Week 8: Comparative Osteology

Physical anthropologists rely on osteology, or the scientific study of bones, to identify individual species, learn about the lives of an individual, or even to identify ancient illnesses (aka paleopathology). The skeletal features of bones reflect the life histories of individuals, and trained osteologists can use those features to identify the age, sex, diet, and, at times, even the cause of death of a particular specimen.

However, analyzing and comparing the bones from different species can also tell us about the evolutionary history of those species and the degree to which different species are related. For example, the overall form and organization of a dog’s skeletal features would be very similar to those of wolves, as those species are related. The same could be said for different species of fish, reptiles, turtles, etc.

In anthropology, osteologists often compare human skeletons with those of other primates so that we can learn about our ancient human past. In today’s activity, our TMSE students compared cranial features of human, chimpanzee, and coyote skulls, to learn about cranial capacity, dental formulas, diet, and the overall degree of similarity among species. For this activity, students were encouraged to think about the similarities and differences between each of the individual specimens. If they are similar, what makes them similar? If they are different, then how could we explain those differences in an evolutionary context?

To begin with, the students compared the skeletal characteristics of human, chimpanzee, and coyote skulls. Students were able to identify the human skull and distinguish it from the chimpanzee skull rather quickly, but additional analysis was needed to characterize precisely why the students thought they were so different.

skulls

The human chimpanzee skulls differed, for example, in the size of the teeth, the size of the cranium, and even the shape of the skull itself. Students also learned a new term, prognathism, to describe the degree to which the facial features extend out from the face. Chimpanzees are definitely more prognathic than humans, as are coyotes. However, the human and chimpanzee skulls were more similar to each other than they were to the coyote, which had a completely different structure.

 

In seeking a better way to describe the possible differences and similarities, we then analyzed two key features on each skull: teeth and cranial size.

To analyze the similarity in dentition, students were asked to come up with the dental formula for each specimen. A dental formula is essentially a count of the different types of teeth for a specimen, beginning with incisors (cutting teeth in the front of the mouth), canines (teeth for slashing), premolars (for stabilizing food and for grinding); and molars (grinders).

teeth

By counting the tooth types for the human, chimpanzee, and coyote skulls, our TMSE students figured out that humans and chimpanzees have the exact same dental formula! However, coyotes have a different formula.

Our students quickly ascertained that this similarity is likely due to the fact that humans and chimpanzees are related, both as primates and by our shared evolutionary past.

 

To continue to address some of these differences, we then compared the size of the cavity that houses the brain, also known as the cranial capacity.

cranial

By comparing across species, our students figured out that humans have the largest brain, followed by the chimpanzee, and then the coyote. After a lively discussion of the brain size of dolphins, humans, dinosaurs, and dogs, we reached the conclusion that our human brains are MASSIVE relative to our body size. Which, of course, means that we are intelligent creatures.

Our comparative analysis led us to hypothesize that the dental formula and cranial capacity may help determine whether a particular specimen is related to humans or not. To test out our theory, we then threw an unknown skull into the mix. After figuring out the dental formula, describing the tooth size, and looking at the cranial characteristics, our students concluded that the unknown skull was, in fact, related to humans because it shared a dental formula and had a cranial capacity that was in between that of the human and of the chimpanzees.

As it turns out, our students were absolutely correct! The unknown skull was Australopithecus afarensis, one of our evolutionary ancestors.

This activity ended up being a lot of fun, as everyone got a chance to handle castes of skulls and learn about how physical anthropologists may characterize skeletons. Moreover, by learning about basic skeletal features and interspecies variation, our students were able to conduct a comparative analysis of those features and to critically analyze the results based on that analysis.

All in all, a great day!

 

The lesson plan for this activity can be downloaded here.

Week 8 Skeletal Features

Week 6: Genetics

Hello all!
This week’s lesson tackled genetics. This lesson was the start as we enter the biological anthropology realm. Genetics is important to the field of anthropology for it allows us to shed light on the molecular similarities that all individuals share.
The students were taught the basics of DNA and how to differentiate between one’s genotype (genetic make up) and phenotype (outward, physical, expression of genes). The class activity that was done for the day examined various traits across students in the class. Using a list of traits (presence of a widow’ speak, hitchhiker’s thumb, attached earlobes, etc), the students were able to identify whether or not they had a trait and group with other classmates who shared that same trait.
The goal of this exercise was to exemplify the diversity that is accounted for by genetics. Each of the traits we looked at had the possibility of either being expressed as being dominant or recessive. The students were not told prior to the exercise what exactly it meant to be “dominant” or “recessive” but quickly picked up on the fact that those terms have nothing to do with the frequency that which they occur–they simply refer to how they show up in your DNA.  For the sake of simplicity, genes are expressed by alleles which can be written as being an uppercase (A) or lowercase (a) notation. Recessive refers to a gene being written as “aa” (homozygous recessive) or “AA” (homozygous dominant) or “Aa” (heterozygous dominant).
Through our exercise, the students found that they had a variety of similarities with their classmates–some that they had never thought of before! Chance plays a large role in genetics and it is through chance (such as genetic random mutations in our DNA) that causes diversity among us all. This lesson was an eye opener in showing us that there is always more than meets the eye.