When Prometheus came out in the summer of 2012, it wasn’t just the die-hard Alien fans that took issue with it. People with an interest in real science also had some problems with the film. Granted, there were plenty of silly actions in the movie by brilliant so-called scientists, like taking off their helmets on potentially hostile alien worlds, trying to make friends with an evil cobra-headed acid worm, and being unable to run in any direction but a straight line.
However, the question of a DNA match between humans and Engineers is maybe the most interesting element.
For a film that should have been grounded at least partially in hard science, there seemed to be some problems with its basic presentation of high school genetics. After Dr. Shaw (Noomi Rapace) brings the head of an Engineer back to her lab, only to have it spontaneous wake up and explode, she runs a DNA test on the head’s genetic material. A few seconds later, the computer screen comes alive with a graphic comparison, declaring a “DNA Match” to human beings.
So that got us thinking. If we ever find ourselves with an exploded kind-of-human head in our lab, what are the chances it will be a genetic match to our own DNA?
The Answer: About 99%
The closest living species to humans, genetically speaking, is the chimpanzee (and its close cousin, the famously sexual bonobo). Humans share 96% of our DNA with these great apes. However, if you eliminate DNA that is duplicated throughout these species’ genomes, humans and chimpanzees share close to 99% of unique DNA sequences.
Of course, when you’re talking about the 3 billion nucleotides, that’s still 40 million or so differences in the DNA between species. Still, that results in an uncannily similar genome from human to chimpanzee, which can be visualized and compared to other species.
So, if chimpanzees are that close to humans from a genetic perspective, it’s entirely possible for a species like the Engineers (which we supposedly descended from) to be even closer. After all, they certainly looked more human, aside from their rippling muscles, huge black eyes, and towering eight-foot frame.
But the Engineer DNA wasn’t really an exact match, was it?
Well, no. But then again, nobody’s DNA is an exact match to anyone else’s. Even identical twins, which start out with the same DNA during fetal development, have very tiny differences, which arise from minor changes during DNA replication.
The DNA similarity between two unrelated humans is approximately 99.9%. In essence, this means that only one in every 1200 to 1500 nucleotides are different in any two people. Still, that means there are millions of differences between people on the genetic level, which results in the great diversity of our species.
Aside from the picture of what appears to be a representation of specific DNA markers (which is scientific argle bargle considering this is used for specific markers used in DNA profiling to compare the 0.1% difference in two humans), the possibility of finding this “DNA Match” between humans and Engineers is actually scientifically sound. If Dr. Shaw’s DNA sequencing computer assumes a 0.1% margin of error for two subjects to be a species match, the Engineers could be essentially human with only that tiny sliver of a difference.
But what about their awesome pecs?
When it comes to the appearance of a species, it’s not the proportion of unique DNA that makes the difference. Instead, it’s how the genes present themselves. Many of the differences we see between species of such similar genetic history result from genetic regulatory mechanisms. Basically, these mechanism are responsible for actually using the DNA in a gene to manufacture the proteins necessary for a specific trait. In other words, were you to turn on some of a person’s dormant DNA, they might end up looking more like a chimpanzee than a human being.
Visit the state fair, and you might wonder if someone hasn’t already tried this.
Getting back to the Engineers, it’s possible that their very obvious differences (including their size, musculature, pigmentation, and even potentially their intelligence) theoretically could be a result of our own genes that haven’t been turned on.
So, while Prometheus is loaded with scientific inaccuracies and logic problems (though I still quite enjoyed the movie, myself), it’s not entirely off-base on its presentation of Engineer genetics.
Now, if we could just explain what the hell was happening with the oily goo evolution into an almost-xenomorph. That’s a much tougher mystery.