Are our fates determined by the stars or by our actions? An age-old debate made no less contentious by reducing the loci of those forces to our genes or our behavior — a new study in Cell Reports chips aware at the free will side of the argument. The question asked, can complex behavior be explained by genetics; the participants, our friends the mice; looking for food; the methodology, a bit of observation, a dash of machine learning, and a full cup of statistical analysis.
The researchers began by presenting the mice with a simple landscape of sand, with several “wells,” one of which contained seed to eat. Spend a day or two to get familiar with the layout, fast on day three to get a little hungry, and on day four search for the seeds, now buried in a different well. The last day included a bit of exploration, and a bit of foraging and all the moves, positions, and velocities were recorded. Question 1, could these complex actions, in the service of getting food be reduced to several “modules?” Module, at least to me, suggests a turn left, walk 20 feet, type of instruction; but put that idea aside and think of these modules as more like a series of irreducible patterns.
Using all that data and a bit of algorithmic magic the complexity of foraging was reduced to about 13 “behavioral measures” which in turn describe 71 modules – not clearly understood by us analog types, but reproducible across the range of experiments with the mice. 55% of mouse behavior could be explained by those modules, the remaining 45% by action that could not be categorized or classified. Now here is where the rubber hits the road and the experiments get interesting, through the help of statistical analysis.
These 71 building blocks were not applied randomly, “one type significantly influences the nature of the next…” – they were chained to one another in a pattern to form a larger pattern. Next, they found those building block patterns could be assigned to more granular behavior, how much was eaten, how closely the mice hugged the maze walls, presumably fearful of predators, versus wandering in the middle, and how often one kept at one activity over another (perseverance).
Independent foraging is a mouse milestone, for humans, I suppose it must be somewhere between sixteen and twenty-two, except in those cases where there is “failure to launch.” Younger mice expressed more modular excursions, but as they grew older and became adults, non-modular behavior became more frequent. Moreover, some modules were only expressed by the young, others only by adults – modules were expressed over a timeline of maturity. It was as if, the young ones learned the basics and then as they got older improvised – as we might see in any skill or craft.
In the final consideration, they looked at two different genetic strains of mice and their interbred offspring. They showed a significant statistical correlation between modules and an individual’s genotype; suggesting that modules are expressions of genotype. In an intriguing finding, although one familiar to any parent of teenagers, the researchers found that parental genes greatly influenced their children when they became adults, but showed little correlation when the offspring were juveniles. They also demonstrated by at least in the case of gene, Magel2 for those who absolutely have to know, the presence of one, two or no copies altered the expression of a distinct set of behaviors.
The researchers have demonstrated, primarily in a statistical way, that genetic expression influences behavior, not merely appearance. As those expressions are turned on and off, our behavior alters. So, you have to give the determinism crowd a few points. But for those of you still rooting for free-will, there remain two sticking points. First, as the mouse got older, non-modular behavior, the improvisational riffs, increased; second, there is a growing body of literature that shows our actions, like diet and exercise, can moderate gene expression. So free-will remains clearly in the running.
Source: Complex Economic Behavior Patterns Are Constructed from Finite, Genetically Controlled Modules of Behavior. Cell Reports. DOI: 10.1016/celrep.2019.07.038