For the first time, scientists have made it possible for female mammals to reproduce without the help of males. Researchers say the technology is neither scientifically nor ethically acceptable for humans.

It only takes two female lizards to reproduce. But for reasons that are not entirely understood, humans and other mammals require male genes to procreate. Now, for the first fime, scientists have found a way to produce mice with two genetically-altered mothers, and no father.

In a landmark study, Japanese investigators accomplished the feat by rearranging the genetic material of two baby mice. They snipped the male DNA from the underdeveloped eggs of the newborn pups and inserted the remaining female DNA into the ovaries of two full grown, female mice. The inserted female DNA took on male characteristics and, after 457 tries, led to the pregnancy in two mature female rodents and the birth of two apparently healthy mouse pups. One of the babies, which scientists named Kaguya, matured and successfully gave birth to its own offspring.

Lead researcher Tomoshiro Kono of the Tokyo University of Agriculture in Japan says investigators wanted to see whether they could alter the roles of male and female genes. He says people shouldn't get too excited about the research.

"Before we discuss the ethical issue of this technology, it is totally impossible to apply this method to human beings,? Dr. Kono said. ?It is completely different from the case of cloning. It is totally impossible. This method requires a high level of genetic modification technology. We cannot apply this to human beings."

Besides, Dr. Kono says the technology would be extremely expensive.

Nevertheless, ethicist David Magnus of Stanford University in California calls the creation of a mouse pup from two females "a pretty big step," that might someday be within reach of humans.

?We can envision a future where it may be that lesbian couples may try and find ways of having offspring that are genetically related to both of them and not genetically related to any men who might be able to claim paternal rights,? Mr. Magnus said.

Some experts say the technology has implications for stem cell research that might cure diseases such as Parkinson's and diabetes. If healthy fertile mice can be produced using two female mice, they argue that perhaps stem cells can be grown by stimulating unfertilized human eggs.