Evidence for Evolution – Chicken ‘Arms’
It’s all about coloring vertebrate fore limbs, harking back to the famous Dog Day where we started the comparison of tetrapod limbs to find the underlying similarity of humerus, radius & ulna, carpels and 5 digits.
On Monday, students applied their learning about homologous structures to finding their way around chicken wings from the meat counter at the supermarket.
I’ve learned to demo dissections first, instead of relying on the total discovery method. I just can’t stand the chaos and the kids don’t really like the uncertainty of what they are trying to find. Ends up with lots of random hacking and throwing bits of meat around… Yes, direct instruction.
Have them all find the parts of the chicken wing by pointing to them on their own arms. Shoulder, elbow and thumb, to get them orientated. Then show how to make longitudinal incisions using the forceps to pull up the skin and slide the scissor point under, parallel to the muscles so I don’t accidentally snip any other structures. Just like a surgeon. And how to snip at the connective tissue to free the skin from the underlying structures.
Show parts and ask them to find them/identify them from the camera image of my dissection. Most fun is to pull the silvery tendons and make the wing ‘hand’ wave. They can do this with by pushing down on their own wrist tendons.
Emphasize that they TAKE TURNS with the forceps and scissors (like a knife and fork) – one does the humerus dissection, then change over and the other does the lower arm dissection. (They have a tendency to share the work with one on the scissors and one with the forceps.)
Assessed them for being on task and following directions during the dissection. That really helps keep things calm and focused. Next day, assessed their biological drawings. Many are still drawing what they THINK they see, or SHOULD see, and not what they actually see.
Had some contagious hysteria in 7th period – one girl felt sick and dizzy, then about 6 more did. My line is if you eat chicken, you should dissect it. Or give up eating chicken! Really pushed meat eaters to stay, but not cruelly.
Next day, had kids model exactly how bird wings map to ours, and how we would fly, if we were birds – sort of the point of the whole thing: