Food: Bipedalism, Teeth, Brain

Why does the human body look the way it is? While I suppose it could have magically appeared in its present form ex nihilo, it is more likely to have evolved from existing structures to adapt to the surrounding environment. Why am I thinking about this? Because I’m reading the fascinating Story of the Human Body by Daniel Lieberman, a professor of human evolutionary biology. 

 

The forerunners of the Homo genus show up in the fossil record some 6-7 million years ago. Then between 2-4 million years ago we have a bunch of Austropithecus fossils, of which Lucy is the most famous. Then comes Homo habilis somewhere around the 2 million year-old mark followed by its cousins. The last of these, Homo sapiens, shows up 0.2 million years ago thereabouts. The boardgame Origins How We Became Human begins somewhere in this time-frame leading up to modern day technological and polluting humankind, and you one can spend many hours simulating all of this in a fun yet challenging game.

 

Homo shows up as an ice age is beginning. Food is getting sparse. The climate is getting colder. While our close cousins, the chimpanzees, are still well-adapted to life in the trees and eating fruit, even they have to chew on bark and other plants in lean times. Homo starts to find a different niche. We are one of the few animals that spend much of our waking hours in the upright position, on two legs. And before comfy sofas, we walked a lot more. The savannas and grasslands require more walking and less swinging through the trees. Freeing our hands allows us to create better tools, whether it be digging for tubers or getting energy-and-nutrient-rich meat. It’s all about food. Eat or die. And most animals spend most of their lives looking for food and eating it.

 

We’re not as fast or as fierce as lions. We don’t have the speed to bring down a running antelope and rip its flesh with powerful jaws and teeth. But a group of us can run down an antelope eventually. We are one of the best long-distance runners in the animal kingdom, with thin hairs and sweat glands that allow us to keep going without overheating. And we have our hands free while doing it. Lieberman covers the wide range of anatomical adaptations from head to toe that allows us to do this. From the way our head sits and bobs around on our neck to the arch in our foot and the size of our big toe, we are long-distance running machines.

 

I didn’t realize how much you can learn from fossil teeth. Lieberman goes through this in detail while keeping the reader engaged, which is no mean feat. And he does calorie counts to estimate how much our forebears might have to forage or hunt to stay alive. Processing our food to make it more efficiently digestible – by pounding, chopping, cooking – also led to adaptations in why our jaws and teeth are different from our chimp relatives. You can see the process of change through the fossil record from the various Austropithecus through the Homo hominids. And to have efficient energy stores, we need fat. We are fatter than most, even in the distant past, not to mention today – where our bodies still crave the fat and we get so much less exercise driving our cars to the supermarket and foraging in the aisles of abundance.

 

To get the meat, it is more efficient to hunt in groups. And men do this best since they don’t have to physically nurse children. But to communicate and coordinate and thrive as a social community, we need to expand our skill set beyond our dexterous hands. That requires growing our brain – an efficient prediction machine that helps us size up our immediate situation and act accordingly. I learned that our guts are about equal in relative weight to our brain, unlike our chimp relatives with much smaller relative brains. Our brain is energy-hungry and we have to keep it well fed. To do so, we store fat that we metabolize into glucose to keep the energy supply constant and reliable.

 

All this makes me think about my origin-of-life research and protometabolic systems. What do living systems need? Food to stay alive. And with a little more excess, organisms can grow and reproduce. Humans are particularly adept at accumulating more energy than we need for our daily sustenance, especially once better tools and hunting weapons, not to mention cooking, became part of our daily routine. Better to save up for those cold, icy days. Except for photosynthetic organisms that can transform carbon dioxide from the atmosphere, the rest of us have to get our carbon building blocks from other sources: plants, animals, fungi, and other organisms dead or alive. To survive and thrive, a metabolism needs to be efficient and the food gathering needs to improve. I need to think about this at a chemical level. It’s hard for me to imagine, but I can make analogies to what larger organisms do in their quest for food and nutrition. Ultimately it all comes down to grabbing energy to stay alive.

 

P.S. I also did not appreciate how good humans are at throwing objects with precision. Our arms, shoulders, hand-eye coordination, all kept in balance, are amazing!

Stoichiometry Blues

I don’t know why my G-Chem 1 students, on average, did much more poorly than expected on the most recent midterm that covered stoichiometry. While the midterm exam average for stoichiometry is typically lower than the other midterms, this year it was substantially lower, far outside the norm.

 

Last year, my G-Chem 1 exam averages were similar in the first three midterms, so I think the range of academic ability in chemistry is similar between the two classes. I also have all four midterms at the same point during the semester (although there was minor moving around of topics). So, it shouldn’t have been Thanksgiving break that caused students to forget everything they learned. And some students still aced the exam. I even made sure to cover the last bit of stoichiometry the Friday before Thanksgiving break so that the many students who chose to miss Monday’s class wouldn’t miss the last section on redox reactions.

 

What’s different? The main change I made in my G-Chem class was to ditch the online homework system and its accompanying textbook. Instead, I assign some homework and “collect” a subset of it to grade. What I collect is clearly less than what I had previously assigned in an auto-graded online homework system. It’s possible that students are not doing the other suggested problems that I don’t collect. (Some certainly do, when they come in with office hour questions or turn some of it in even if I didn’t assign those as part of what I collected. But others might not.) But the questions I do assign are written the way I would write an exam question, so I felt that was helpful to students. This is unlike the auto-graded online homework system that often phrases questions differently.

 

None of this seemed to be a problem through the first three midterms. Students were doing similarly as they did in the past. I even asked for feedback from the students about how they felt about the changes I made and the majority seemed to like them and thought my study guides were helpful to learning the material. My current hypothesis for the difference is that when it comes to stoichiometry, the students need much more practice problem solving, and the changes I introduced caused at least half (or more) of the class to practice less compared to previous cohorts. This wasn’t as big a deal in earlier topics. Even though there were calculation type questions earlier in the semester, they weren’t as concentrated as when we covered stoichiometry.

 

I think I need to assign more problems or provide more time in class to work through them if I don’t want to be doing more grading. And given that I’ve jettisoned the textbook, I should move stoichiometry earlier. (We’ve been using “atoms-first” textbooks for many years that shift stoichiometry to the last third of the semester. I didn’t want to make too many major changes compared to what I did last year.) I also think the Thanksgiving break causes students to forget what they learned, but I suspect this wreaks more havoc for stoichiometry than other topics, and this year there was a double whammy when the students didn’t practice enough.

 

Thankfully for the students, I drop the lowest of the four midterm scores, and that will be the case for the majority of students in my G-Chem class this semester. That was also true last year (stoichiometry always has the lowest average), but the average scores were nowhere as low as this year. So the overall student grade hasn’t been impacted yet, but it may mean that many students need to beef up their stoichiometry problem-solving skills before the final exam. While the final exam is cumulative, so stoichiometry might be 20-25%, that’s still a substantial portion. Some students have come by to talk, now that they realize what they missed so that’s a good sign. Hopefully more do so.

 

There are two other possibilities for the lower-than-expected exam scores. It’s possible the exam was harder this year. I don’t actually think so, but since instructors are inflicted with the curse of knowledge, I can’t say for sure. I’ve been writing exams for many years and I’m confident that the exam I wrote was about right, but it could have been a tad harder – certainly not so much more difficult to cause the substantial drop in scores. It’s possible I have an academically weaker class this year when it comes to stoichiometry and math-related chemistry problems. My G-Chem classes are small, often less than 30 students (although it can be as high as 40) so there can be substantial differences from one group of students to another.

 

In any case, I need to think about some changes I’d like to make to my G-Chem 2 class next semester that is certainly more math-heavy. I am teaching the Honors section and the students who register for that class are self-selecting so I might not run into the same issue. Certainly I need to make changes to my G-Chem 1 class next year if I continue not to use an online homework system and textbook.