"The similarities to humans are apparent," Michaelson said. "[The theory] could explain a lot of other things in development."

Scientists Skeptical

While reluctant to comment on a yet unpublished paper, other scientists interviewed said they are skeptical of the new theory.

"Cell death during development of the embryo is a well established phenomenon," said Bjorn R. Olsen, Hersey professor of anatomy. "It would be a radical idea--a catchy phrase, perhaps," he said of Michaelson's theory.

Olsen admitted that competition did exist locally between cells. Cells compete for growth factors, and those who have more receptors for the factors survive, he said.

But Olsen said, the term "battle for survival" is a bit drastic.

Similarity to Nervous System

Gregor Eichele, a researcher at Baylor Medical School in Houston, Tx., said that the theory reminds him of cell death in the central nervous system, which has been known of since the 1930s, he said.

But Eichele added, "I also feel that selection is not really random. Very specific regions undergo cell death, and they are always the same," he said.