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Human evolution
Skull
| Term | Definition |
|---|---|
| Cranium | The part of the skull that encloses the brain and protects it from injury. |
| Brow ridge | Bony ridges above and around the eyes. They protect the eyes from the powerful forces developed during chewing and biting. |
| Canines | Large, pointed teeth used for holding and killing prey, as weapons or for aggressive display |
| Zygomatic arch | Important muscles used for chewing pass through this arch in the 'cheekbone"'. The muscles are attached to the mandible and skull. |
| Nuchal crest | Extension of the skull to which the neck muscles attach. These muscles position, move and stabilize the head and cervical vertebrae |
| Sagittal crest | A ridge of bone running lengthwise along the midline of the top of the skull. Strong jaw muscles attached to it. |
| Molars & premolars | Large flat teeth that shear and crush food during chewing. |
| Foramen magnum | A large hole at the base of the skull through which the spinal cord and spinal arteries enter the skull. |
| Diastema | Space between the teeth for large canine teeth to fit into So that other teeth can come together. |
| Prognathism | When the lower portion of the face markedly projects forward. |
| Opposability of hallux (big toe) for humans and chimpanzees (which is present/absent, and why) | Human absent: Provides efficient toe-initiated push-off for propulsion Chimpanzees present: Divergent hallux allows grasping during tree-climbing |
| Longitudinal arches in foot for humans and chimp (which is present/absent, and why) | Human present: humans can push of ground with toes. Chimp absent walks flat-footed, however this is not the dominant method of locomotion. |
| Robustness of heel bones for humans and chimp (comparative) | Humans: Heel bones are larger and stronger to absorb heel-strike forces and provide balance during upright standing. Chimpanzees: Heel bones are smaller and denser, serving as attachment points for muscles and ligaments used in climbing |
| Orientation of foramen magnum for humans and chimps | Humans: central and downward opening, head balanced on top of the spine, so less neck muscles support needed. Chimps: Towards rear of skull and angled backwards, to position the head forward of the spine when walking quadrupedally. |
| Shape of Spine for human and chimps | Humans: S shaped (two curves) to position the center of gravity directly above the feet, to absorb shock and provide flexibility Chimps: C shaped, weight of abdomen well supported on C-shaped spine arches while on four limbs |
| Shape of rib cage | Humans - barrel allows the arms to be swung from side to side during bipedal locomotion. Chimps - Cone, contains the relatively large gut and allows wide range of arm motion for brachiation. |
| Shape of pelvis | Humans - Shorter broader, bowl shaped, (supports the gut when upright (with weight over the feet) and allows for a smooth gait Chimps - Narrower, flatter, more elongated |
| Angle of femur | Humans - Angled inwards valgus < 90 degrees, places feet directly below the center of gravity as knee joints are closer to the mid-line than the hips. Chimps - Parallel femur valgus ~ 90 degrees, Knee directly below the hip giving stability when walkin |
| Size of femoral head | Humans - Larger, Increased ability to tolerate weight transfer and better stability when bipedal. Chimps - Smaller, Weight spread across all four limbs when walking quadrupedally or not at all when brachiating |
| length of femur | Humans - Longer, A longer lever so more efficient bipedal locomotion. Chimps - Shorter, A shorter stride, even when upright/bipedal. |
| Sagittal Crest | Humans - Absent, reduced jaw muscles mean no crest is necessary. Chimps - Present, the substantial jaw muscles needed to move the A large, robust mandible is attached here. |
| Relative size of the canines | Humans - Smaller, Humans use less overt displays (e.g. language, vocalizations) during aggressive interactions Chimps - Larger, used to display dominance and aggression (particularly in males) |
| Jaw | Humans - V-shaped no chin Simian shelf, larger jaw and muscles reflecting Chimps - U-shaped protruding chin. No simian shelf, because lighter as more meat was included in the diet and fire was used to cook and soften food and muscles reflecting largely |
| Freeing of hands advantage for bipedal | 🖐 Freeing the Hands Bipedalism allowed early hominins to use their hands for carrying tools, food, and weapons. This supported group survival and increased reproductive success by helping mates and offspring. |
| Thermoregulation advantage for bipedal | ☀️ Thermoregulation Standing upright reduced heat absorption and improved cooling through exposure to air currents. This helped bipeds travel further with less water loss, even in partly shaded habitats. |
| Energy Efficiency advantage for bipedal | ⚡ Energy Efficiency Walking on two legs used less energy than knuckle-walking. This made foraging more efficient and allowed longer travel with lower energy costs. |
| Predator avoidance advantage for bipedal | 🦁 Predator Avoidance Bipedalism helped early hominins spot predators over tall grass, improving survival. However, standing upright may have also made them more visible to predators. |
| Spinal stress disadvantage for bipedal | Spinal stress: Upright posture puts pressure on the spine, increasing risk of back pain and injury. Forces also affect knees, ankles, and feet. |
| Birth complications disadvantage for bipedal | Birth complications: Bipedalism led to a narrower pelvis, while larger brains required a wider birth canal. This evolutionary trade-off makes human childbirth more difficult. |
| Obstetrical dilemma | The obstetrical dilemma is the evolutionary conflict between walking upright and giving birth. Bipedalism needs a narrow pelvis for efficient movement, but bigger brains need a wider birth canal. This makes human childbirth more difficult. |
| cranial capacity | Over time, hominin brain size grew from ~400 cm³ to ~1350 cm³. Bigger brains need more energy, supported by meat-rich diets. This led to better tools, hunting, and language in a feedback loop of brain growth and survival. |
| Positive feedback loop | A cycle where one change reinforces another. In human evolution, brain growth led to better tools, hunting, and language improving survival and nutrition, which supported further brain growth. |
| Relative size of cranium | Braincase size increased over time, showing larger brain capacity and intelligence in later hominins. |
| Sagittal crest | Reduced and disappeared as chewing muscles became smaller with a softer, cooked diet. |
| Slope of forehead | Became more vertical as the jaw and teeth became smaller and the braincase larger. |
| Brow ridge | Moved to a central position under the skull, showing upright, bipedal posture. |
| Slope of face | The slope of the human face refers to the degree of forward projection (prognathism) or flattening of the facial skeleton relative to the cranial base. It is a key metric in physical anthropology and evolutionary biology that captures how the midface (nos |
| Foramen magnum location | Moved to a central position under the skull, showing upright, bipedal posture. (in the occipital bone, and forms around the base of the brainstem (the medulla oblongata), separating the brain above from the spinal cord below.) |
| Presence of diastema | The gap between teeth disappeared as canines became smaller and less used for aggression. |
| Degree of prognathism | The face became flatter and less protruding as jaw and teeth size decreased. |
| Shape of chin | Pointed chin appeared only in Homo sapiens, supporting a lighter jaw. |
| Size and shape of mandible | Jaws became smaller and less robust as diet softened, and tools replaced heavy chewing. |
| Presence of nuchal crest | Reduced and disappeared as head posture became upright and less muscle support was needed. |
| Curvature of dental arcade | Changed from a V-shape to a U-shape as jaws shortened. |
| Shape of incisors | Became smaller and more vertical over time. |
| Relative size of canines | Decreased over time as diet and social behavior changed. |
| Shape of canine teeth | Became less pointed and more blade-like for cutting rather than tearing. |
| Relative size of molars | Became smaller as the diet shifted from tough plant material to softer, cooked foods. |
Created by:
Carl.zo
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