Episodes 6 of Cosmos, Travellers' Tales, doesn't try to answer this question. It chooses to celebrate the that the "the passion to explore is at the heart of being human." We all need reminders of this sometimes, especially these days, when our newfound security, wealth, and comfort work to dissuade us from the expense and risk of exploration - slowly seducing us to the same fate as poor homo neanderthalensis.

Travellers' Tales is a thematic sequel to episode 5's Blues for a Red Planet, though I think it works better as an hour-long piece of entertainment. Both Voyager and Viking could trace deep roots in our culture and common history. Both exemplified the best of us, representing a purity of vision. Unlike historical sailing missions of exploration, both Viking and Voyager were untainted by greed, war, disease, and conquest. Their missions were peaceful, their goals scientific. Voyager ultimately became the more famous of the two, I would argue. It revealed far more new, tantalizing worlds, stranger vistas, and continues to operate to this day. It also traces a greater lineage than Viking, which makes for a more profound story.

The show begins with a callback to our very first episode. We start outside and look in, traveling from the outer solar system towards the Sun, finding Earth (and ourselves) at the very end of the journey. But instead of jumping into history, Sagan takes us to the present (as it was in 1979, that is) with a look inside NASA's Jet Propulsion Laboratory, cigarette smoke and all, when scientists were receiving data as Voyager 2 flew by Jupiter in 1979.

The parallels are drawn heavy between the Voyagers and the sailing vessels of second great age of exploration, when Europe came to dominate much of the world. Both types of ships travelled great distances over many years, both explored new lands, and both returned tales of adventure and discovery. Unlike the sailors, though, the travellers' tales returned by Voyager are always true. There are no fanciful, mis-remembered mountains lurking in the haze of Titan or shimmering creatures seen after a rum-drenched night of staring into the clouds of Jupiter. Voyager only relayed the data with a cold sobriety, leaving us to our to our wits to spin the fanciful interpretations of worlds of ice and fire and shattered crust.

After a highlighting the Dutch enlightenment and their remarkably open, adventurous society, we get a brief glimpse at the great scientist Christiaan Huygens, who discovered Saturn's rings. We see his focused efforts to peer through the newly developed telescopes of the time, struggling to understand the new worlds he saw. We are then brought back to JPL, where we see another group of scientists struggling to understand the new worlds they saw, this time through Voyager's eyes. Our tools may have improved, but our desires to understand are the same.

These two spacecraft would continue to function far beyond when Sagan (or anyone) would have predicted. Just last year, I was part of The Planetary Society's 35th anniversary event celebrating the Voyager mission with its lead scientist, Ed Stone. Not only did Voyager 2 continue on towards Uranus and Neptune, but they both have continued on towards interstellar space. Both are still radioing back information, and Voyager 1 has now passed into interstellar space. While only a few instruments still function, they still carry with them the golden record, their welcome message, our species' way of saying, "we were here."

Svante Pääbo is the Director of the Max Planck Institute for Evolutionary Anthropology in Germany, where he specializes in sequencing the DNA of ancient creatures. He often asks himself the question of why humans were driven to explore and neanderthals were not.

There is a compelling argument that our drive to explore - Pääbo calls it our "madness" - is related a series of genetic mutations that are unique to humans. Variants of the gene DRD4, for example, have been linked to restlessness and risk taking, and Pääbo believes it represents the mutations that made us the type of species that looks across an endless ocean and thinks "let's see what's out there."

I don't think anyone seriously believes that our drive to explore is a work of a single gene, but I do see how a set of mutations of various genes could increase this tendency and thereby increase their likelihood for reproduction. By reaching out into new places, we exploit untapped biological niches for ourselves. We face animals that aren't evolved to hunt us. The flexible software of our brains could more quickly adapt to new surroundings, and in doing so the new surroundings would themselves select for our own adaptations that make us flexible. The drive for exploration and expansion in this sense can be considered a phenotype - the physical expression of a gene or set of genes in an organism.

But phenotypes don't just represent physical characteristics. Richard Dawkins expanded on the concept with his theory of the extended phenotype, which is any characteristic or expression in the world that helps in the survival of those genes, regardless of whether they are in the same body of the genes themselves.