Back in the early '70s, two science fiction writers -- trust-fund baby Larry Niven and ex-Trotskyite wingnut Jerry Pournelle -- got together to write a first contact novel which was published in 1974 under the name The Mote in God's Eye. The Mote of the title is a sun-like yellow star on the far side of the Coalsack Nebula. Orbiting this sun is a planet known as Mote Prime which is home to a race of aliens called Moties.
The single most important fact of the Moties' biology is that when a female Motie goes into estrus, she must become pregnant or she will die. Thus, Moties cannot practice birth control, and the race is locked into a permanent state of population explosion.
Of all the millions of animal species on Earth, there isn't a single one that replicates this feature of Motie biology. The reason is simple enough: an organism that dies when it fails to become pregnant is at a biological disadvantage to one that can live to become pregnant later on. During a famine, for instance, an organism suffering starvation (during which a preganancy would be fatal) will skip the estrous cycle, thus preserving its own existence. Any species that developed the Motie pregnancy-or-death trait would be at a competitive disadvantage and would eventually die out.
Biologically speaking, then, the Moties' pregnancy-or-death trait makes no sense. However, to two conservative writers like Niven and Pournelle, it makes perfect sense. Encouraging behavior by punishing an organism with death if it acts incorrectly is one of the defining characteristics of conservatism. Thus, it stands to reason that conservative writers would find a biological system based on punishment believable, and not wonder why there were no examples of it found in nature.
So it turns out that Stephen Colbert was right. Nature encourages reproduction using the liberal method of rewarding good behavior (by making sex pleasurable) rather than the conservative method of punishing bad behavior (by making abstinence fatal). Reality really does have a liberal bias.