Evolution (2001) Part II - "Selenium Could Be as Lethal to Them as Arsenic Is to Us"

Spoiler Level – Moderate-to-high

The Movie – Alien life arrives on Earth in a meteorite. As usual, the military is helpless. To save the day, a washed-up biology professor teams up with a geologist who would rather be coaching girls volleyball, a clumsy CDC researcher, a failed firefighter trainee, and two of the worst biology students to ever graduate high school. Pretty much a standard movie team.

It's really not a terrible movie aside from the bad science. The cast is strong, and while not all of the jokes hit, there are some good moments. It's hard for me to really dislike a movie where a biology professor from a community college gets to be the hero. Also, I think I tend to be more forgiving with comedies because absurd twists on reality are a big part of humor. Still, this movie might even beat out Mission to Mars for the highest density of bad science in a movie, and it must be addressed.

The Scene – The scientists are desperately trying to figure out how to stop the rapidly evolving aliens when David Duchovny's character has an epiphany. We're carbon-based, while aliens are nitrogen-based. If you move two spots down and one spot over from carbon on the periodic table, you reach arsenic, which is highly toxic to us. If you make the same move from nitrogen, you reach selenium, which they reason will be lethal to the aliens. The heroes realize they can find the selenium they need to kill the aliens in a popular brand of shampoo, and 16-year old me learns what product placement is.

Periodic table t-shirts are nice, but real scientists just go ahead and get it tattooed on their bodies. From Evolution.

The Science – Well, it would be fair to call us carbon-based life. And arsenic is certainly poisonous to us. However, those facts are not directly related. So there's no logical basis for suggesting that anything nitrogen-based would be poisoned by selenium. Let's look at the periodic table.

Elements on the periodic table do not actually attack each other like knights on a chessboard. Adapted from Wikimedia Commons.

The groups (columns), periods (rows), and blocks of the periodic table all represent important relationships between the elements. The most significant of these relationships is the groups. Elements in the same column behave similarly to each other; they share chemical properties that cause them to form similar compounds. The closer two elements are within the same column, the more similar they will be. Based on this, arsenic should be most like the elements phosphorus and antimony. What does that mean for us?

Well, there's a very important molecule called ATP, and the P here stands for phosphate, a chemical groups with a phosphorus atom at its core. ATP is a sort of molecular battery. During metabolism, when our bodies break down food for energy, that energy gets stored as ATP and used later when needed. Without it, we wouldn't have the energy to carry out the processes essential for life. And this isn't just true for people; ATP is used by every living thing we know of. Additionally, ATP is a building block for DNA, the genetic material of all known life.

So we have a phosphorus-based compound that's essential for life, and we have a toxic element just below phosphorus on the periodic table. You can probably guess where this is heading. Arsenic forms compounds that act similarly to phosphates, so our bodies accidentally use them when trying to make ATP. However, ATP isn't stable when it's made with arsenic. It breaks down before it can be used as an energy source or in DNA. When there's too much arsenic in our bodies, we can't harness energy properly or build or repair DNA, so we die. It all comes down to arsenic's similarity to phosphorus, not carbon.

Fixing the Scene – It's so easy to correct the bad science here while throwing in a real science fact at the same time. Just explain that arsenic is toxic to us because it mimics the phosphorus compounds our bodies use. Then assert that sulfur is important in the alien metabolism/genetic material and suggest that selenium will be toxic to them in a similar manner. It's no more complicated than the weird L-shaped rule they invented. It teaches an actual fact about science. And they can still sell shampoo. I'm actually kind of annoyed they didn't use this simple fix.

Next Time – There's so much more I can talk about with this movie, but I don't feel like dedicating the rest of the semester to it. So let's just have one more post of rapid fire complaints and call it a day.