HL 2 Biology

D.3b: Hominid Evolution

<<Hominid Evolution>>

  • Humans categorized as primates because:
    • opposable thumbs and toes
    • fingernails
    • forward facing eyes
    • rotatable shoulder joints
    • color vision

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Hominid Skull Comparison (p.319)

1) Diameter; 14cm. The volume= 4/3(π)(r^3) =  1436cm^3

2) Although a change in cranial capacity does not necessarily imply greater intelligence, but significant changes would require dietary changes. The change in the diet may suggest that humans evolved to consume different nutrients and resources that differed to those of apes. Thus, their cranial capacity is seen to be contrasting to that of the apes.

3) Looking at the degree of prognathism, the skulls of (a) and (b) can be seen to contrast with each other. Skull (a) consists of a more narrow jaw line compared to that of skull (b).

4) It is evident that the sagittal crests found in (b) is flatter than (a). As the sagittal crest is flatter, the jaw is seen to be lower in position and larger. The sagittal crest may function to help ease the consumption of food by helping to break down and chew on the resources.

5) In skull (a) the brow ridges are more distinct as it seems to be greater than that of skull (b). The brow ridges are not clearly apparent on the skull (b) compared to that of skull (a).

6 a) Table 1: The Comparison between Skull (a) and (b)’s teeth

Screen shot 2013-09-23 at 8.14.11 AM

b) Molars are functioned to help us consume our food more easily as we chew the resources down. It is related to diet because it can determine what types of food people can consume, depending on the size of the molars. As humans, our molars have evolved to become more smaller as we started to obtain food in smaller pieces.

7) Skull (b) is more round than skull (a) and more wide in surface area. The nose  is centered in the frontal lobe of the brain.

8) The foramen ovale is one of the larger holes that transmits nerves, but cannot be observed closely as it is located inside of the skull. For humans, it is located in the center whereas for cats/dogs, the foramen ovale is located in the back. The significance of this position is possibly that cats/dogs do not use their brains as much as humans.

9) The rotatable shoulder joint enables humans to move their arms freely unlike the cats and dogs.

10) Skull (a) consists of a more smaller angle as it’s jaw is more slanted down compared to skull (b) with a more flattened jaw positioning enabling a smaller jaw angle to form. As the angle is greater, then it may help the jaw to generate more force. The jaw angle is related to the diet since in the early hominids, the jaw size was larger which indicates that their main diet was vegetarian. Possibly the more hard texture of the vegetables and such resources enabled them to consist of a larger jaw angle to generate much force. Yet the jaw size decreased over time as the hominids evolved, increasing meat into their diet. Less force may have been needed for the consumption of meat, compared to the vegetarian diet in the early hominids. Thus, as the diet of these organisms evolved into a more meat based diet, the jaw angle decreased as well as the amount of generated force.

11) I hypothesize that in the course of the hominid evolution, the pelvis, backbone and rib cage will become more firm, smaller and wider. The backbone may become more up straight as the hominids evolved to pick resources off of trees, and their walking stance of standing up on two feet. As the backbone becomes more straight, its relative size may decrease as the hominids no longer need to walk, hunched back.  Also, their pelvis will evolve with this and become shorter and wider, as the body becomes more firmly stable when standing up right. The change in this pelvis enable the hominids to walk and run up right on two feet, as their knees become tucked inside. The rib cage may also reduce in size in balance with the backbone.

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