Battlestar Galactica S4E21 (2009) -"Their DNA is Compatible with Ours"

Spoiler Level – Very high

The Show – Formerly a robotic slave race, the Cylons rebel against humanity by attacking the human home worlds with nuclear weapons and chasing the survivors through space. We're told the Cylons have some grand plan in mind (beyond genocide). We were lied to.

I enjoyed this show while it was on. It had some solid characters and dealt with some unique ethical questions. However, it definitely started to decrease in quality as time went on and the writers began to show they didn't really know where they were going with this. It's easy to find people complaining about how the show ended, but I think my complaints are a little different from the typical ones.

The science of the show is something of a mixed bag. There's no sound in space, which is a good sign someone cares about science. Faster-than-light technology is vague enough that you can pretend they're using something that theoretical physics suggests is possible. The biology is just vague to the point of being confusing. Cylons are robots, but some are similar enough to humans that it's impossible to tell the difference by any conventional method. The only way to tell is with a device that involves the core of a thermonuclear bomb. Cylons can't reproduce through normal sexual means, but humans and Cylons can if there's love involved. There's some strange theology at work here that's interfering with the biology.

The Scene – In the series finale, the remaining human and Cylon survivors are at peace and arrive at Earth 150,000 years ago. They find our ancestors and determine we're genetically compatible. The new arrivals decide to abandon all their technology and live with the early earth humans. The 38,000 survivors spread themselves throughout the planet, mate with the existing population, and thus become our ancestors as well. One important girl, the child of a human and a Cylon, is said to be Mitochondrial Eve, "the most recent common ancestor for all human beings now living on earth." Thematically, this is a cute way to demonstrate the enduring peace between humans and Cylons by saying that all people are the children of both races. Biologically, it's problematic. 

Star Trek's First Rule of Biology Research: When encountering an alien species, the first question that must be answered is "Can I make babies with them?" From Battlestar Galactica. 

The Science – Mostly I picked this episode because it references some really cool science that rarely comes up in pop culture. Mitochondrial Eve is a real concept. In all eukaryotic cells (animals, plants, fungi), there are tiny structures called mitochondria. Mitochondria used to be free-living bacteria, but one one of them was engulfed by a larger microorganism. And instead of being consumed, the two formed a symbiotic relationship. Mitochondria provide most of the energy for eukaryotic cells. Most of the mitochrondria's genes are with the rest of its host's genome, but some genes still reside in the mitochondria itself.

Mitochondrion diagram. It's not enough to have bacteria all around you and in your digestive track. You have ancient bacteria in your very cells, and you need them to survive. From Wikimedia Commons.

When an egg in fertilized, the sperm contributes the father's genomic DNA but does not transfer any mitochondria. Your mitochondrial DNA comes solely from your mother. Mitochondrial Eve is the most recent common ancestor of all human mitochondria, which makes her your matrilineal most recent common ancestor. In other words, if you went back in your family tree looking at your mother's mother's mother's etc and then looked at someone else's mother's mother's mother's etc, you would eventually reach a common ancestor. And Mitochondrial Eve is the most recent ancestor that can be described as the mother's mother's mother's etc of anyone on Earth.

This definition is a little different from how the term is described in Battlestar Galactica, but that's not what really bugs me. The idea of two independently evolved species being able to mate is ridiculous. The show even described the odds as "astronomical", but a better term might be "statistically impossibile." It could never happen. And it's not just that the Galactica humans and Cylons are compatible with Earth humans; they're genetically indistinguishable. Molecular biologists would be able to tell if there was a sudden influx of new genes 150,000 thousand years ago. The newcomers' DNA would even have to have all the same telltale signs that connect us to Earth apes.

There is no science to explain this, only "a divine hand at work" is suggested. And while I don't want to argue religion here, this bothers me. A deity that allows refugees to find a new population to mate with so the species can survive is one thing. A deity that manipulates our genetic code to hide such a major event in human evolution is something else entirely. When you have a god acting on that level, nothing in science can be trusted. Anything we think we know could just be the result of divine manipulation. In fact, that's the sort of deity Young Earth Creationists invoke to explain how the Earth can be less than 10,000 years old. "Sure, life looks like it's billions of years old, but that's just because God designed our DNA to make it appear that way when He created us in 4,000 BC." It's a terrible argument from them, and I don't appreciate it any more when it comes from one of my favorite science fiction shows.

Fixing the scene – This is more complicated than normal for me because biology and theology are heavily linked in this show. I sort of like the idea of humans and Cylons coming together to form the foundation for a new civilization. Just not our civilization. Let them form a new society that eventually develops to remind us of our own but is fully separate. I don't know if that really works with the show's theology, but I strongly believe in keeping science and theology separate. And that's the main lesson here. When science and religion are combined, one or both are going to suffer. That goes for fiction and reality.

Next Week – In honor of Fringe coming to an end last month (and the giant virus making a cameo in the finale just to spite me), I'm going to cover a season 2 episode on protein engineering.