Identical twins have always fascinated us - the idea of two people looking exactly the same questions our sense of individuality.
Last year, science finally proved that we're able to create identical copies of one another - clones.
And that has made us question exactly how unique the human race will be in the future. Will humanity eventually become the object of its own technology?
In the film 'Alien Resurrection', the star, played by Sigourney Weaver, is resurrected from the dead by cloning her DNA, and made into a lethal fighting machine by engineering her genes to include some of the DNA from the Alien.
Another movie coming soon is 'Gattaca' genetic engineering of humans in the future. But science fiction is, in this case, firmly grounded in science fact!
Dolly the sheep became the first mammal to be created by cloning. Dolly is the first animal to be created from a non-reproductive process with only one biological parent - the first true clone in history.
Professor Michele Ramsey of SAIMA at the University of the Witwatersrand explains the two different interpretations of cloning:
"You can take a cell and split it to produce identical copies. Another way seen by molecular biologists is cloning of individual genes, and that is removing a gene from its present context and putting into a different organism and making many many copies"
Until recently, cloning had been considered impossible. It had always been thought that as we (or any other animal) grow, and our cells become specialised - these cells cannot be made to revert to an embryonic phase of growth.
In other words, although a single human hair cell contains a complete genetic code - it can't be made to grow into another complete human - it's now a specialised hair cell and can only grow... more hair.
Or can it?
At the Roslin Institute in Scotland, scientists earlier this year turned nature on its head. By "starving" a mammary cell from a sheep, scientists, led by Dr Ian Wilmot, "convinced" the cell to regress to its embryo phase.
It was then fused with an unfertilised egg and implanted in a female sheep which then carried and delivered the lamb as normal.
The lamb will grow up to look exactly like its parent. Unlike most of us that share genetic material from both our parents, Dolly has almost the exact same genetic code as her single "mother".
The implications are enormous and to some... very frightening.
At its most benign, cloning may be very useful in animal breeding and agriculture - like Gene the calf, the second mammal to be created by cloning, at ABS Global Inc, in Wisconsin, USA.
Beef producers will benefit enormously. They can clone a superior bull and then use multiple bull clones to produce semen with a similar genetic makeup. The possibility of cloning extinct species has also been bandied about by the media, but how realistic is this Jurassic Park scenario?
Professor Ramsay believes that it is unlikely that cloning of extinct animals will happen, as one requires an intact DNA sequence, impossible to acquire from extinct species.
However, the most pressing question is whether the next step is the cloning of human beings.
Already the cloning of embryos could be used to increase chances of success for infertile couples undergoing in vitro fertilisation. Dr Simon Fisher, from the Centre for Assisted Reproduction, in the UK, comments:
"In theory, yes we can clone human beings, but would we want to?"
He feels not, unless there was a way to ensure healthy life to a sick individual:
" ...you take the cells which have gone sick in the child, which are now healthy from the cloned embryo, and you inject them into that child. You have cloned the child's cells, to produce healthy cells, which gives the child life."
Human cloning may also allow us to finally answer the age old question that has divided all of the human sciences: what makes us what we are - our biology and our cells - or our environment and upbringing?
We must question what makes us human - is it our bodies, or the minds within - and can the two be separated? What comprises the human soul?
Dr Fisher continues:
"We are more than the sum product of our genes. We are also the product of our experience. I would have to be brought up with exactly the same parents, under identical circumstance to become me -the me beyond what you are looking at: the me that is inside of me. And even then, I probably would be subtly different to what I am."
The future always brings with it new ethical questions. How far can we interfere with nature, and what exactly does it mean to be human? We may not like the answers - but the cloned cat is now out the bag and there's no simple way to put it back in.
Dr Simon FisherCentre for Assisted Reproduction
Tel:(SA office - Sue Ivins:) +27 16 66 1320
Dr Michele Ramsey
Roslin Institute, Scotland, UK:
SAIMA, University of the Witwatersrand
Tel: +27 11 4899214
Tel:+44 (0)131 527 4200
Fax: +44 (0)131 440 0434
ABS Global Inc, Wisconsin, USA:
Tel: +91 608 846 3721
Fax: +91 608 846 6446