"Standard sexual reproduction among sexually reproducing species," Cainen said. "Some species need three or even four parents, but not many. It's too inefficient."

"No doubt," Sagan said. "Administrator, have you heard of Fronig's Syndrome?"

"It's a rare genetic disease among the Rraey," Cainen said. "Very rare."

"From what I understand of it, the disease is caused because of deficiencies in two unrelated gene sets," Sagan said. "One gene set regulates the development of nerve cells, and specifically of an electrically-insulating sheath around them. The second gene set regulates the organ that produces the Rraey analog for what humans call lymph. It does some of the same things, and does other things differently. In humans lymph is somewhat electrically conductive, but in the Rraey this liquid is electrically insulating. From what we know of Rraey physiology this electrically insulating quality of your lymph usually serves no particular benefit or detriment, just as the electrically conductive nature of human lymph is neither a plus or minus—it's just there."

"Yes," Cainen said.

"But for Rraey who are unlucky enough to have two broken nerve development genes, this electrical insulation is beneficial," Sagan said. "This fluid bathes the interstitial area surrounding Rraey cells, including nerve cells. This keeps the nerve's electrical signals from going astray. What's interesting about Rraey lymph is that its composition is controlled hormonally, and that a slight change in the hormonal signal will change it from electrically insulating to electrically conductive. Again, for most Rraey, this is neither here nor there. But for those who code for exposed nerve cells—"

"—it causes seizures and convulsions and then death as their nerve signals leak out into their bodies," Cainen said. "Its fatality is why it's so rare. Individuals who code for electrically-conductive lymph and exposed nerves die during gestation, usually after the cells first begin to differentiate and the syndrome manifests."