|
|
|
Ancestry: The mother of all mothers
Whenever archaeologists try to trace the beginnings of human beings, they focus on the continent of Africa. However, the origins of early man have not been established positively.
The savannah grasslands of South and East Africa are an anthropological treasure trove for ancient fossils. This is where the oldest known human fossils were found.
The Olduvia Gorge is where archaeologist Louis Leaky, and his wife, Mary Leaky, discovered the partial remains of a hominid zinjanthropus that, being 1.75 million years old, remains the best archaeological evidence that Africa is the starting point of all civilizations. It is believed that all humans evolved from this earliest human.
Holy books, as source material, offer explanations concerning the roles played by Africans as part of a cultural and spiritual diaspora. Both the Bible and the Holy Quran state that the first man, Adam, was fashioned from dust or black mud. The first woman, Eve, was created from the ribs of Adam.
Because ancient DNA molecules are so few and fragmented, and preserved soft tissues so rare, scientists had little hope of finding and analysing them. But two breakthroughs have now made this possible.
The three major religions — namely Judaism, Christianity and Islam — originated in Africa. Africans spread their genes knowingly or unknowingly, intentionally or unintentionally, across the Indian Ocean to Pakistan and India, and across the Atlantic to the West and beyond.
Books are replete with multiple ways in which animals and plants spread their DNA (deoxyribonucleic acid) around the world. If animals and plants may use whatever means necessary, why can’t humans?
Slavery is said to have been used, as a vector, to spread African genes across the world. If it were not for slavery, would the African gene be as common across the world as it is today?
The name “Africa” is actually a misnomer, used by almost everyone today. This name derived from the Greek word “Aprica” — meaning “land of the Sun”.
This land was a massive continent, which had many names. The phrase “Akebu-lan” — “Mother of Mankind” or “Garden of Eden” — was used by the Moors, Nubians, Numidians, Khart-Haddans and Ethiopians. In 200 BC, historian Eratosthenes referred to Africa and present-day Libya as Libya Theriodes.
From the Ethiopian region, humankind ventured out to the other parts of the world. The first move was towards northeast Africa, then into Asia and Europe.
DNA can be used to understand the evolution of modern humans, trace the migration of people, identify individuals, and determine the origins of domestic plants and animals. DNA analysis, as one scholar put it, is the greatest archaeological excavation of all time.
Because ancient DNA molecules are normally so few and fragmented, and preserved soft tissues so rare, scientists had little hope of finding and analysing them. But two breakthroughs have made this possible: the polymerase chain reaction (PCR) — a method for copying any fragment of DNA — and the successful recovery of DNA from preserved hard tissues, bones and teeth, that are durable and relatively abundant.
The tracking of Mitochondria DNA — a special type of DNA which comes only from the mitochondria of the mother’s cell — proves that the first humans were from Africa. The African diaspora went full circle, from Africa to Europe to the Americas.
The underlying science: Most of the DNA in our cells lies in the nucleus. But there are structures outside the nucleus, called the mitochondria. The mitochondria have several functions, the most obvious of which is that they are responsible for converting food into energy within the cell. The mitochondria also have their own DNA.
The DNA material in the nucleus, in the 46 chromosomes in humans for example, comes almost equally from the father and mother — 23 chromosomes from each. But the mitochondrial DNA comes only from the mother. This means that the mitochondrial DNA follows the female line exclusively. If a woman has no daughters, her mitochondrial DNA (mtDNA) line dies out.
Nuclear DNA (the 23 pairs of chromosomes in the nucleus) goes through a process called recombination, whereby the chromosomes that are passed on to the offspring, say through the mother, are a mixture of the genes in the mother’s lineage. However, the mtDNA is not a mixture like this, but comes exclusively from the mother.
Mitochondria have double-stranded DNA which contain ~16,569 base pairs that code for ~37 proteins. DNA replication in the mitochondria is independent of DNA replication in the nucleus. Neither DNA repair nor recombination is involved in mitochondria DNA processes, which may explain why mitochondrial DNA has a 10 times higher mutation rate than nuclear DNA.The number of mitochondria varies between male and female gametes. Oocytes have 100,000 mitochondria and sperm have less than 100. Sperm mitochondria are destroyed shortly after fertilization.
It is thought that sperm mitochondria is tagged for destruction by the oocyte because it is seen as a foreign substance. This may explain why mitochondria is inherited only from the mother. This information initiated the use of mitochondrial DNA to reconstruct family trees and eventually led to the Mitochondrial Eve Theory.
The mitochondrial DNA was used to study lineages and to estimate dates of divergence among different groups. This is done through studying differences between the mtDNA sequences in different individuals.
The nature of the differences provides clues about the relationship between individuals, and the magnitude of the difference indicates how long ago the lineages of the two individuals in the maternal line diverged. There are complications in the process, but this is the basic principle.
Mitochondrial DNA from 147 people, drawn from five geographic populations, have been analysed by restriction mapping. All these mitochondrial DNA stem from one woman who is postulated to have lived about 200,000 years ago, probably in Africa. All the populations examined, except the African population, have multiple origins, implying that each area was colonized repeatedly.
First, mitochondrial DNA offer a magnified view of the diversity in the human gene pool. Mutations accumulate in this DNA several times faster than in regular DNA. Secondly, mitochondrial DNA is inherited maternally, thus, it is a useful tool for understanding the genetic relationship between racial groups. Thirdly, mitochondria within a typical human are usually identical to one another.
In a genetic study, mtDNA was highly purified from 145 placentas and two cell lines, HeLa and GM 3043, derived from a Black American and an aboriginal South African, respectively. The results aimed to show and understand how mitochondria can be used to show the inter-relationship within and between the five populations studied.
Geneticists harvested 98 placentas from various sources, including those in the US, Australia and New Guinea. They created a sample study to represent the five geographic regions:
— 20 Africans (representing the sub-Saharan region);
— 34 Asians (originating from China, Vietnam, Laos, the Philippines, Indonesia and Tonga);
— 46 Caucasians (originating from Europe, North Africa, and the Middle East);
— 21 aboriginal Australians, and;
— 26 aboriginal New Guineans.
From a tree of minimum length and the mapping, it was inferred that Africa was a likely source for the human mitochondrial gene pool, leading to African mtDNAs (types 37-41, 45, 46, 70, 72, 81, 82, 111 and 113).
On the basis of people with the greatest differences in their mitochondrial DNA, it was concluded that “the age of the most recent common ancestor (MRCA) for mtDNA, on the basis of the maximum distance between two humans (5.82 x 10^3 substitutions per site between the Africans Mkamba and San), is 171,500 ± 50,000 yr BP”.
Conclusion
The theory of Mitochondrial Eve is supported by numerous anthropological findings. The partial remains of a 1.75 million-year-old fossil were found. The oldest modern human remains were first found in Africa, while younger remains were found in the Middle East, Europe and Asia. This supports an African origin for modern humans.
The writer works as an associate professor of biochemistry for the Ziauddin Medical University, Karachi
|
|
|
|
