire cell. Much of this takes place on the cristae.

At one time, many cells existed without mitochondria. Although they were funtioning cells, they could not perform the higher functions, as they do presently. Most cell biologists believe that at one time, mitochondria were free-living organisms and they eventually, through forms of evolution, formed a symbiotic relationship with other larger cells. The larger cells were able to provide the mitochondria with the nutrients they needed and, in turn, the mitochondria could extract energy more efficiently than the larger cells. They could provide the large cells with the special molecule, adenosine triphosphate (ATP); mitovhondria are often referred to as "the powerhouses of the cell" because of this boichemistry. The mutual gains produced by such a relationship, is what is meant by a symbiosis.

Evidence accumulated in the 1960's, shows that mitochondria posses their own DNA. It is also known that the DNA mitochondrial information of cells is passed through the maternal side. Which is one reason for the fascination with looking for the biological "Eve", i.e. the first human woman.

The reason that our mitochondrial ancestor is an Eve , rather than an Adam, is based on reproductive physiology. In addition to the egg, the sperm also have mitochondria, except their energy is responsible for motility, therefore none of their mitochondria is contributed during fertilization. In contrast to the ever-shuffling behavior of our genes from nuclei, mitochondrial genes remain intact and unmixed, whereby creating an unbroken chain leading back to the mythical Eve.

Much research has been done to attemp to estimate the approximate area and time frame that the first woman would have lived in. During the mid 1980's an extentive project was undertaken by Allen Wilson, Rebecca Cann, and Mark Stoneking. First they analyzed the mutation rate of mitochondria and found it to be a rate of 2-4% every million years. Their next step was to analyze how DNA differs amoung different populations of Homo sapiens. The team collected mitochondrial DNA information on many women from five geographic areas: Europe, Asia, Africa, New Guinea, and Australia. The information from most of the areas were relatively similar, meaning that they had only recently diverged from eachother; although the information from the women from Africa were significanly different, implying that humans have lived far longer in Africa. Using the mutation rate already calculated, the team concluded that she must have existed some time between 140,000 to 280,000 years ago.

This hypothesis raises many questions as to which present theories are correct about the origin of our species. Their are two opposing theories: the "out of Africa" theory, that this finding supports, that Homo sapiens evolved as one species in Africa and dominated all of the other human-like species around the world. The other theory is that Homo sapiens evolved through the interbreeding of many species.

Also their are many criticisms of this particular study, in the way they analyzed the mitochondrial evidence, and also the samples of women they chose to use. Further evidence has been found to both refute and to support this theory; DNA fingerprinting has shown the greatest diversity in the African population, and yet skulls have been found in China that date as far back as 350,000 years. Therefore, at this writing, the controversy continues.

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