Question

Homo: The Humans

During the Pliocene-Pleistocene transition the Homo genus appeared in the fossil record. The Homo genus is a a continuation of the Gracile Australopithecines. Like those that came before, Homo is an obligate biped, but unlike its precursors Homo displays a unique set of physical adaptations along with behaviors that make the genus unique among hominins. To begin with, Homo and all its eventual lineages display hunting behaviors along with the associated stone tools necessary to process meat. At the same time, the creation and dependence on stone tools and other cultural technologies is a function of the increase in brain size that begins with the onset of Homo.

Hunting, the new Homo subsistence pattern, required not just a new kind of mind set to create new cultural technologies but at the same time required a specialized hand that would allow for better manipulation of objects while being capable of resisting the unique physical pressures associated with making tools.

In addition, being able to run after prey became essential. The Homo genus was the first to display adaptations that allow for endurance running. The type of running that Homo becomes known for is not a type of running that allows us to be fast but rather it allows us to run for long distances at a pace which forces prey to undergo hyperthermia over the long run.  

Your task for this activity will be to compare and contrast the locomotor features of Australopithecus afarensis to Homo erectus. You will accomplish this by answering the following.

Before you begin make sure view all relevant reading material so that you can give me informed opinions.

What anatomical features makes it possible for Homo erectus to be a biped runner.

Pick only one feature discussed in this week's material that allowed Homo erectus to be a biped runner.  

How is your chosen feature different from Australopithecus aferensis equivalent feature? Briefly explain the difference.

Lastly, I would like you to briefly explain in your own words how endurance running would enhance the fitness of the Homo genus.

Answer 1

Locomotor features of Australopithecus afarensis and Homo erectus:

Many research has been conducted for studying the postcranial skeleton of Australopithecus afarensis from the Hadar Formation, Ethiopia, and the footprints from the Laetoli Beds of northern Tanzania, are analyzed with the goal of determining (1) the extent to which this ancient hominid practiced forms of locomotion other than terrestrial bipedality, and (2) whether or not the terrestrial bipedalism of A. afarensis was notably different from that of Homo erectus.

It is demonstrated that A. afarensis possessed anatomic characteristics that indicate a significant adaptation for movement in the trees. Other structural features point to a mode of terrestrial bipedality that involved less extension at the hip and knee than occurs in Homo erectus, and only limited transfer of weight onto the medial part of the ball of the foot, which is not suitable for long distance running.

Biped running in Homo erectus:

Increase in body size, brain mass, post cranial modifications and upright posture of Homo erectus was the significant anatomical difference from A.afarensis which enables the Homo genus for long distance running.

And more recent theories suggested that bipedal locomotion was related to environmental factors which led to the advent of distinctive and remarkable anatomical features for a form of locomotion that is more energy-economic than quadrupedal locomotion. These anatomic features and adaptations include; adjustments to the general body architectural plan, in addition to cranial and postcranial modifications. Postcranial modifications are debated to be the most critical for a stable and fuel-efficient upright walking, other anatomic adaptation were complimentary. The most significant of these anatomical changes took place post-cranially particularly at the level of the pelvis, at the iliac blades. The blades have rotated along the sagittal axis for each, thus repositioning the anterior glutei muscles more anteriorly, while the gluteus maximus muscle was fixed posteriorly to persist as the most powerful extensor muscle of the coxo femoral joint, thus preventing the body from pitching forward during upright posture and during walking, and finally the anterior iliac spines became robust, for anchorage of sartorius and rectus femoris, which enables these two muscles to act as strong flexors of the thigh which is ideal for biped locomotion of Homo erectus.

Endurance running in fitness of Homo erectus:

Endurance is about sustained exercise with repetition and this combination makes for a healthy heart. When we run our muscles ask for more oxygen and we ask our heart to pump more oxygen carrying blood to them. Our heart then increases the number of beats per minute and pushes out more blood with each stroke than it would otherwise. Cardiac output is increased.

Over time our heart adapts and finds it easier to pump out more blood with each stroke, our heart rate comes down, as it doesn't need to beat as often to send the blood around the body, and the level of oxygen reaching the cells increases rapidly thus avoiding the level of stress in cells and improves the overall muscle fitness of Homo genus.