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In Search of Our Ancestors

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In Search of Our Ancestors

Bài gửi by Hasuongkch on Tue Mar 23, 2010 11:40 am

Bạn nào dich bài này ko? Post bài dịch lên mọi người tham khảo với nhé!
Mình post tiếng Anh lên trước ha.
In Search of Our Ancestors
Following in the footsteps of his parents, famous British paleoanthropologists Louis and Mary Leakey, Kenyan paleoanthropologist and conservationist Richard Leakey has discovered many important fossils of early humans and the ancient relatives of humans. In this essay, Leakey recounts two important finds: his discovery of a 1.6-million-year-old skeleton of a young male Homo erectus, and his wife’s unearthing of a jawbone of an ancient hominid. Leakey also explains the painstaking process of searching for fossils, from selecting an initial site to excavating fossils one fragment at a time.


In Search of Our Ancestors
By Richard Leakey

A large part of the extraordinary excitement and satisfaction of finding a major new fossil comes from the anticipation of discovery. To a great extent a qualified field prospector is in possession of certain ideas and images of what is being looked for and so during the search, which can go on for days or even longer, there is always the stimulus of one’s imagination. I compare this with the excitement and stimulation that I get when reading an imaginative menu or a good gourmet recipe. Of course, as we all know, the meal can sometimes be disappointing and so it is with fossils. I, however, am easily persuaded that there is always something better and I don't stop reading menus or buying the latest books on gourmet cooking!

Human paleontologists are looking for hard data that will provide enduring evidence for the evolution of our own species. Over the past one hundred years, countless expeditions have been organized in many parts of the world to search for fossils and there have been remarkable successes. What few people realize outside the profession is that a far larger proportion of these endeavors fail to come up with anything useful. Patience and real dedication is a prerequisite for field workers whether they are working in Africa or the localities of Asia, the Far East, or China. Remains of human ancestors are rare, often fragmentary, and generally the sites are today remote and difficult to work.

The body of evidence supporting human evolution is remarkably complete and it cannot be long now before scientists will have gained an enduring and widely accepted analysis of the main events in our species' past. New data will continue to become available and the field work will continue for many more years. There will always be the need for more complete specimens or even new additional fragmentary fossils which increase the sample and so broaden and deepen confidence in the analysis of previous discoveries.

My own experiences started with the early exposure that I had as a child when my brothers and I would be taken off to fossil sites that my parents Louis and Mary were investigating. I will never forget the excitement and pure joy when they had a major find and in later years, working with my wife Meave and other colleagues, we have been privileged to have similar unique moments.

Fossil remains of early human and prehuman species have been discovered in Africa regularly since the first find was made and announced in South Africa in 1924. Before that, fossils of what seemed to be ancestral humans had been found in China and Indonesia. The first African find of the so-called “Ape Man” had been anticipated since Charles Darwin had predicted that human ancestors would be found in Africa. Since 1924 every fossil hominid has contributed to the complex picture of how, where, and when humans evolved. Each new discovery adds to the clarity of the total picture although some finds simply confirm or consolidate earlier work. Others dramatically change the detail if not the composition of the picture itself. When searching for fossils, most field workers have a preconceived idea of what we need to find to get acceptance of “our” theories and so we are “looking” for a specimen that will “confirm or prove” the validity of these ideas. Of course, proving that a colleague has got it all wrong can be an equally powerful motive.

The first step in the process of finding fossils is to select a location where there is at least the potential for finding what you are looking for. The most basic starting point is geology: there has to have been the right geological conditions for organic remains of life to have become fossilized and so preserved in the first place. A combination of these “right conditions” is quite rare.

Many of the locations that I have worked are where ancient rivers once flowed into lakes. On the shallow deltas of these ancient rivers, bones of animals that died or were killed by predators, not only accumulated as they swept down from upstream by torrential rains, but they were also buried under flood plain silts and sand carried by the flood waters. Once bones are buried, especially if the soils are not acidic, the process of fossilization (or mineralization) will begin and in time, a bone becomes a fossil.

There are many other ways in which fossils are formed and cave deposits come to mind because of the very extensive fossil human ancestor collections that have been made in South America.

Deposits containing fossils have to be excavated to recover fossils and one has absolutely no idea where to begin. In caves, fossils are often first found when people have been excavating for limestone or other commercially useful minerals. In the instance of the ancient lakes and deltas, fossils are initially excavated by nature and are found on the surface. Erosion processes are exposing the layers in which fossils are preserved and from surface discovery, it is possible to predict where, through further excavation, other fossils will perhaps be found. Frustratingly, natural erosion often leaves little behind and there have been a great many hours spent in meticulous excavation with no returns of any importance.

The best way to illustrate the circumstances of a major discovery is to describe two entirely different events, one where our excavations were fabulously rewarding and once where a find, exposed by natural erosion, dramatically confirmed my own expectations of what was happening to our early ancestors some 4 million years ago.

In 1984, an expedition that I had organized was systematically exploring the exposed, heavily eroded sedimentary strata which lie along the western margin of Kenya's Lake Turkana. We knew that there were fossils to be found but most of the material was very broken, because of trampling by the hooves of goats and sheep that wander incessantly over these barren lands. Our prospects of finding any well preserved or reasonably complete specimens seemed pretty remote and it was for this reason that a find of a small piece of human skull lying among the lava cobbles near the camp initially evoked little enthusiasm. The fragment itself was nondescript and Kamoya Kimeu, who discovered it, was not hopeful that much more would be found. He had failed to see any other pieces during a surface search of over an hour. We decided to screen the area anyway, passing the loose top soil from the slope in the immediate vicinity of the fragment, through a fine mesh wire sieve. This process is tedious and dusty and you can imagine the surprise and delight when several other small pieces of the skull turned up at the end of the first day's effort. With growing hope, the work on the second day began at dawn and again a number of pieces were found. It was becoming clear that a good part of a skull had only recently been exposed and broken up and we had a good chance of getting enough of the pieces to reconstruct a useful specimen.

By the end of the fourth day we had not only found most of the skull but some fragments of ribs and a piece of the scapula had been recovered from the sieving. At this point the surface sieving was completed and an exploratory excavation was started to see if any of it and the specimen was still buried in the strata. Within days, we found the first parts of the skeleton, in situ, undisturbed since their being covered by silts and sands some 1.7 million years before.

Over the next few weeks, we would awake well before dawn so that we could be at work at first light. Each day, several new finds were uncovered and each was something that was new to science: we were exposing parts of the skeleton of a young male Homo erectus and most of the skeletal elements had previously never been found anywhere in the world. An incredible experience it was!

In excavation of the kind we were doing, a very sharp but delicate probe like an ice pick is pushed into the earth for a depth of about an inch. This breaks the earth away and by repeated probes, one removes a layer of sediment about a cubic inch at a time. The procedure requires the excavators to work in levels and never to dig deeply or hurriedly. As one probes into the ground you can feel any change in the substance of the earth: a fossil bone is hard and you “sense” its presence through the tip of the probe. The critical skill is to press without too much force so that no fossil is damaged. Once you have detected that there is something, a delicate dental pick and fine brush are used to investigate the hidden “hardness.” If it is a fossil, the excavator then carefully clears away the earth, often a few grains at a time.

In this way, an almost entire skeleton was uncovered over a period of weeks and I believe those days were among the most exhilarating and rewarding that I have ever lived through. Each day, something quite new and all the bones were so incredibly well preserved and complete.

Sadly, some parts we never found; presumably they became separated from the main skeleton at the time of burial but in an attempt to find these missing parts, we excavated at the site for 2 months, each year, for 4 years.

The last two seasons were as frustrating and empty as the first had been rewarding. Each day, one probed but no hardness was felt and eventually, after excavating some 1500 cubic meters, we closed the excavations and called it a day. What a “day” it had been though, and I doubt if there are many people alive who have enjoyed such a prolonged natural high in the deserts of northern Kenya.

More recently, in 1995, I was visiting my wife Meave who was leading her expedition that was searching for fossils at a site off the southwestern shores of Lake Turkana. She had been quite successful and over several seasons, a number of surface finds had been made but, frustratingly, all of these were fragments. Nothing had been found which could enable a clear and unambiguous determination as to whether or not the fossils represented a hitherto undiscovered stage in human evolution.

The deposits that were being explored were approximately 4 million years old and there was every chance that at this age, the species would show more primitive features and in this regard perhaps be more like the chimpanzee. Fossils from other sites such as the Hadar in Ethiopia, Laetoli in Tanzania and a few other Kenya localities had provided good clues and pointers and at least from my perspective, I could imagine what a skull or complete jaw would look like. This, if you like, was the “menu” stage—enjoying the excitement of thinking about what might be found. My hope was that a discovery would be made while I was in the field so that I could participate in the “moment of truth” when a new find is first seen by informed eyes.

The moment came late one morning. I was sitting in a small hole on the slope of a hill where I had been helping to excavate an elephant skull. We were about to return to camp for lunch when I noticed one of my wife's colleagues running as fast as he could towards our hill. My thoughts were either there has been an accident such as a snake bite, or attack by bandits, or else something very special had been found. Nobody runs across the rock-strewn desert at noon in temperatures of over 119° without very good reason.

Meave went off to meet the fast-approaching man and after a hurried exchange of words, they both ran off at high speed. I knew that it had to be a discovery because, otherwise, the information would have been shared. I could not immediately follow them because I walk on artificial limbs and these I had taken off during the excavation of the elephant. Anyway, in a few minutes, I too was on my way and when I eventually caught up with Meave, her shining eyes said it all—a significant find had indeed been made. Peter Nzube had found a complete lower jaw of the early hominid and it was sufficiently complete for us to know at once that it was a new and quite primitive species.

The details of the teeth and the almost parallel positioning of the tooth rows left me in no doubt at all. It was really exciting and although we had hoped for something new and different, the actual find was a surprise. Going back to the analogy of the menu and the good meal, the meal was in fact better than I had dared hope for.

The work at Lake Turkana continues and I am always hopeful that Meave and her team will find more surprises. I know that it is the anticipation of such surprises that keeps them going, too, in the extreme conditions that they have to work under.

About the Author: Richard Leakey is a paleoanthropologist and co-author, with Roger Lewin, of Origins and other books.
"In Search of Our Ancestors."Microsoft® Encarta® Encyclopedia 2001. © 1993-2000 Microsoft Corporation. All rights reserved.

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Re: In Search of Our Ancestors

Bài gửi by anhthu8x_ct on Sun Jun 06, 2010 9:47 pm





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Re: In Search of Our Ancestors

Bài gửi by anhthu8x_ct on Sun Jun 06, 2010 9:53 pm






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Re: In Search of Our Ancestors

Bài gửi by anhthu8x_ct on Sun Jun 06, 2010 9:54 pm






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Re: In Search of Our Ancestors

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