Scientists say humans have genes that direct the body to grow new arms and legs after an injury but the genes lie dormant, a report in the Chicago Tribune said.

Hans-Georg Simon, a Northwestern University developmental biologist who discovered the genetic switch, and other researchers told the newspaper they think they can find a way to turn the genes on.

The project is financed primarily by the U.S. military, looking for better therapy for injured war-time personnel, the Chicago Tribune said.

Paralysed mice have been made to walk again by being injected with embryonic stem cells, a Californian company, Geron, claimed recently.

Geron’s announcement is just one of many that suggests humankind is on the verge of a scientific breakthrough that could change the treatment of disease and injury forever.

"Stem cell therapeutics are no longer relegated to the realm of theory," Randall Mills, CEO of Osiris Therapeutics, said. "They are coming and they will have a huge impact."

In scientific parlance, stem cells are "undifferentiated" cells that can divide and grow to replace dead or dying cells.

The goal of the research is a manipulable "master" cell on which human life is founded and from which cells, organs and tissues can be created.

It is just one of the exciting and controversial technologies on display at Insite, the science and technology exhibition to be held at the Sandton Convention Centre from September 24 to 27.

There is nothing new about using human stem cells in medicine. For years, bone marrow transplants and skin grafts have harvested the regenerative qualities of stem cells.

But stem cells taken from adults are inflexible. They are also rare and difficult to harvest. Those from a fertilised human egg, or embryo, though, have amazing potential. Catch one, give it the right bio-chemical spark and just about any cell, tissue or organ can be created which is identical to the original. The logical conclusion is that, eventually, we will be able to regrow lost limbs, replace damaged organs or substitute diseased tissues.

But underpinning the already tricky science are grave ethical dilemmas. The problem is that once embryonic stem cells (ESCs) have been harvested, the embryos themselves are destroyed. For many who see the intentional destruction of an embryo as murder, this is crossing a critical line.

But scientists announced a breakthrough at the end of last month, saying they needed only one cell from a three-day-old embryo to grow stem cells, allowing the embryo to live on.

Scientist Robert Lanza told the Daily Mail: "This will make it far more difficult to oppose this research." But the initial response suggested the ethical battle would go on.

In South Africa, fear of the dangers of cloning – which involves replacing the nucleus of an unfertilised human egg with the nucleus of an ordinary cell – is providing an obstacle to research on ESCs. When the first draft of the National Health Bill was published in 2002, local scientists were shocked. The Bill initially prohibited any form of stem cell research on the grounds that poor women were likely to be exploited.

Scientists such as Professor Udo Schuklenk, then at the University of the Witwatersrand, described the proposed ban as indefensible, saying the country "could benefit from a liberal stem cell research policy that attracts international scientists" and that clear guidelines could "ensure that risks of exploitation are minimised".

Since then, the parts of the National Health Act dealing with stem cell research have been rewritten and now represent, according to Schuklenk, "one of the most progressive legislations in the world".

The catch is that while the Act has been largely promulgated into law, the section dealing with ESS (Chapter Eight, section 56, which allows research to be conducted on embryos up to 14 days old) has not. This has resulted in a legal and scientific hiatus.

The section also stipulates that only research for therapeutic purposes will be allowed while "the manipulation of genetic material" or indeed any activity aimed at the "reproductive cloning of a human being" is prohibited.

According to Prof Ames Dhai, head of bio-ethics at Wits medical school, the uncertainties around ESC research and especially cloning continue to delay the commencement of these laws.