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Why facial muscles?
Now, this might seem a bit odd, but there are people who compare the muscles in faces of humans and animals.
Who are those people? Who would occupy himself with such a thing? They usually are evolutionary biologists and psychologists, and focus their work on facial expression, which is, very obviously, closely connected to muscles.
FACS
Ekman and Friesen published the Facial Action Coding System (FACS) in 1978, which is a very precise method of coding which muscles are active in a human face at a given point of time. Today this is commonly used for the interpretation of emotions, but was actually designed as a means to describe human facial expression (note: Ekman and colleages published a new version of the FACS in 2002). The FACS is, as Dr. Bridget Waller (Univ. of Portsmouth) pointed out, an “anatomical description tool”; not more, not less.
In order to make comparisons between non-human primates and humans, biologists started developing FACS for other species. As far as I know, the FACS for gibbons and chimpanzees are finished, and Bridget Waller, Katja Liebal and others are working on the maquaque FACS.
Human anatomy
The human face has 5 basic musles, which are essential for facial expression, and an additional 10 “non-basic” muscles.
The first thing to note is that there are actually huge differences within humans regarding those 10 non-basic muscles: some people lack non-basic muscles, and often they miss muscles in an asymetrical fashion, meaning a muscle is present on one side of the face, but not on the other. This could explain a big amount the variance of interindividuals differences in (subtle) facial expression. And, believe it or not, this was not known until a couple of years ago, maybe because – in the history of medicine – the necessity of examining facial muscle structure in corpses has rarely arisen.
Interspecies comparison of facial muscles
Another very interesting fact is this: there is a huge similarity between the facial muscles of chimps, gibbons, maquaques and humans. To quote Bridget Waller:
“It’s basically the same muscles over different facial bone structure”.
That does not mean, however, that we have (1) the same facial expressions as e.g. chimps. Neither does it mean that (2) the same expression between e.g. chimps and humans means the same thing
(1) Obviously, other species are doing things with their faces we don’t. And, in contrast, we do, too. Moreover, the oftentimes extremely different bone structure makes some of the facial expressions impossible.
(2) When a chimp shows his teeth, it looks to us like he’s smiling. This is a display of (deducted from ethological observation for many, many years) is fear/threat! Now, the FACS for other species obviously helps in coding what these animals do with their faces, but the meaning of it is something entirely different. I was told that different groups of the same species actually show different facial expressions, so there also seems to be a cultural, ontogenetical learning aspect involved.
Thanks for the inspiring lecture, Bridget!
A few words on animal treatment in this line of research:
I am very impressed. Bridget, Katja and their co-researchers care a lot about animals, and don’t get tired to point it out. There are two ways of identifying facial muscles reliably:
(1) Put a small electrode in it, and activate the muscle with a bit of electricity. In human research, this is done without painkillers, and with the person being awake. It doesn’t hurt, and the videos are ludicrous. For animals, they only do it when the animal is sedated (in order to be 100% sure that there is no pain involved), and since they don’t want to sedate animals for their research, it is done when the animals – once a year – are sedated for a standard medical examination.
(2) Post-mortem examinations. This was necessary for the human FACS, as is also necessary for other reliable tools regarding other species. This second point is actually the reason why the maquaque FACS will take some time, due to the lack of corpses. And trust me, if you see these researchers speak, you know they would rather make the research a couple of years longer, than have their maquaques die an early death.
