Primates

This post, and the post after, are mainly going to be about how humans are classified. I wrote a bit about this in my first post on human biology, but this post is going to go into more detail.

Our Phylum: Chordata

We're classified into "chordata" due to the presence of several characteristics:

• In the embryonic stage, we have a notochord, which is eventually replaced by a bony vertebral column.
• We have a dorsal (meaning "on the back") hollow nerve chord. The upper part forms our brain, while the rest forms the spinal cord.
• In the early embryonic stage, we have gill slits (pharyngeal pouches), but these disappear very early on.
• Embyros also have a postanal tail which also disappears during embryonic development.

Our Class: Mammalia

Here are the characteristics of mammals, which you probably already know:

• Hair
• Homoiothermic (maintain a constant body temperature)
• A four-chambered heart
• Development of the young within the uterus (i.e. mammals don't lay eggs)
• Babies drink milk from the mother's mammary glands

Our Order: Primates

The class Mammalia consists of a bunch of other orders, most of which are set apart by their distinguishing features: for example, members of the order Rodentia have chisel-like incisor teeth, and members of the order Carnivora have strong jaws with enlarged canine teeth. The order we're in, however is the primates, which are sometimes said to be distinguished by their lack of distinguishing features. A lot of the characteristics shared by primates are also shared by animals from other orders, but only the primates have all of the characteristics that I'm about to list off:

1. An unspecialised mammalian body. The primates' descendants are thought to be arboreal (live in trees), which may account for arboreal adaptations of primates and their generalised body structure.
2. Limbs that are unspecialised in structure, and are pentadactyl (five mobile digits on each limb) and have opposable first digits. Opposability of thumbs and big toes vary from species to species (for example we don't have opposable big toes, but we have very opposable- if that's even the right way of describing it- thumbs).
3. Nails instead of claws. This allows primates' fingers to be prehensile (capable of grasping). Additionally, primates have friction ridges, or fingerprints, to increase friction between fingers and objects.
4. Forward-facing eyes, allowing stereoscopic or three-dimensional vision. This allows fields of vision to overlap, which allows for more accurate judging of distances. The overall field of view is much smaller, but this is compensated by a highly mobile head and neck. Most primates have both rods (important for vision in dim light) and cones (important for fine visual discrimination and colour vision) in their retinas, though nocturnal animals may only have rods. The size of the brain concerned with interpretation of visual information is also relatively large.
5. Less keen sense of smell or olfaction compared to other animals. The length of the snout is also reduced, leading to flatter faces and more efficient stereoscopic vision.
6. Four incisors in both the upper and lower jaw, as well as canines, premolars and molars.
7. The part of the brain responsible for complex functions is relatively large, particularly the outer region called the cerebral cortex. The cerebral cortex is concerned with so-called "higher functions," including vision, memory, reasoning and manipulative ability.
8. Primates have differences in reproductive structures and behaviour as compared to other animals. Most are not limited to a specific reproductive season, but most only have one child at a time. Additionally, this child takes a long time to grow and mature, and requires a lot of parental care, restricting the number of children that primates have.

Primates are then divided into three main suborders: prosimians, tarsiers and anthropoids. The prosimians include lemurs, lorises, pottos and galagos. Tarsiers only contain tarsiers, while the anthropoids include monkeys, apes and humans. The prosimians are generally considered to be more primitive and are called the "lower primates," while the anthropoids are considered to be the "higher primates." Personally, I think that's rather elitist of us. Lemurs are quite lovely creatures.

Now I've reached the point in the book where the authors have decided to go on about examples of different animals within each suborder. I'm not going to discuss this part, because to be honest, I'm not that interested at this point in time. If you're interested in the other kinds of primates, LEARN ABOUT THEM YERSELF. Tomorrow, however, I will be talking a little bit about apes and monkeys, though mainly only to discuss the differences between them and us. And then I'll have farmed all the crap I can out of this book, and I'll have to find some other way to spend the rest of my gap year. w00t!