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Alan Alda in Scientific American Frontiers


Photo Marzke

Dr. Mary Marzke, Professor of Anthropology at Arizona State University, received her AB (1959) and Ph.D. (1964) from the University of California Berkeley, and her M.A. from Columbia University (1961). Her research focuses on the evolution of the human hand and bipedality.

Marzke's work tests the hypothesis that prehistoric tool use and tool making were important factors in the evolution of our distinctively human hand and upright posture. Marzke monitors muscle use and hand movements during manufacture of prehistoric tools, observes manipulative behavior by apes, compares humans and apes in muscle mechanics and joint ranges of motion, and uses 3D techniques to measure bone and joint surface features that affect the hand's capabilities. This research suggests that the surface features of fossilized joints can now serve as clues to muscle mechanics, movement capabilities and potential manipulative behaviors of ancestral human species.

Her recent publications appear in the American Journal of Physical Anthropology and the International Journal of Primatology.


For links to this scientist's home page and other related infomation please see our resources page.

Marzke responds :

1.05.01 Shannon D. asked:
Do you think that tool-making abilities and planning strategies (cause and effect reasoning) evolved simultaneously or is the connection linear? Why hit upon tool making rather than, say, language? Tool-making ability seems to encompass more creatures than does language. So then why would we get the cause and effect reasoning from tool making, and not the apes and other creatures that use tools? Do any other primates or sea mammals use tools? What makes something a tool? Can a rock be a tool or does the tool have to be fashioned, hewn etc. in order to count as a tool?

Marzke's response:
These are all good questions. I think tool-making abilities and planning strategies were evolving simultaneously in our ancestors, but not necessarily in exclusive relationship to one another. Planning strategies are required for other behaviors such as foraging for food and predicting outcomes of social interactions, in many species. Manufacture of the earliest human stone tools would have required the ability to recognize the possible source of sharp flakes from stone cores and to anticipate the application of these flakes (or the sharp-edged cores) to the procurement of food. At the same time, the manufacture and use of these flakes and sharpened cores would have increased in effectiveness with the evolution of features in the hand that distinguish modern and ancestral humans from apes and monkeys. Neither the ability to make tools nor the ability to make them in anticipation of use elsewhere is unique to humans. For example, chimpanzees modify sticks in anticipation of their use as tools for retrieving insects at other locations. However, humans are distinctive in the nature and variety of tools they make, in the extent to which they have become dependent upon tools for survival, and in the evolution of anatomical features and aspects of the brain relating to tool-using and tool-making activities.

Tool use is more widespread among animals than tool making. Some birds, sea otters, and many primates use natural objects such as sticks and stones for tools.

1.05.01 Tina H. asked:
I'd like to know why you think there was an "intelligence explosion" around 50,000 years ago. Isn't this something of a chicken-or-egg argument? Don't you need a big, smart brain first to take advantage of the dexterous hands? How do you know it's the hands driving the brain's development and not the other way around?

Marzke's response:
This is a good question. In my view, the hand and brain of our ancestors evolved together in adaptation to both manipulative behavior and locomotion in the trees. As survival became increasingly dependent upon dexterous hands for holding on to small branches with one hand and retrieving fruits and insects with the other, there would have been selection for fine control of the hand by the brain. Evolutionary changes in the brain in turn would have allowed for a greater range of manipulative behaviors, and thus the evolution of one was a factor in the evolution of the other.

It is interesting that some modern human anatomical features that enhance tool-using activities (such as throwing stones and pounding nuts with stones) appear in fossil hands of human ancestors whose brains are still chimpanzee-like in their size relative to total body size. Chimpanzees use tools for these activities today, but the modern human features would have allowed our ancestors to perform these activities more effectively. Later, around two and a half million years ago, there is evidence of both larger brains and additional modern human features of the hand, as well as evidence that stones were not just used but were also made into more effective tools by our ancestors. From this time on, we see evidence for evolutionary changes in the hand, the brain, and the tools.

1.05.01 Tina V. asked:
I am interested in knowing more about the bipedalism issue. Is tool use a by product of bipedalism, or the reason for it?

Marzke's response:
I think tool use may have been an important factor in the origin of bipedal posture. We use our trunk as leverage for throwing objects like baseballs and stones, hitting objects with bats, clubs and axes, and for digging with tools. Rotating the trunk contributes to our ability to accelerate these tools, and thus increases their effectiveness. We have evidence from early fossil human ancestors that they had good balance on their hind limbs and would have been able to use the trunk as leverage in using natural objects such as stones, wood and bones as tools for throwing, clubbing and digging. Specializations in the locomotor apparatus for long distance walking appear to have come later in our evolution. Since our early human ancestors also had the ability to control the grip of stones by the thumb, index and middle fingers, they should have had an advantage over other ape-like primates in the ability to use these tools as protection against predators and for obtaining small game and underground foods.

Chimpanzees throw stones and wave sticks as part of their bipedal display activities, but they are unsteady on their hind limbs and do not have the acceleration or accuracy of humans in striking their targets. Differences in the structure of their hands and locomotor apparatus contribute to the differences from humans in the effectiveness of throwing and clubbing. I think our ancestors probably shared these chimpanzee display behaviors, which may have become increasingly advantageous as they became more habitually terrestrial. Anatomical features enhancing these behaviors thus would have been advantageous, and would have evolved as the behaviors contributed increasingly to survival.

1.05.01 Dr. John Spineti asked:
I farm in western Massachusetts. Over the past 50 years I have found many stone relics. Although I have found typical Indian arrowheads, some of the larger ones appear to be tools. My question is how can I verify this?

Marzke's response:
I would suggest taking your stone relics to an archaeologist at one of your Massachusetts universities. It is often difficult for the layman to distinguish stone tools from stones that have been chipped by rolling in streams or falling in landslides. However, the archaeologists have techniques for identifying marks resulting from human activities. It will be interesting if some of the stones you have found turn out to be elements of tool kits from earlier inhabitants of your region.

1.05.01 Linda asked:
I am trained as a dancer and as a dance notator and I found your study of how movement affected the way humans developed fascinating. I feel that my training as a dancer and movement analyst could be very beneficial in your field. Do you have any suggestions on what direction I should go in to explore the possibility of making a serious career change into your field of research? Thank you.

Marzke's response:
How wonderful to have a dancer's perspective on human movement! It is very helpful to students of human evolution to have an understanding of how our anatomical specializations are applied to our behavior. We have just begun an interdisciplinary graduate student-training program at Arizona State University that involves courses and research in subjects relating to musculoskeletal and neural adaptations in form and function. Students and faculty in physical anthropology, bioengineering and exercise science are working together to study human locomotion and manipulative behavior, from both a clinical and evolutionary perspective. This interdisciplinary approach allows students to learn a variety of techniques for recording and analyzing movements of humans and other animals, and for examining relationships between behavior and anatomy. I would suggest that you begin by reading an introductory textbook on physical anthropology to learn about the evolutionary questions we are addressing. If you think you would like to pursue the subject, you can look for a graduate program that provides training in physical anthropology as well as in biomechanics and functional anatomy.

1.05.01 Robert asked:
We were fascinated by the idea that the human hand has been shaped by selection for tool making. I was talking to my son about evolution and we wondered about early man: it seems that early man had to contend with many predators, all with physical abilities that were far greater than say "Lucy." Did early man already possess a greater intellect than any other creature? Or did the perils of the time force a natural selection for greater intellect? If the latter is true, we are truly connected to the creatures of our planet. Also, if my son wanted to pursue a career in your area of expertise, should he start with biology as a major in college?

Marzke's response:
"Lucy" had a brain that was approximately the size of a chimpanzee brain, relative to total body size. Studies of chimpanzees and other apes show that they have very sophisticated means of mapping their home ranges, anticipating locations of fruiting trees, applying the use of tools to food collection, and for developing and constantly adjusting strategies for maintaining complex social relationships. These abilities would have served our ape-like ancestors well as they applied them to their increasingly terrestrial life. As you say, they contended with many predators, as well as with competitors for food, and any anatomical features and aspects of the brain facilitating enhanced tool using and strategies for protection and food procurement would have been at the focus of selection.

Your son might be interested in taking an introductory course in physical anthropology, which would address these questions and others relating to human evolution. If he decides to pursue the subject, he could major in anthropology or in biology. The anthropology program would have the advantage of including the cultural as well as the biological aspects of contemporary and ancestral humans, whereas the biology program would give him better depth in the understanding of humans in the larger context of contemporary and ancestral animal species. Both majors would provide a good introduction to evolutionary theory.

1.05.01 Cynthia asked:
Is there any evidence of other primates using their physical capabilities for any sort of game-playing, throwing balls, etc - even if they can't hold a bat? Could this game-playing, if it exists, suggest possibilities of similar thought processes?

Marzke's response:
This is an interesting question. One of my most enjoyable experiences was the observation of chimpanzees at a captive colony in Texas. While my primary focus was manipulative behavior, I was constantly distracted by the games played by the juvenile animals. I remember one in particular, in which a chimpanzee had collected several sticks and had arranged them in a circle. He sat in the middle, looking as if he were very pleased with his new "house". Then another chimp came along and removed a stick. Chimp #1 tried to get it back, to no avail. Then a third chimp joined the game and distracted chimp #2 while chimp #1 retrieved the stick. The game of stealing, retrieving, and strategizing went on for a long time.

These kinds of thought processes are seen in many situations in captivity and in the wild. You might be interested in reading the book on chimpanzee politics by Frans DeWaal.

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