Where did we come from? - Part II

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Go back to Part 1. Or continue anyway, I'll give you a quick recap. *Free*

If you have stayed with me through Part 1, I assure you, things are going to get easier now. One big reason is, we're now zooming in closer from all life to our particular species and it will be a lot easier to relate to whatever the classification system describes to us.

Colored words in each list show where we fall. The bottom bar reminds you of the important stuff, so you don't need to memorize anything. It also acts as sort of a progress bar which shows how deep we have reached in the classification system so far in the post.


This is where we left the last post at, and for a quick recap let's remind ourselves that thank god, we belong to the:
  • Domain Eukaryota : I can't be too sure, but I'd miss my nucleus, mitochondria and a bunch of other stuff that doesn't exist in prokaryotes
  • Kingdom Animalia : the other options were to be a plant, a fungus, a protist, or a moneran. And I don't even know what the last two mean, so I have a feeling I wouldn't quite fit in
  • Phylum Chordata : The criteria for being a chordate are 
    • pharyngeal slits (often used as gills)
    • dorsal nerve cord (a bunch of fibers that connects our brain to the organs)
    • notochord (a rod that supports the nerve cord, I think this is where our spinal cord came from)
    • post-anal tail (no comments)

      Now I admit none of this sounds super-important to all of us right away, but these are some of  the major reasons why we are the way we are.
Moving on to the next levels of the classification system:




This is where the "Hey, I've heard that before!" or the "I know that already <smug feeling>" begin.

Among the 3 subphyla that comprise the Phylum Chordata, we belong to Vertebrata. The vertebrates all have a backbone and the brain is protected by a 'cranium' or a skull. In most people's head, vertebrates = animals, but they're forgetting something called tunicates/urochordates (sea squirts, sea tulips) and the lancelets/cephalochordates (which are even commercially harvested in certain parts of Asia as a food item). We currently think that the vertebrates emerged from a cephalochordate ancestor. However, I'm not feeling special knowing that there are about 50,000 species of vertebrates.

The next step is dividing the Vertebrates into various Classes. The first half of the list is largely unheard of (except maybe in a Paleontology class), but the last 4 are pretty evident if you've read any high-school level Science. Mammals are pretty advanced animals with a four-chambered heart, a well-developed brain (well, for some of us at least!) and four limbs. Our USP lies in our hair (never thought I'd say that!) and our mammary glands (and not where they're housed, stop grinning).

A few cool facts while we're on the topic:
  • Mammals originated sometime in the Jurassic (an interval of time from 200 million years ago to145 million years ago). And we're still around so I think it's a bit unfair that everyone focuses on the dinosaurs in the movie.
  • The dinosaurs were wiped out by an event called the Cretaceous-Paleogene extinction event. Before the event, the dinosaurs were the cool kids/bullies of the block, but right after the event, the underdogs (mammals) boomed.
Anyhow, we're still one of about 4500 "advanced" species of mammals, which is better than the 50,000 stat at the previous level, but I'm not satisfied.



The Class Mammalia has 3 subclasses: the Monotremes lay eggs (eg, platypus), the Marsupials rear their kids in an external pouch (eg, kangaroo) and the Eutherian kids develop inside the mother's placenta. We're among 4000 species of mammals with a beautiful mother-child connection and others include dogs, cats, horses, sheep, elephants and whales.

The Eutherians that diverge into several weird sounding names, and suffice it to say, we belong to the Order Primates. Primates have a lot of brilliant features, some of which are:
  • We're said to have relatively large and complex brains (though I'm convinced that the loophole is "relatively" because I'm somehow not convinced this applies to everyone around me)
  • Our forward facing eyes have overlapping fields of view and this is what allows us a perception of depth (students of Remote Sensing will know this is also the basis of Stereoscopy)
  • We have grasping hands, with opposable thumbs, and flat nails as opposed to claws (this is what allows us to hold our beer mugs comfortably)
  • We have collarbones (which can be surprisingly aesthetic on some humans of the opposite sex)

We narrow down our own lineage from the ~350 species of Primates to the ~280 advanced primate species called the Haplorrhines. Totally irrelevant, but the primitive species include the lemurs and the Aye-aye. Very relevant, the words "Haplorrhines" and "Strepsirrhines" refer to "dry-nose" and "wet-nose" respectively. Although wet-nose does not seem too glamorous, we the dry-nose-primates don't quite have the same smelling-powers as the wet-nose-primates. Not sure if that's a good thing or bad.

A significant jump of exclusivity comes at the Superfamily level where the advanced primates are divided into four groups: the tarsiers, two groups of monkeys, and the apes. A lot of interesting points at this juncture:
  • Tarsiers are mostly nocturnal and live in Malaysia, Indonesia and the Philippines.
  • The New World monkeys are mostly tree dwellers found in Central and South America. Some examples are howler monkeys and spider monkeys.
  • The Old World monkeys include tree dwellers and terrestrial species (those who live fully or partly on the ground). These are found in Africa, Asia and some parts of Europe.
  • We're not monkeys, though yes, we are related to them. But then again, technically, we are also related to horses, toads and sparrows. We are more closely related to the monkeys than to horses or toads or sparrows, but we are even more closely related to the other apes. So seriously, if scientists had their way, I doubt if calling someone a monkey would still be a popular jibe.
  • There are about 20 species of Apes and all of these, belonging to the Superfamily Hominoideae, are called hominoids. We're all apes, and thanks to this, we have the luxury of rotating our arms and not having a tail to groom as well.
  • We're more closely related to the Old World Monkeys than the New World Monkeys, and if you consider the fact that the former also occupy land and so do we, it'll seem more logical and you'll have a "Oh, yeah, of course!" moment.


 

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