Homo habilis

Homo habilis

Study Question:
Homo habilis seems to be the best candidate for the first stone tool maker. If this species was the first to manufacture stone tools it would have done so for perhaps hundreds of thousands of years. What sort of morphological changes in its bone structure might we expect to have evolved to suit this behaviour? Can you suggest some analysis that we could carry out on habilis skeletal remains that might detect such morphological changes? Consider how you might compare habilene skeletal morphology to earlier hominids, who we know didn’t make stone tools, and later hominins who we know did.
ANSWER:

There are several important changes that we would want to look for in the bones of the earliest stone tool makers. First, we would want to look at the structure of the hands and feet. The feet would have to show evidence of complete bipedalism so that the hands would be free to develop into structures specialized for behaviours other than walking. Foot markers would include the alignment of the hallux and the shape of the longitudinal and transverse arches. Additionally, we would need to look for other markers of bipedalism such as the location of the central foramen and the shape of the superior nuchal line and occipital condyles of the cranium. Then, we would want to look at the hands. They would have to show evidence of increased dexterity such as the apical tuft on the distal phalanges of all five digits and the development of the insertions of various tendons.
As well as looking at the bones, we would want to analyze the chemical composition of the bones themselves. This can tell us a lot about the diet of the individual. One theory for the evolution that allowed for the development of stone tools is that it allowed our ancestors access to more meat, and meat is a much more calorie dense food source than plants. Organisms that eat a lot more meat have higher nitrogen levels in their bones. This makes sense considering meat is made up of amino acids which have a nitrogen-containing amine group attached to their central carbon (a-carbon). By analyzing the chemical makeup of bones, we can see which organisms had access to more meet and therefore which species was able to make stone tools. The earliest evidence of increased nitrogen in the bones would correspond to the earliest stone tools.

 

Musings:

1) Recall from the lecture on Evolution and Natural Selection that Evolutionary Biologists are unsure whether the process of evolution occurs via very gradual, incremental changes, as was traditionally thought, or whether it occurs via relatively rapid, major changes; Punctuated Equilibrium. If it occurs as slow incremental changes would it be reasonable to expect a new genus Homo to suddenly appear? The idea that, within the hominin line, there might have suddenly evolved a brand new genus fits better with the idea of Punctuated Equilibrium. However, also keep in mind that not all the remains of individuals of a species will end up as fossils for us to discover. In fact, it is likely that a very, very small percentage ever become fossils and an even smaller percentage survive buried in sediments long enough for us to dig them up. Since we are never going to find example fossils of every stage along the evolutionary history of a genus, it is not surprising that we seem to find the remains of individuals that are significantly different from related individuals that date to an immediately preceding time period. Do you think the early species of Homo that we have discovered so far (habilis and rudolfensis) are good examples of Punctuated Equilibrium? If they are, can you think of any characteristic(s) of these species that might explain such a sudden, major change in hominin morphology?

 

2) This section more than any other in the course deals with those traits that we traditionally see as what define us as ‘human’: large, complex brains and their associated intellectual capabilities; walking erect on our legs, and hairlessness. (Some might also add culture as a defining trait, although by any anthropological definition of culture, chimpanzees and bonobos share this trait.) Among physical anthropologists and paleoanthropologists there is no set criteria for the use of the term ‘human’; no definition has ever been put forward for it within the sciences, and different researchers seem to apply it differently. That is, they seem to draw the line between what they would consider “human” and what they would consider “pre-human” at different places in our evolutionary history. Some researchers would include Australopithecines in the ‘human’ category, while others don’t even include our closest cousins, the Neandertals, as ‘humans’. The Oxford English Dictionary defines a ‘human’ as a member of the species Homo sapiens, but since there is constantly significant debate among physical anthropologists and paleoanthropologists (who are the ones who ultimately define the taxon Homo sapiens) this dictionary definition is essentially meaningless. In this light, where would you draw the line between human and non-human?

Because we don’t have a good working definition for the term ‘human’ this is an entirely subjective exercise – there is no right answer but it tends to indicate either your approach to classifying things, or your view on the importance of distinguishing humans from the rest of the animal kingdom.

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