Gene Swapping Variety is indeed the spice of life. That is the message of THE MATING GAME, Part 2 of NATURE’s six-part TRIUMPH OF LIFE series. It takes a passionate look at the evolution of sex, which allows a species to pass its genes along from generation to generation.

Sex is everywhere. Bees do it and birds do it — and so do lizards and bacteria. In its simplest form, sex is the process of mixing genes from two parents into a new offspring. This gene swapping ensures that each generation is just a bit different from the one that came before, and that each individual is a bit different from others.

This variation gives the species a better chance of surviving changing conditions. A few individuals, for instance, might be able to survive a deadly new virus and carry on the species, while the rest die. Eventually, the virus-resistant newcomers might even evolve into a new species.

Just because sex is everywhere, however, doesn’t mean that all organisms do it the same way. Evolution has produced virtually every conceivable combination of mating behaviors, as THE MATING GAME shows.

A male’s bird’s bright plumage is more than just eye-catching. Colors can also tell a potential mate about the man’s health a vigor.

In some species, for instance, the males compete with each other for the chance to mate with females. But in others, it is the females who vie to be the more attractive mate. Sometimes, the female is bigger, in order to hold more eggs. But in others, such as humans, the male is typically a bit larger. In some species, the females do most of the hard labor of child rearing; in others, it is the male that does all the work. And in some species, such as many marine fish, the kids are left to fend for themselves.

Other animals have evolved especially creative approaches to sex. Some female lizards, for instance, don’t need males to reproduce. Each female can lay eggs that produce “clones,” or genetically identical baby lizards. While cloning allows the species to reproduce under very harsh environmental conditions, it also leaves the identical offspring much more vulnerable to disease or environmental changes.

Some marine worms have taken another approach — each individual is both male and female. These “hermaphrodites” have the option of being mother or father. And a few fish take the idea in another direction. They can change sexes depending on circumstances, spending part of their lives as males and part as females.

It all goes to show that sex is never simple. But it has proven an essential engine for the evolution of life on Earth.

Choreographed Cooperation Life may be a contest in which only the fittest individuals survive, but cooperation has also played a key role in evolution. WINNING TEAMS takes a close look at the alliances that animals have forged — with others of their own kind and very different organisms — in a bid to stay alive. In fact, teamwork occurs everywhere, from flocks of birds and herds of wildebeest to colonies of ants and termites.

For some animals, the motivation for joining together is defense. A flapping, pirouetting flock of birds, for instance, can make it harder for a hungry falcon to home in on a single victim. Similarly, a thundering, shifting herd of wildebeest can be an intimidating — and confusing — sight to a hungry lion. And in both cases, there are more eyes to keep on the lookout for attackers. There is, indeed, safety in numbers.

Not surprisingly, some predators have responded to herding defenses with teamwork of their own. Feeding dolphins, for instance, have been known to work together to herd schools of fish toward the surface, where the seafood meal finds it harder to hide. Lions also team up to spring the trap on wildebeest, with several lionesses needed to topple one of the big beasts. And early human hunters, of course, learned to work together to hunt creatures, such as woolly mammoths, that were many times their size.

In many insect societies, every individual in a hive or colony can be the offspring of a single queen, making them all siblings that share genes.

Other times, however, the benefits of teamwork are less obvious. Animals that feed together, for instance, can spread out and cover more territory, making it more likely that one will hit a mother lode of food. The strange Damaraland mole rats featured on WINNING TEAMS, for example, drill through the soil as a team of up to 40 family members, looking for the roots and tubers that fill their empty stomachs. For years, researchers were unaware of this choreographed cooperation, since the underground-living rats are quite secretive.

Similarly, the link between some plants and the birds that eat their seeds took years for researchers to recognize. These plants, which include some wild rose bushes, produce tough berries that, if dropped on the ground, won’t sprout. But if the same seed is eaten by a bird, and is then etched and cleaned by the bird’s stomach acids and excreted onto the ground, it is ready to germinate. Similarly, some flowers can be pollinated only by a particular insect. The arrangements have led some scientists to ponder who is getting the better deal: Are the birds and insects slaves to the plant, or is it the other way around? The answer lies in their “symbiotic” relationship — meaning both organisms benefit mutually from the other.

Often overlooked is the important role that microscopic organisms play in the lives of many plants and animals. Some of these “symbiotic” bacteria live on the roots of plants, helping them draw nutrients from the soil. Others reside in the stomachs and intestines of everything from termites to humans, helping to digest food and remove toxins.

Without us, our stomach bacteria would die. But without the bacteria, we might fall prey to illness. It’s a classic case of the evolutionary ties that bind all life together in the drive to build highly competitive — and ultimately winning — teams.

Evolving For Advantage On some ancient battlefield, an early human soldier realized that a sharpened stick could become a deadly spear that would send the terrified enemy scrambling for safety. In response, the defeated soldiers came up with their own innovation: wooden shields that blunted the spears and suddenly turned the tables. It was then up to the attackers to devise another new weapon that could defeat the shields and restore their advantage. An arms race was born.

But it was far from the first. For billions of years, life on Earth has been engaged in its own ETERNAL ARMS RACE, the subject of Part 3 of NATURE’s TRIUMPH OF LIFE. As predators became better hunters, their prey also evolved better defenses.

The cheetah and its main prey, the Thompson’s gazelle, are the two speed champions of the Africa plains.

This drive to survive has produced remarkable hunting strategies, from frogs that are able to snare flying insects with long, elastic tongues, to cheetahs that work together to chase down fleet gazelles. But it has also shaped magnificent survival skills. Some moths, for instance, can sense a bat’s prey-seeking sonar pulses, and duck just in time to avoid the onrushing bat’s jaws.

Other animals have taken to deception, evolving colors and body shapes that provide perfect camouflage, making them invisible to predators. Some octopuses featured on THE ETERNAL ARMS RACE, for instance, can make themselves look just like poisonous sea snakes. Still other animals have taken the opposite tack, covering themselves in bright, outrageous colors that make it impossible for them to hide, but advertise the fact they can be distasteful or poisonous to eat. In the competition between hunter and hunted, no new tactic — from thicker armor or sharper teeth to better vision and hearing — is left untried. But only the successful traits — those that either let a predator catch more prey or allow the prey to survive attack — get passed along to the next generation. Meanwhile, the ultimately unsuccessful adaptations get left behind on evolution’s battlefield, victims of life’s eternal arms race.