From: Zardoz ® 19/11/2001 8:04:55 Subject: re: MEDICAL FAQ NOTES post id: 501856 Savannah Theory Ever since Darwin's Origin of Species, there has been a raging debate concerning the exact lineage of man. Today, one hundred and forty years after Darwin's bombshell, the debates revolve around the timing of the split between man and ape and the location of the environment where the evolutionary leap most likely took place. There are two widely accepted evolutionary models, the Savannah Theory and the Mosaic Theory, and one extremely controversial model, the Aquatic Ape theory. I will discuss the Savannah Theory first since it is the most widely accepted, the Aquatic Ape Theory second as it is in direct opposition to the Savannah Theory, and the Mosaic Theory last because it is a melding of the two. To begin I will give a brief explanation of the Savannah Theory. Basically, the theory states that between 5 and 8 million years ago, at the end of the Miocene epoch, a drying period enveloped equatorial Africa. As a result of this drying, the Miocene forest began to shrink, forcing the apes to begin to make the transition to a terrestrial way of life. Many of the genera of apes at the time likely became extinct during the transition, and those that made the transition to terrestrial life survived. The early apes that began to live on the emerging African savannah likely retained their aboreal abilities, being active on the savannah during the day to return to the trees at night. From at least one of these early terrestrial apes would evolve humankind as it is today. The original theory, in the strictest sense, confined itself to the open grassland-savannah as an available niche for the transition to the bipedal hominids. Early theorists suggested that bipediality evolved as the earlier hominoids made the transition from a tree dwelling omnivore to that of a ground dwelling omnivore on the savannah. Some suggested that life on the savannah increased the danger of becoming the meal of a predator; therefore, early hominoids began to stand erect in order to scan the horizon for prey. Others theorize that this same as hominoids began to scan for prey. Today, however, most scientist conclude that this transition took place in a woodland-savannah where the developing hominids could move about on the grassland and still escape to the forest when threatened by predators. In his article The Antiquity of Human Walking, John Napier says this of the transition to bipediality and its correlation to the woodland-savannah evolutionary niche "It has enough trees to provide forest foods and ready escape from predators. At the same time its open grassy spaces are arenas in which new locomotor adaptations can be practiced and new foods can be sampled. In short, the woodland-savanna provides an ideal nursery for evolving hominids." Professor Nancy Makepeace Tanner also puts forth another highly probable scenario. Tanner proposes gathering- a new way of exploiting plant food with tools- as a basis for hominid divergence. In her book, On Becoming Human, Tanner discusses the topic "Gathering and Bipedalism" in which she states: Walking long distances while carrying is essential to this food pattern. A long-range gathering and foraging strategy was what was developing during the transition to Australopithecus. Mobility over large expanses for both females and males, and effective carrying, was made feasible by the development of a system of upright, two-legged locomotion. There was much to be carried by the gathering mothers-their infants, their tools, and the gathered food. Selection operated on the bipedal behavior present in the ancestral population; as the transitional population began to exploit the new niche, the new locomotor pattern rapidly became an integral part of it. Bipedalism freed the arms and hands from locomotor functions and body support. The change from four limbs of support to but two created problems of balance and stability that were met by anatomical modifications of the pelvis, limbs, and feet. The muscles and joints of the pelvis and lower limb changed; the legs became longer and massive and the ankle and foot developed for support rather than mobility; the first toe lost its ability to oppose other toes as the foot developed for support. The upper limbs and trunk were reduced in mass and length. Concurrently, the motor skills of the hands were developing for manipulation of objects in many contexts, especially in relation to collecting food. This is a very likely scenario because it provides impetus for both the transition to the savannah and an immediate reward (food) for covering the ever-expanding areas of their changing environment. http://members.fortunecity.com/lucyjune1/anthropologpy/ evolution_of_the_hominids_resear.htm Evolution of the Hominids