DNA, Deoxyribonucleic Acid, an acronym that straightaway reminds everyone of the biology classes back at school…!!.. A molecule consisting of genetic instructions of living beings forms the basis of Genetics.
I know these details of biology might be supernumerary but our greed for unique snapshots of ancient times makes them obligatory. To get a detailed insight into the evolution of population and species, Ancient DNA was introduced in the 1980s.
Human curiosity forced geneticists and archaeologists to work together. The unresolved queries about past homo sapiens brought an altogether new technique.
Come let us dig some more to have an overview of this enigmatic technology.
What is DNA?
DNA stands for Deoxyribonucleic Acid is a molecule composed of two polynucleotide chains that coil around each other to form a double helix carrying genetic instructions for the development, functioning, growth and reproduction of all known organisms.
DNA consists of two strands known as polynucleotides. Each nucleotide is composed of one of four nitrogen-containing nucleobases Cytosine [C], guanine [G], adenine [A] or thymine [T], a sugar called deoxyribose, and a phosphate group.
What is Ancient DNA?
Ancient DNA or aDNA refers to the DNA extracted from specimens that are dead for decades, hundreds or sometimes thousands of years. It is a technology to first, recover intact DNA, and then sequence the DNA.
Genetic material has been recovered from paleo/archaeological and historical skeletal material, mummified tissues, archival collections of non-frozen medical specimens, preserved plant remains, ice and from permafrost cores, marine and lake sediments and excavation dirt.
The first study of aDNA was administered in 1984, at the University of California, Berkeley by Russ Higuchi and colleagues. The study reported that traces of DNA from a museum specimen of the Quagga have remained in the specimen over 150 years after the death of the individual, but could be extracted and sequenced.
This revelation led to a series of developments in aDNA, listed out below:
In the next two years, Svante Paabo, a Swedish geneticist confirmed that aDNA could successfully investigate mummified specimens too, which dated back as far as thousands of years.
Post PCR development era in the 1990s ushered in successful findings from millions of years old specimens.
Sequences of insects such as stingless bees, termites, wood-gnats and plants from the Dominican era dating to the Oligocene epoch were established.
The revolutionary success was accomplished when studies reported Dinosaur DNA sequences to have been extracted from a Cretaceous egg.
The 2000s brought in cheaper research techniques to the field of aDNA. Single-stranded DNA has sparked a new frenzy in aDNA researchers.
In this way, we can see that Ancient DNA has brought us nearer to our extinct companions who once tread the Earth.
The oldest DNA was reported in 2021, in the teeth of mammoths that lived in northeastern Siberia up to 1.2 million years ago. A mammoth was a kind of early elephant that lived during the Ice Age.
According to researchers, DNA specimens from the remains of three mammoths were recovered and sequenced. Though they were discovered back in the 1970s only but lack proper technology to find and remove the DNA.
The oldest of the three mammoths was discovered near the Krestovka River in Siberia and lived about 1.2 million years ago.
Another was found near the Adycha River and was between 1 to 1.2 million years old.
The third, near the Chukochya River, was around 700,000 years old.
The mammoth DNA was extremely degraded into very small pieces and scientists had to assemble billions of DNA pieces to get the sequence.
Humans were always too inquisitive about gathering knowledge about themselves, their origin and the evolution of the population. Mummified tissues of ancient humans are used as a source of ancient DNA.
The specimens of human DNA are both naturally preserved as well as artificially preserved tissues. Examples of natural specimens are –
Otzi, the Iceman was preserved in the ice
High altitude mummies from the Andes mountains, preserved due to desiccation
An example of artificially preserved specimens is the chemically treated mummies found in Egypt. But they are a limited resource.
The most useful to extract DNA are the archaeological record – Bone and Teeth.
As of 2021, the oldest completely reconstructed human genomes are ~45 000 years old. Such genetic data provides insights into the migration and genetic history – e.g. of Europe.
Complications and Obstacles
Our capable scientists face countless hardships to gather accurate DNA sequences. Some of the notable adversities confronted by them are as follows:-
The most commonly faced problem is the contamination of modern human DNA by microbial DNA.
A DNA may contain a large number of postmortem mutations, increasing with time.
The studies on the chemical stability of DNA have resulted in concerns being raised over previous results.
Degradation of specimens
Due to degradation processes (including cross-linking, deamination and fragmentation) ancient DNA is of lower quality in comparison with modern genetic material.
Even under the best preservation conditions, there is an upper boundary of 0.4–1.5 million years for a sample to contain sufficient DNA for contemporary sequencing technologies.
What questions will Ancient DNA answer?
The answer to certain questions can be given by DNA Sequencing. Many of the conclusions drawn from Ancient DNA are as follows:
To gather information about the ancient lives
Evolution of the Neanderthals and Denisovans
Extinction of Mammoths
Some revelations about living beings’ such as changes in the structure of the voice box in modern humans.
Crops which were grown by neanderthals
Mammals from the ice age
Recent extinction of animals like the dodos in New Zealand, the Tasmanian wolf in Australia and the passenger pigeon in North America.
Something will always be left…
I know this was just a sneak peek into the method of traversing the path towards finding our origin. But the fact is undeniable that the expedition is quite arduous and unusual. Not a bit conventional…..
We, humans, have always been enterprising and hoping to unravel the puzzle of human life. A perpetual search might alleviate our uninterrupted questions which are WHY, WHEN and HOW?
It’s intriguing to find that we have come a long way leaving many mysteries unsolved, which happen to be about us only. No worries now we can study new details on lost chapters in the history of the human race and understand how we became who we are today……
-by Sambhavi Yadav