Friday, December 21, 2012

eyes on the horizon

Horizontal pupil of a goat (

 Literature and lore often depict satanic or demonic animals as having hooves, horns, and elongate pupils. But my experience with goats, their delicious cheese and cute little tongues lapping up food at a petting zoo suggest otherwise. So I’m going to go ahead and make a bold statement: maybe these attributes are not markers of a demonic origin, but adaptations for predator avoidance and feeding.

You’ve probably noticed that livestock animals like horses and cows have horizontally rectangular pupils? Admittedly, this difference from our own eyes can make them seem unrelatable and a little spooky… probably interpreted as “demonic” by scribes of old. But look at the eyes of an animal, you can make inferences about where they spend most of their time, and what sort of predation they are likely to face.

Wide-angle view of ungulates, thanks to eyes being on
either side of the head and horizontally stretched pupils.
Ungulates (hoofed animals like deer, goats and sheep, bovine, horses, etc. that graze on grasses) all have the horizontal pupils, and eyes generally situated on either side of the head. This adaptation gives them an expanded range of peripheral vision. As grazers that must keep their heads down in open fields and grass plains, they have to be able to keep an eye on the horizon for Mufasa and Simba coming to eat their asses, even as they are munching on grass. Once motion is spotted, the zebra/sheep/antelope/whatever is equipped with long legs and speed that usually gets them out of hot water.
Reduced angle view that carnivores

The predators of these ungulates have vision adaptations of their own. Their eyes are situated more on the front of their head, causing the images seen by each eye to overlap. This is called binocular vision, and allows the animal keen depth perception fitting for a hunter. Of course, they trade wide-angle peripheral vision for their depth perception. But as predators and not prey, they don’t need to monitor the expansive horizons for danger as attentively. In addition, rounded pupils allow for super-tight focusing, perfect for spotting a tasty morsel off in the distance. Great depth perception + focusing power = zebra for dinner.

Can you think of any other animals with crazy eyes? Or eyes placed on the head differently than they are on yours? What do these things tell you about the animal's role in the food web?

Tuesday, December 18, 2012

try to b positive

Do you know your blood type? I do. Turns out, I’m a proud B positive. Representin’ homies.

A few years ago, I had my blood typed out of curiosity. They had to take three vials of blood to complete the test- which I initially found absurd. But when I stopped to think about how the blood typing system works, three vials made sense.

You’ve heard the blood types before: A, B, O, or AB with a positive or negative stuck on the end. What these letters really represent are proteins that belong to the ABO blood group. You see, on the surface of all your red blood cells are imbedded little proteins in the membrane. These are fittingly called- wait for it- surface proteins. They act like identity badges, marking the cell according to which protein floats in the cell membrane. Maybe you have A proteins, or B proteins, or both, or neither. If you have both, you are an “AB” blood type. If you have neither, you are an “O” blood type (O really stands for “none”). So, if you’re “A,” you are technically either “AA” or  “AO.” At the end of the day, you only have “A” proteins so you are just called an “A” bloodtype. Same thing goes for us B types.

There’s another category of surface proteins, known as the Rhesus blood group, or “rh” for short. If you have rhesus proteins, you are “rh-positive.” If you don’t, you are “rh-negative.” This is where the positive/negative part of your blood type comes from.

When blood transfusions take place, phlebotomists must make sure to not give blood with any proteins that the recipient does not originally have. For instance, if you were to give A positive blood to a B negative person, their body would be all “what are these B proteins?! And rh proteins?! Ah HELL no!” and attack those cells. Give that very same person A negative blood, and there’s no problem. Their body would not detect any proteins with which it was not already familiar.

With this knowledge, you can figure out that O negative blood would be accepted by anybody, since it has no proteins for a donor to reject. This is why O negative people are called “universal donors.” Conversely, AB+ blood may only be accepted by AB+ people, since it has all possible surface proteins that could cause a immune reaction. Likewise, AB+ people can accept any blood, since their bodies are already familiar with all three of the possible surface proteins. Ah lah, AB+ people are called “universal recipients.”

All of these proteins are inherited genetically. Each parent can contribute one protein of each category. An “AB” parent can contribute either their A or their B, while an O parent has nothing to offer. So, if Judy (O negative) and Bill (O negative) have a B positive child, Judy got some ‘splainin to do. Blood types were historically used as paternity tests, but as you can see, can sometimes be inconclusive. They are only able to rule out, not determine, a parent- and only part of the time at that.

Armed with the knowledge that there are three possible proteins that may determine a blood type, I understood why that vampire nurse bled me like a stuck pig when I went to get my blood typed. They needed one vial to test for A proteins, one to test for B proteins, and one to test for the rhesus group.

Do you know your blood type? Go find out. Then, I dare you to figure out all the possible blood types your parents could be. It’ll be so much fun!