Luke Skywalker’s Green Milk: “It’s Not a Breast. It’s an Udder.” And Other Science Facts You Didn’t Ask For
This past weekend, nerds worldwide set down their game controllers and curled up with their plush Chewbaccas to watch the DVD/digital release of the latest installment of everyone’s favorite space opera, Star Wars: The Last Jedi. Since the film was released in theaters, it has generated much discussion, from the multiple U-turns director Rian Johnson pulled with the storylines that the previous episode had set up, to whether Reylo is inevitable or a problematic perpetuation of the romanticization of male toxicity in film. These discussions left little room for the brief, dialogue-free scene in which Luke Skywalker is shown milking a giant semi-aquatic mammal then drinking straight from the tap.
Well, I am here to remedy that situation. And not unlike the scientists at the open-source science journal PLOS, who hilariously peer reviewed The Last Jedi, I’m doing it with SCIENCE.
The scene to which I refer involves Luke milking a creature who lives on the island and procuring a vividly green-colored milk that he messily drinks as Rey looks on.
Articles that have covered this scene have consistently called it “weird,” “gross,” and “bizarre,” nevermind the fact that 1.) We are a species that evolved to drink milk from a breast, and yet 2.) we think that is gross and, instead, choose to consume the milk of another species despite the fact that that it is nowhere near anything like our milk in composition, and 65% of us can’t even digest the stuff. But, I digress.
Today we’re gonna talk about straight-up nerd science. What I’m interested in, here, is not just the question of why the milk is green—We will get to that, but there is SO much more, here! In this brief, dialogue-free scene we are given several “clues” about this animal: various characteristics about its milk—not just the color, but also it’s viscosity, and opacity, and some very unique (and quite memorable) mammary anatomy. We also get some clues about it’s environment and behavior. But for the sake of brevity, I will be focusing mostly on the creature’s very memorable mammaries. If we take these clues and apply some of the known mechanisms (rules) of evolution from our own planet, we can make some guesses as to the evolution and social behavior of this creature. Let’s science the bantha fodder out of this!
The Last Jedi Visual Dictionary describes the Thala-siren as a “large, flippered marine mammal,” so we will presume that it is a mammal in that it 1. gives live birth, and 2. Produces milk for it’s young. (And also has hair and 3 middle-hear bones, technically.)
Mammalian milk is a living substance whose composition varies depending on the needs of the infants of a species—and even from hour to hour based on the needs of the infant, in response to either environmental stimuli or information communicated to the mother by the infant. For example, a mother may produce milk with a higher water content on a hot day, or produce antibodies to a specific pathogen within hours of coming into contact with it.
But one of the things that is most fascinating about milk is that its composition can–generally speaking—predict the caregiving behavior of that species (Tilden & Oftedal, 1997). The milk of a species like deer, for example, which may leave its fawn for up to 12 hours at a time to go forage, is high in protein and fat to provide sufficient energy to sustain the fawn through long periods without suckling. In total, the fawn may only eat 2 or 3 times a day. By contrast, primates (including us), have among the lowest protein and fat content and highest sugar content of the mammals. This is consistent with a species that carries its young everywhere, feeds with high frequency, and remains in constant contact with the infant 24-7. As parents and caregivers will note, human infants eat with pretty high frequency! Although, as primatologist Sarah Hrdy (Not a typo — pronounced “HER-dy n”) notes, relying on others for care or finding other ways to minimize the energy costs of caring for calorically expensive infants is not at all unusual from a cross-species or evolutionary perspective (Hrdy, 2009).
So with this information in mind, what can we deduce about the composition of the milk of the Thala-siren? And what might that tell us about its parenting behavior?