Question

Using the data in Table 2, answer Question 2 in the Lab Worksheet by graphing the Cranial Volume versus the Foramen Magnum Index for each skull. This should give you a total of five dots on the graph (one dot per skull). Label these dots to indicate which dot corresponds to each skull.

Table 2: Quantitative skull analysis data Character A. africanus H. erectus H. neanderthalensis Chimpanzee H. sapiens (Modern) Cranial width 11 14 17 13.5 15.5 Cranial length 12.5 11 16 12.5 15 Cranial height 7 14 15 7 13.5 88 127 106 108 103 Cranial Index 402 900 1703 1310 1310 18 19 21 22 18 Cranial Volume Total skull length Foramen Magnum distance to back of skull Foramen Magnum Index 4 5 5.5 2 5 22 26 26 9 27

Graph the Cranial Volume versus the FMI for each skull on Chart 1

Based on the data you obtained for the hominid skulls (in Tables 1 and 2 and in Chart 1), describe at least three major changes that have occurred in hominids over the last 2 million years.

Answer 1

Chart 1: Cranial Volume versus Foramen Magnum Index for hominid skulls 50 40 30 2 3 Foramen Magnum Index 20 10 4 0 500 1500 2000 1000 Cranial Volume 1-A.Africanus 2- H.Erectus 3- H.Neanderthalensis 4- Chimpanzee 5- H.Sapiens

Cranial capacity is a measure of the volume of the interior of the skull of those vertebrates who have a brain. The most commonly used unit of measure is the cubic centimetre (cm³).

Foramen magnum is the hole in the base of the skull through which the spinal cord passes.

Foramen magnum index (FMI) = transverse diameter/ antero-posterior diameter x100

Foramen magnum is an important landmark in the basal region of the cranium because through it significant vital structures transmits i.e. lower end of medulla oblongata along with meninges, vertebral arteries, and the spinal accessory nerve. The foramen magnum functions as a passage of the central nervous system through the skull connecting the brain with the spinal cord. On either side of the foramen magnum is an occipital condyle. These condyles form joints with the first cervical vertebra. This implies more active passage of nueral signals have been possible in modern humans.

Human/ape differences in the position and orientation of the foramen magnum reflect differences in habitual body posture and mode of locomotion. As early humans faced new environmental challenges and evolved bigger bodies, they evolved larger and more complex brains.

A.africanus brains started to show subtle changes in structure and shape as compared with apes. For instance, the neocortex had begun to expand, reorganizing its functions away from visual processing toward other regions of the brain. As our cultural and linguistic complexity, dietary needs and technological prowess took a significant leap forward at this stage, our brains grew to accommodate the changes. The shape changes we see accentuate the regions related to depth of planning, communication, problem solving and other more advanced cognitive functions.

Brain size increases slowly: From 6–2 million years ago

During this time period, early humans began to walk upright and make simple tools. Brain size increased, but only slightly.

Brain and body size increase: From 2 million–800,000 years ago

During this time period early humans spread around the globe, encountering many new environments on different continents. These challenges, along with an increase in body size, led to an increase in brain size.

Brain size increases rapidly: From 800,000–200,000 years ago

Human brain size evolved most rapidly during a time of dramatic climate change. Larger, more complex brains enabled early humans of this time period to interact with each other and with their surroundings in new and different ways. As the environment became more unpredictable, bigger brains helped our ancestors survive.

The modern human brain can:

- store many decades worth of information;

- collect and process information, then deliver output, in split seconds;

- solve problems and create abstract ideas and images.

It can also do much more.