You can pick up any reasonably well written book and make a case for it being an exploration of what it means to be human, the state of humanity, or the universal truth of the human condition. Scalzi’s Old Man’s War series is very definitely asking what defines humanity.
In the universe of the Old Man’s War series, Scalzi pushes the envelope of humanity. Colonial Defense Force soldiers are created when
In The Last Colony, we return to the protagonist of Old Man’s War, John Perry. We rejoin Perry with his wife, Jane Sagan, a former special forces soldier created partially from Perry’s late wife’s DNA, and their adopted daughter, Zoe. Zoe is the daughter of the The Ghost Brigade’s antagonist, Charles Boutin. Perry, Sagan and Zoe have become settlers on the Colonial planet Huckleberry. Joining them in their life on Huckleberry are two Obin, alien creatures who worship Zoe (Read The Ghost Brigades). They are offered the opportunity to lead a new kind of human colony on a planet called Roanoke. Which really should have been a clue.
There are politics in the universe that I can’t go into without spoiling the previous books. One of the lynchpins of the series is where is the center of humanity? Is it Earth, the planet of origin kept separate from the universe? Or is it Phoenix, an older human colony which is the center of the Colonial Union?
In The Last Colony, the Colonial Union and a few other alien races have declined to join an alliance of races, The Conclave. The Conclave wants to end the cycle of war over colonies and slow the expansion of human colonies. The Colonial Union thinks it can continue to undermine the Conclave and colonize planets at will. The Colonial Union is a business, and colonies are how it grows. In it’s need to protect itself, the CU and the Colonial Defense Force (CDF) have stretched the definition of humanity. Elderly Earthers are transferred to genetically engineered bodies to become soldiers. Special Forces are created from a mishmash of human and non-human dna, born as fully formed adults. The consciousness of other humans are placed into bodies that can exist in the vacuum of space enabling them to act as stealth soldiers.
Off of Earth, the CU defines humanity, what it is and where it goes. The central conflict of The Last Colony is over whether or not they have that right. Though Scalzi’s plot is humans v other alien races out in the universe, it’s still a question of whether or not humans are capable of coexisting and collaborating with others for survival. The CU creates humans that are less and less recognizably human, but hangs onto humanity so tightly it may get humans eradicated from the universe.
In “Sagan’s Diary,” we hear Jane’s perspective on leaving the Special Forces and her relationship with John Perry. Special Forces soldiers are created as adults. They are analogous to Frankenstein’s monster, from the book, not the movies. “Real Born” humans may be uncomfortable with them, or even fear them. In her diary, Jane talks about very human emotions of fear, loss, loneliness, love and desire.
Again, Scalzi raises interesting ideas which he then skims. As I listened to The Ghost Brigades, The Last Colony, and Sagan’s Diary, I thought a lot about Carl Sagan’s “Pale Blue Dot” speech. Some day, we may live out in the stars. Whether we ever do or not, we need to deal with the health of this planet and the life on it. Otherwise, we just move our garbage offworld.