User:Eberhard.27/sandbox

Research Topic:
The evolution in primates (primarily lesser and greater apes) away from brachiation and towards knuckle walking, and eventually bipedalism. Adaptations and changes that occurred in the shoulders, wrist, elbows, and hands of primates who utilized knuckle walking over bipedalism may shed light on to how or why knuckle walking evolved in to bipedalism. How did brachiation lead to the evolution of knuckle walking, and how did that later lead to bipedalism as the primary form of locomotion? What are adaptations needed for this to occur (anatomically) and how are these forms of locomotion advantageous or disadvantageous?

Annotated Bibliography

Kikuchi, Yasuhiro, Hironori Takemoto, and Akio Kuraoka. "Relationship between Humeral Geometry and Shoulder Muscle Power among Suspensory, Knuckle walking, and Digitigrade⁄palmigrade Quadrupedal Primates." Journal of Anatomy 220 (2011): 29-41. Onlinelibrary.wiley.com. Onlinelibrary.wiley.com, 4 Nov. 2011. Web. 11 Sept. 2014.

This article researches the affects of different types of locomotion on the arms of primates. The types of locomotion studied were quadrupedalism, knuckle walking, and brachiation. Not only does this study reveal general anatomical differences between primates, it also reveals the differences specifically due to their locomotive patterns, like how much stress is put on certain muscles due to movement, for example. These results help explain how the body evolved to both fight gravitational forces on the joints and move about more effectively.

Kivell, Tracy L., Anna P. Barros, and Jeroen B. Smaers. "Different Evolutionary	Pathways Underlie the Morphology of Wrist Bones in Hominoids." National Center for Biotechnology Information. U.S. National Library of Medicine, 23 Oct. 2013. Web. 14 Sept. 2014. .

The evolution of the wrist is a key to understanding the evolution away from brachiation and towards knuckle walking. Specifically studying the wrist bones of different hominoids shows that the wrist bone has experienced different evolutionary processes that cause a wide variety throughout primates, which can result in parallel evolution in some cases. For example, this study reveals that certain aspects of early human wrists evolved similarly to Gorillas, but not other great apes like Bonobos.

Kivell, Tracy L., and Daniel Schmitt. "Independent Evolution of Knuckle-walking in African Apes Shows That Humans Did Not Evolve from a Knuckle-walking	Ancestor." US National Library of Medicine. National Institutes of Health, 10	Aug. 2009. Web. 11 Sept. 2014.

While it is still unclear as to what type of locomotion human ancestors practiced, a widely believed hypothesis is that humans evolved from a knuckle walking ancestor. However, this study examines the hand and wrist configuration of primates to show that not all aspects assumed to be vital to knuckle walking are present in knuckle walking apes. Human hands and wrists were mainly assessed on their ability to possibly knuckle walk, but apes were not compared with these features. The evidence presented suggests that humans did not evolve from a knuckle walking ancestor.

Matarazzo, Stacey Ann, "Knuckle-Walking Signal in the Manual Phalanges and Metacarpals of the Great Apes (Pan and Gorilla)" (2013). Dissertations. Paper 755.

Knuckle walking requires adaptations in the hands and fingers of primates that can be different from species to species, but share similar aspects that act as a sign that an organism is capable of or was a knuckle walker. This dissertation examines if there are any differences between Pan and Gorilla in how they walk and their anatomy. This emphasizes the idea that certain aspects of knuckle walking can evolve differently or parallel, depending on the conditions. For example, curvature in the phalanges provide insight to how knuckle walking evolved due to both the degree of curvature and the amount of pressure put on each phalange when walking.

Richmond, Brian G., and David S. Strait. "Evidence That Humans Evolved from a Knuckle Walking Ancestor." Nature Magazine 404 (2000): 382-85. Nature.com. Nature.com, 23 Mar. 2000. Web. 11 Sept. 2014. .

Wrist morphology in early humans and apes seems to be an important area	to study when determining the evolution of bipedalism, which is asserted in this paper to be evolving from knuckle walking. Evidence is shown with research that wrist structure in early human fossils differs from those found later and also from primates who do not utilize knuckle walking. This	suggests that knuckle walking is a feature associated with the African Apes as well as early humans, which also suggests that humans evolved from a terrestrial ancestor that already used knuckle walking as a form of locomotion.

due Oct. 1st
https://en.wikipedia.org/wiki/Knuckle-walking

Edit made is last sentence in the "Advantages" section and is as follows:

African apes most likely diverged from ancestral orangutans who were adapted to distribute their weight among tree branches and forest canopies. Adjustments made for terrestrial locomotion early on may have involved fist-walking, later evolving into knuckle-walking.

 Citation 

Tuttle, RH. (2005). "Knuckle-Walking and the evolution of hominoid hands". American Journal of Physical Anthropology 26 (2): 171–206. doi:10.1002/ajpa.1330260207

 Suggestions 

1.)	Differences in knuckle walking methods in Chimpanzees and Gorillas is discussed, but similarities in practices are not really discussed. For example, it was found that Chimpanzees and Gorillas share similar phalangeal curvature profiles, both dealing with the pressure put on the phalanges when walking. This might be interesting to include, as it goes along with the idea that Chimpanzees and Gorillas originated from a form of fist walking similar to Orangutans (see http://scholarworks.umass.edu/open_access_dissertations/755/)

2.)	In the advantages section, not many advantages are discussed of knuckle walking over Chimpanzees’ and Gorillas’ practice of bipedalism at times. The efficiency of knuckle walking over other forms of locomotion should be discussed more, maybe in a more general sense, and then applied to certain species.

3.)	A more general section could be added that discusses the anatomical differences and implications of knuckle walking. Chimpanzees and Gorillas practice different forms of knuckle walking, which has different affects on their physiology (which is discussed in this article but could be discussed more in-depth). Does knuckle walking change their center of gravity and weight distribution? Does this have an impact on their limbs and hands? Questions like these could be addressed in this section to give readers a more comprehensive look at what knuckle walking entails.

Edits made to Wikipedia page
 Addition of the following section to the article on Knuckle-Walking (https://en.wikipedia.org/wiki/Knuckle-walking) 

Evolution of knuckle-walking
There are competing hypotheses as to how knuckle-walking evolved as a form of locomotion, stemming from comparisons between African apes. High magnitudes of integration would indicate homoplasy of knuckle-walking in gorillas and chimpanzees, in which a trait is shared or similar between two species but is not derived from a common ancestor. However, results show that they are not characterized by such high magnitudes, which does not support independent evolution of knuckle-walking. Similarities between gorillas and chimpanzees have been suggested to support a common origin for knuckle-walking, such as manual pressure distribution when practicing this form of locomotion. On the other hand, their behavioral differences have been hypothesized to suggest convergent evolution, or homoplasy.

Another hypothesis proposes that African apes came from a bipedal ancestor, as there are no differences in hemoglobin between Pan and Homo, suggesting that their divergence occurred relatively recently. Examining protein sequence changes suggests that Gorilla diverged before the clade Homo-Pan, meaning that ancestral bipedalism would require parallel evolution of knuckle-walking in separate chimpanzee and gorilla radiations. The fact that chimpanzees practice both arboreal and knuckle-walking locomotion implies that knuckle-walking evolved from an arboreal ancestor as a solution for terrestrial travel, while still maintaining competent climbing skills.

It is important to note that not all features associated with knuckle-walking are identical to the beings who practice it, as it suggests possible developmental differences. For example, brachiation and suspension are almost certainly homologous between siamangs and gibbons, yet they differ substantially in the relative growth of their locomotor skeletons. Differences in carpal growth are not necessarily a consequence of their function, as it could be related to differences in body mass, growth, etc. It is important to keep this in mind when examining similarities and differences between African apes themselves, as well as knuckle-walkers and humans, when developing hypotheses on locomotive evolution.

Due: 17 November 2014
 The Evolution of Knuckle-Walking: Moving Away from Brachiation and Implications of Further Evolution towards Bipedalism 

The evolution of knuckle-walking in large apes raises evolutionary questions regarding a need for this quadrupedal terrestrial behavior and any implications on the evolution of bipedalism in humans. Throughout the evolutionary history of primates, a great adaptability in behavioral responses to changes in environmental conditions has always been maintained (Schmidt, 2010). Evolving a new form of locomotion often is a response to environmental changes, and the new form of movement is more efficient or advantageous in some way, as is the case with natural selection. Evolution by natural selection arises due to a struggle for existence, often requiring adaptations that increase average fitness. Not only does the evolution of knuckle-walking involve the concept of natural selection, but it also applies the evolution of bipedalism in humans. The evolution of human bipedalism has many hypothesized origins, which can be better explained by examining different forms of primate locomotion (primarily knuckle-walking), and may provide further insight to our own evolution.

Knuckle-walking is a form of terrestrial quadrupedalism found in large apes, primarily African apes, and can further be explained by examining extant ape behavior and anatomy. A general trend throughout the primate radiation is that changes in body size often result in changes in locomotive behavior. While no one form of locomotion is strictly practiced by one size of primate alone, certain characteristics are associated with body size and their resulting locomotive behaviors. For example, larger primates tend to have more robust limbs that move in a straighter manner, which reduces stress on the bones and muscle load (Schmidt, 2010). However, there is a significant level of variability amongst knuckle-walking primates, both anatomically and behaviorally, that has supported several different hypotheses for its evolution.

These similarities and differences are best seen between African apes, more specifically in chimpanzees (Pan), as chimpanzees practice both arboreal locomotion and knuckle-walking. Brachiating, or swinging, primates experience passive stress on the bones when moving rather than stress due to muscle contraction, such as in digitigrade/palmigrade terrestrial primates. Due to their types of locomotion, chimpanzees’ shoulder muscles are constantly active in the swing phase of both brachiating and knuckle-walking. This results in shoulder muscles that resemble digitigrade/palmigrade primate anatomy (Kikuchi et. al., 30-38). Chimpanzees and gorillas (Gorilla) also have similar phalanges, with the greatest curvature in the fifth digit as it bears the least amount of pressure during knuckle-walking (Matarazzo, 2013). Despite similarities, variation among the knuckle-walking African apes suggests that it is not anatomically the same throughout primates. Compared to gorillas, chimpanzees show a greater variation in hand position and the digit pressed off of during knuckle-walking. Gorillas also have a lower variability in phalange length and shorter metacarpals than chimpanzees (Matarazzo, 2013). The amount of carpal variation between African apes suggests that traits of wrist morphology thought to be associated with knuckle-walking are not definitive functionally, making knuckle-walking a behavior practiced but not identical between primates (Kivell et. al, 2009). It is important to note that not all features associated with knuckle-walking are identical to the beings who practice it, as it suggests possible developmental differences. For example, brachiation and suspension are almost certainly homologous between siamangs and gibbons, yet they differ substantially in the relative growth of their locomotor skeletons. Differences in carpal growth are not necessarily a consequence of their function, as it could be related to differences in body mass, growth, etc. (Richmond et. al., 2001). It is important to keep this in mind when examining similarities and differences between African apes themselves, as well as knuckle-walkers and humans, when developing hypotheses on locomotive evolution.

There are competing hypotheses as to how knuckle-walking evolved as a form of locomotion, stemming from comparisons between African apes. High magnitudes of integration would indicate homoplasy of knuckle-walking in gorillas and chimpanzees, in which a trait is shared or similar between two species but is not derived from a common ancestor. However, results show that they are not characterized by such high magnitudes, which does not support independent evolution of knuckle-walking (Williams, 2010). Similarities between gorillas and chimpanzees have been suggested to support a common origin for knuckle-walking, such as manual pressure distribution when practicing this form of locomotion. On the other hand, their behavioral differences have been hypothesized to suggest convergent evolution, or homoplasy (Matarazzo, 2013). Another hypothesis proposes that African apes came from a bipedal ancestor, as there are no differences in hemoglobin between Pan and Homo, suggesting that their divergence occurred relatively recently. Examining protein sequence changes suggests that Gorilla diverged before the clade Homo-Pan, meaning that ancestral bipedalism would require parallel evolution of knuckle-walking in separate chimpanzee and gorilla radiations (Edelstein, 1987). The fact that chimpanzees practice both arboreal and knuckle-walking locomotion implies that knuckle-walking evolved from an arboreal ancestor as a solution for terrestrial travel, while still maintaining competent climbing skills (Richmond et. al., 2001).

A variety of hypotheses have been proposed for the evolution of bipedalism in modern humans, with origins from a variety of locomotive behaviors such as arboreal quadrupedalism, terrestrial quadrupedalism, climbing, and knuckle-walking. For example, anatomical similarities between humans and apes suggest that bipedalism evolved not from a knuckle-walking ancestor, but from a brachiating ancestor, including similarities in the trunk and development of flexion in the wrist (Pennock, 2013). Evidence seems to more strongly support the hypothesis that bipedalism in humans originated from a knuckle-walking ancestor. For this to occur, there would have to have been a fitness advantage of a more upright poster versus a more horizontal posture of terrestrial quadrupedalism (Richmond et. al., 2001). One of the most critical activities in primates is escaping from predators, as it places the most stress on the motion system (Schmidt, 2010). Having a more efficient method of escape would prove advantageous and may lead to evolution of a certain type of locomotive behavior. This concept may be used to propose why bipedalism evolved from knuckle-walking, as human bipedalism is a very efficient form of running and therefore escape. What is perplexing, however, is how large terrestrial primates, tend to be very good at fighting off predators and threats, meaning that they do not face a strong need to escape when confronted (Schmidt, 2010).

Both early and modern humans share similarities with knuckle-walking apes, supporting the knuckle-walking hypothesis. Many forelimb characteristics are shared between African apes and humans, which have been retained in humans since they are compatible with bipedalism. These features act to either stabilize the wrist and or/ to reduce the stress from vertically directed compressive loads. Both apes and modern humans exhibit similar wrist morphology, while late hominins and modern humans differ slightly. Humans possess features for greater wrist extension compared to knuckle-walkers, which is arguably related to the development and use of tools. While humans may have greater wrist extension, they share limitations with African apes in the midcarpal joint based on bone configuration. Adaptations for weight transmission have also occurred in both humans and knuckle-walkers. The fused os centrale bone in the hand provides wrist stability in an extended position, which may have been caused by compression on the bone due to body weight. Both humans and African apes have large ulnar heads in the arm and well-formed articular discs, allowing for more effective weight bearing. Early hominins and African apes have features that contribute to and suggest strong elbow extension, which is typically exhibited during knuckle-walking. An interesting behavioral similarity can be seen in juvenile movement both in African apes and humans. Palmigrade crawling is found in both, as human babies utilize this form of motion before transitioning to bipedalism, and infant apes such as chimpanzees utilize movement on palmigrade hands before transitioning to knuckle-walking (Richmond et. al., 2001).

Early hominin finger proportions and thumb length are more similar to a recent quadrupedal ancestor, yet the phalanges, both manual and pedal, exhibit a level of curvature that suggests arboreal behavior (Richmond et. al., 2001). While this might contrast a knuckle-walking hypothesis, it is important to remember that modern chimpanzees practice both arboreal and quadrupedal locomotion. Knuckle-walkers possess the ability to climb, which is why early hominins, African apes, and humans have features associated with arboreal behavior (Richmond et. al., 2001).

While it is unclear as to how knuckle-walking evolved, and the possibility of further evolution to bipedalism in humans is still disputed, evolutionary processes such as natural selection and convergent evolution can be applied to attempt to explain the relationships of different locomotive behaviors. The drive towards a more advantageous form of locomotion coincides with the concept of natural selection, but the exact relation to the evolution of knuckle-walking and bipedalism are still unclear. Research examining anatomy and behavior has exposed similarities and differences that help to formulate hypotheses but fail to provide a definitive evolutionary history. Humans are the only species of primate that has successfully and completely abandoned arboreal behavior (Schmidt, 2013). How this came to be, and how locomotive behaviors before bipedalism such as knuckle-walking evolved, are relationships that with further examination and fossil evidence could possibly provide a deeper look in to human origins.

References

Edelstein, S.J. 1987. An Alternative Paradigm for Hominoid Evolution. Human Evolution. 2: 169-174.

Kikuchi, Y., H. Takemoto and A. Kuraoka. 2012. Relationship between humeral geometry and shoulder muscle power among suspensory, knuckle-walking, and digitigrade/palmigrade quadrupedal primates. J. Anat. 220: 29-41.

Kivell, T. L. and D. Schmitt. 2009. Independent evolution of knuckle-walking in	African apes shows that humans did not evolve from a knuckle-walking	ancestor. Proc. Natl. Acad. Sci. USA. 106(34): 14241-14246.

Matarazzo, S. A. 2013. Knuckle-Walking Signal in the Manual Phalanges and Metacarpals of the Great Apes (Pan and Gorilla). Dissertations. Paper 755: vi	129.

Pennock, E. ET. 2013. From Gibbons to Gymnasts: A Look at the Biomechanics and	Neurophysiology of Brachiation in Gibbons and its Human Rediscovery. Student Works. Paper 2: 1-31.

Richmond, B. G., D. R. Begun and D. S. Strait. 2001. Origin of Human Bipedalism: The Knuckle-Walking Hypothesis Revisited. Yrbk. of Phys. Anthropol. 44: 70-105.

Schmidt, M. 2010. Locomotion and postural behavior. Adv. Sci. Res. 5:23-39

Williams, S.A. 2010. Morphological integration and the evolution of knuckle-walking. J. Hum. Evol. 58(2): 432-440