11. Human Evolution

Climate and Human Evolution

2014-12-04. Dwindling African tribe may have been most populous group on planet. By Ann Gibbons, Science.

2010 March 1. Human Culture, an Evolutionary Force. By Nicolas Wade, NY Times. Excerpt: As with any other species, human populations are shaped by the usual forces of natural selection, like famine, disease or climate. A new force is now coming into focus. It is one with a surprising implication — that for the last 20,000 years or so, people have inadvertently been shaping their own evolution.
...Although it does shield people from other forces, culture itself seems to be a powerful force of natural selection. People adapt genetically to sustained cultural changes, like new diets. And this interaction works more quickly than other selective forces, “leading some practitioners to argue that gene-culture co-evolution could be the dominant mode of human evolution,” Kevin N. Laland and colleagues wrote in the February issue of Nature Reviews Genetics. Dr. Laland is an evolutionary biologist at the University of St. Andrews in Scotland....

2009 October 4. Ardipithecus: We Meet At Last. By Carl Zimmer, Discover. Excerpt: Meet Ardipithecus.
This introduction has been a long time coming. Some 4.4 million years ago, a hominid now known as Ardipithecus ramidus lived in what were then forests in Ethiopia. Fifteen years ago, Tim White of Berkeley and a team of Ethiopian and American scientists published the first account of Ardipithecus, which they had just discovered. But it was just a preliminary report, and White promised more details later, once he and his colleagues had carefully prepared and analyzed all the fossils they had unearthed. “Later,” it turned out, meant 15 years.
...Today, the journal Science has handed many of its pages over to White and his colleagues, who have filled them with lots of details about Ardipithecus.... Ardipithecus has gone from being an enigmatic collection of bones to a new touchstone for our early hominid ancestors....
C. Owen Lovejoy of Kent State University spearheaded the studies on how Ardipithecus moved. He and his colleagues argue that its pelvis could support its upper body during bipedal walking. It wasn’t a fabulous walker, and was probably a terrible runner. Nevertheless, it had some of the same anchors for muscles that we have on our pelvis, and which chimpanzees and other apes lack....
...Ardipithecus’s feet...were adapted for walking on the ground. Yet the big toe was still opposable, much like our thumbs. This sort of big toe helped Ardipithecus move through the trees much more adeptly.... Ardipithecus probably moved carefully through the trees, using its hands and feet all at once to grip branches....

2008 November 27. Did Neanderthal cells cook as the climate warmed? By Ewen Callaway, New Scientist. Excerpt: Neanderthals may have gone extinct because their cells couldn't cope with climate change, according to a new hypothesis...
Metabolic adaptations to Ice Age Europe may have proved costly to Neanderthals after the continent's climate started to change, says Patrick Chinnery, a molecular biologist at Newcastle University, UK.
He and colleague Gavin Hudson identified potentially harmful mutations in the newly sequenced Neanderthal mitochondrial genome. In particular, the researchers found genes that are associated with neurodegenerative diseases and deafness. "If they were found in modern humans they would be bad news," Chinnery says.
The extinction of Neanderthals, close relatives of modern humans, some 25,000 years ago remains unexplained.
...Chinnery and Hudson suggest that mutations in mitochondria helped Neanderthals cope with the cold weather, but that when the climate started fluctuating between warm and cold periods, they were at a disadvantage.
In all cells, from yeast to human, a mitochondrion's main job is to produce the energy that powers cells... Our mitochondria do this quite efficiently under ideal conditions...
Mutations that sap this efficiency would generate heat instead - a potentially useful trick for Neanderthals who are known to have had adaptations to cold weather, Chinnery says. However, a warmer and less climatically stable habitat could have spelled trouble for Neanderthals with such mutations....

2008 August 14. Graves Found From Sahara’s Green Period. By JOHN NOBLE WILFORD, The New York Times. Excerpt: When Paul C. Sereno went hunting for dinosaur bones in the Sahara, his career took a sharp turn from paleontology to archaeology. The expedition found what has proved to be the largest known graveyard of Stone Age people who lived there when the desert was green.
The first traces of pottery, stone tools and human skeletons were discovered eight years ago at a site in the southern Sahara, in Niger. After preliminary research, Dr. Sereno, a University of Chicago scientist who had previously uncovered remains of the dinosaur Nigersaurus there, organized an international team of archaeologists to investigate what had been a lakeside hunting and fishing settlement for the better part of 5,000 years, originating some 10,000 years ago.
...the team described finding about 200 graves belonging to two successive populations. Some burials were accompanied by pottery and ivory ornaments....
...The sun-baked dunes at the site, known as Gobero, preserve the earliest and largest Stone Age cemetery in the Sahara, Dr. Sereno’s group reported...
Other scientists said the discovery appeared to provide spectacular evidence that nothing, not even the arid expanse of the Sahara, was changeless. About 100 million years ago, this land was forested and occupied by dinosaurs and enormous crocodiles. Around 50,000 years ago, people moved in and left stone tools and mounds of shells, fish bones and other refuse. The lakes dried up in the last Ice Age.
Then the rains and lakes of a fecund Sahara returned about 12,000 years ago, and remained, except for one 1,000-year interval, until about 4,500 years ago. Geologists have long known that the region’s basins retained mineral residue of former lakes, and other explorers have found scatterings of human artifacts from that time, as Dr. Sereno did at Gobero in 2000.
“Everywhere you turned, there were bones belonging to animals that don’t live in the desert,” he said. “I realized we were in the green Sahara.”...

2008 May 9. How the Sahara Became Dry & Climate-Driven Ecosystem Succession in the Sahara: The Past 6000 Years. Jonathan A. Holmes. Science 9 May 2008: Vol. 320. no. 5877, pp. 752 - 753 DOI: 10.1126/science.1158105. Excerpt: Around 14,800 years ago, a strengthening of the summer monsoons led to a dramatic increase in North African lakes and wetlands and an extension of grassland and shrubland into areas that are now desert, creating a "green Sahara" (see the first figure). ...a lake sediment record ... sheds light on how this "African Humid Period" came to an end.

2008 May 9. Climate-Driven Ecosystem Succession in the Sahara: The Past 6000 Years. S. Kropelin, et al. Science: Vol. 320. no. 5877, pp. 765 - 768 DOI: 10.1126/science.1154913. Excerpt: Desiccation of the Sahara since the middle Holocene has eradicated all but a few natural archives recording its transition from a "green Sahara" to the present hyperarid desert. Our continuous 6000-year paleoenvironmental reconstruction from northern Chad shows progressive drying of the regional terrestrial ecosystem in response to weakening insolation forcing of the African monsoon and abrupt hydrological change in the local aquatic ecosystem controlled by site-specific thresholds. Strong reductions in tropical trees and then Sahelian grassland cover allowed large-scale dust mobilization from 4300 calendar years before the present (cal yr B.P.). Today's desert ecosystem and regional wind regime were established around 2700 cal yr B.P. This gradual rather than abrupt termination of the African Humid Period in the eastern Sahara suggests a relatively weak biogeophysical feedback on climate. ...One of the most prominent environmental changes of the past 10,000 years is the transition of northern Africa from a "green Sahara" during the early Holocene "African Humid Period" to the world'slargest warm desert today. Detailed knowledge of the tempo and mode of this transition is crucial for understanding the interaction between tropical and mid-latitude weather systems and the multiple impacts of mineral aerosols exported from the Sahara on global climate and distant ecosystems....


2007 November 13. Jawbone Sheds Light on Divergence of Humans and Apes. By HENRY FOUNTAIN, NY Times. Excerpt: Scientists who study the divergence of humans from the other great apes have been stymied by a lack of evidence. It is thought that humans and chimpanzees split 6 million to 7 million years ago, and humans and gorillas a couple of million years before that. But almost no ape fossils from this period - the Late Miocene - have been found in Africa.
So some scientists suggest that an interloper of sorts, an ancient ape from Eurasia, returned 10 or 11 million years ago to Africa and became the last common ancestor of humans and the African great apes.
The discovery of a 10-million-year-old jawbone with teeth, in deposits of volcanic mud in Nakali, Kenya, may help put such thoughts to rest.
Yutaka Kunimatsu of Kyoto University in Japan and colleagues report in The Proceedings of the National Academy of Sciences that the fossil, the first of such vintage to be found in the region since 1982, represents a new genus of great ape....

2007 October 2. Fossil DNA Expands Neanderthal Range. By NICHOLAS WADE. NY Times. Excerpt:
In the Treaty of Tordesillas, Spain and Portugal divided the world outside Europe between them. That was not the first time that two rival groups carved up the globe. More than 50,000 years ago, all the world outside Africa was divided between two archaic human species.
The Neanderthals held sway in Europe and the Near East, bottling up the troublesome ancestors of modern humans in Africa, and Homo erectus dominated East Asia. But a new discovery suggests that this division of the world may not have been quite so clear-cut.
...Svante Paabo at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany... has shown that Neanderthal DNA can be picked out and identified. So far, he and others have identified DNA from 13 European Neanderthals.
He and colleagues have now identified Neanderthal mitochondrial DNA in bones at two new sites, they say in an article published electronically in Nature this week. One is Teshik Tash, in Uzbekistan, some 750 miles east of the Caspian Sea and, until now, the easternmost known limit of Neanderthal territory. The other bones are from the Okladnikov cave in the Altai mountains, some 1,250 miles farther east.
This huge extension of the Neanderthal's known range puts them well into southern Siberia.
Because the mitochondrial DNA sequence of the new finds differs only slightly from that of the European Neanderthals, Dr. Paabo believes that they may have moved into Siberia relatively late in the Neanderthal period, perhaps as recently as 127,000 years ago, when a warm period made Siberia more accessible.
If Neanderthals penetrated as far as Siberia, might they have reached ever farther east, trespassing far into the assumed domain of Homo erectus? "We now know that they are on the doorstep to Mongolia and even China, so I would not be surprised if we one day find a Marco Polo Neanderthal," ....

2007 June 26. Humans Have Spread Globally, and Evolved Locally. The New York Times. By NICHOLAS WADE. Excerpt: Historians often assume that they need pay no attention to human evolution because the process ground to a halt in the distant past. That assumption is looking less and less secure in light of new findings based on decoding human DNA. People have continued to evolve since leaving the ancestral homeland in northeastern Africa some 50,000 years ago, both through the random process known as genetic drift and through natural selection. A striking feature of many of these changes is that they are local. The genes under selective pressure found in one continent-based population or race are mostly different from those that occur in the others. These genes so far make up a small fraction of all human genes. The new scans for selection show so far that the populations on each continent have evolved independently in some ways as they responded to local climates, diseases and, perhaps, behavioral situations. The concept of race as having a biological basis is controversial, and most geneticists are reluctant to describe it that way. But some say the genetic clustering into continent-based groups does correspond roughly to the popular conception of racial groups.

2006 September 21. Little Girl, 3 Million Years Old, Offers New Hints on Evolution. By JOHN NOBLE WILFORD. NY Times. Excerpt: If the fossil Lucy, the most famous woman from out of the deep human past, had a child, it might have looked a lot like the bundle of skull and bones uncovered by scientists digging in the badlands of Ethiopia. The paleontologists who are announcing the discovery in the journal Nature today said the 3.3-million-year-old fossils were of the earliest well-preserved child ever found in the human lineage. It was ... a member of the Australopithecus afarensis species, the same as Lucy's.
An analysis of the skeleton revealed evidence of a species in transition, ...afarensis walked upright, like modern humans. But gorillalike arms and shoulders suggested that it possibly retained an ancestral ability to climb and swing through the trees. ...The Dikika girl's brain size ...was about the same as that of a similarly aged chimpanzee, but a comparison with adult afarensis skulls indicates a relatively slow brain growth slightly closer to that of humans. ...hyoid bone ...a rarely preserved bone in the larynx, or voice box, that supports muscles of the throat and tongue. ... appeared to be primitive and more similar to those found in apes than in humans, the scientists said, but is the first hyoid found in such an early human-related species and thus important in research about the origins of human speech.
The first relatively complete shoulder blades to be found in an australopithecine individual was one of the most puzzling aspects of the discovery, several scientists said. The lower body appeared to be adapted for upright walking by afarensis. But the shoulders and long arms were more apelike.

15 November 2005. A Conversation with Carel Van Schaik: Revealing Behavior in 'Orangutan Heaven and Human Hell'. By CONNIE ROGERS, NY Times. Excerpt: People keep asking Carel van Schaik if there is anything left to discover in fieldwork. "I tell them, 'A lot,' " said Dr. van Schaik, the Dutch primatologist. "Look at gorillas. We've been studying them for decades, and we just now have discovered that they use tools. The same is true for orangutans." In 1992, when Dr. van Schaik began his research in Suaq, a swamp forest in northern Sumatra, orangutans were believed to be the only great ape that lived a largely solitary life foraging for hard-to-find fruit thinly distributed over a large area. Researchers thought they were slow-moving creatures - some even called them boring - that didn't have time to do much but eat. But the orangutans Dr. van Schaik found in Suaq turned all that on its head. More than 100 were gathered together doing things the researchers had never seen in the wild.

January 2005. Popular Science, Evolution's Small Wonder. By TABITHA M. POWLEDGE. Excerpt: A three-foot-tall "hobbit" who lived in Indonesia up to 12,000 years ago is changing the way we think about the human family. She was only three feet tall? And her brain was smaller than your average chimp's. Yet she and her relatives apparently lived fully human lives. They seem to have made sophisticated tools, cooperated to find food and cook it, and perhaps even buried their dead with ceremony. The startling discovery of bones from hobbit-size humans who lived on the Indonesian island of Flores as recently as 12,000 years ago-a time when our own species had already populated the Americas-has scientists revising their ideas about the skills of other humans in our growing family tree and about the importance of brain size. Peter Brown of the University of New England in Australia, who leads the team that's examining the bones, says it was a major surprise to find tools, including points and hafted microblades, associated with Homofloresiensis, as the new human family member has been named. The tools are like those previously seen only with European fossils from our own species, Homo sapiens, Brovn notes, and the oldest of them were made 94,000 years ago. Homo sapiens is thought to have arrived in the region a mere 40,000 years ago, much too late to be responsible for the implements. If this tiny human made the tools, then the internal structure of its brain must have been more like our own than a chimps despite being just a third the size of ours. Of the six species of humans known, all extinct except ours, this is by far the smallest-brained human scientists have ever seen. The researchers suspect that H. floresiensis is a dwarfed descendant of H. erectus, to which it is anatomically similar. This is not so strange as it might at first sound. When organisms are isolated in regions with scarce resources but few predators, being big is a disadvantage and evolution tends to shrink them, a process known as island dwarfing. There are other examples on Flores, notably an extinct dwarf elephant, Stegodon....

15 February 2005. For Neanderthals and Homo Sapiens, Was It De-Lovely? By JOHN NOBLE WILFORD, NY Times. The scientists did not get around to the nitty-gritty question until the fourth hour of a two-and-a-half-day symposium on Neanderthals, held recently at New York University. A strong consensus was emerging, they agreed, that the now-extinct Neanderthals were a distinct evolutionary entity from modern humans, presumably a different species. They were archaic members of the human family, robust with heavy brow ridges and forward-projecting faces, who lived in Europe and western Asia from at least 250,000 years ago until they vanished from the fossil record about 28,000 years ago. Neanderthals may have seen their first modern Homo sapiens some 100,000 years ago in what is now Israel. The two people almost certainly came in contact in Europe in the last centuries before the dwindling Neanderthal population was replaced forever by the intruding modern humans. >

February 2005. Boning Up On Human Evolution By David Pescovitz, Science Matters @ Berkeley. Tim White, a UC Berkeley professor of Integrative Biology, is on what he calls "a planetary mission," but the planet he's exploring is Earth, albeit a very long time ago. White and an international team of scientists are digging deep into the geological record of remote Ethiopia to find clues about this planet as it existed 6 million years ago. What was the weather like? What kinds of plants thrived? What animals roamed the terrain? And, of particular interest to paleoanthropologists like White, what did our ancestors look like before evolution transformed them into us?

26 August 2004. Scientists warn of new Anthropocene age -- Should we recognize new epoch of human influence? By Clive Cookson, Financial Times. STOCKHOLM, Sweden - Scientists are beginning to accept that Earth has entered a new geological epoch, the "Anthropocene", so named because humans have come to rival nature in their impact on the global environment. The EuroScience forum in Stockholm heard on Thursday that climate change was the most obvious of a complex range of man-made effects that is rapidly changing the physics, chemistry and biology of the planet. Paul Crutzen, the Nobel Prize-winning atmospheric chemist who first proposed the term Anthropocene four years ago, said the concept was winning wide acceptance from colleagues in other fields.

April 2004. Human Evolution: Interpreting Evidence. An approach to teaching human evolution in the classroom--article by Jerry DeSilva, Boston Museum of Science. Perhaps the best topic teachers can use to exemplify the nature of science is paleoanthropology, the study of human evolution through the fossil record. Science educators have an opportunity to tackle 'How do we know?' questions by examining evidences of our past and accurately defining the terms "hypothesis," "fact," "theory" and "belief." They can use recent discoveries to demonstrate that science is a self-correcting mechanism of understanding the world. By examining different hypotheses, they can encourage the skepticism, debate and challenge to authority on which science thrives. ...In this paper, we present an updated approach to teaching human evolution, and a model for explaining what science is and how it is done.

4 March 2004. New Ethiopian fossils are from 6-million-year-old hominid living just after split from chimpanzees. By Robert Sanders. BERKELEY - Paleoanthropologists from the University of California, Berkeley, and the Cleveland Museum of Natural History have found more fossils of a nearly 6-million-year-old human ancestor first reported three years ago, cementing its importance as the earliest hominid to appear after the human line diverged from the line leading to modern chimpanzees.

11 June 2003. 160,000-year-old fossilized skulls uncovered in Ethiopia are oldest anatomically modern humans. Robert Sanders, UC Berkeley News. BERKELEY - The fossilized skulls of two adults and one child discovered in the Afar region of eastern Ethiopia have been dated at 160,000 years, making them the oldest known fossils of modern humans, or Homo sapiens.

11 July 2001. UC Berkeley/ Paleoanthropologists find oldest human ancestor in Ethiopia. By Robert Sanders, Media Relations, Berkeley. Scouring the dry washes encircling an Ethiopian site where scientists seven years ago found fossils of 4.4 million-year-old human ancestors, University of California, Berkeley, graduate student Yohannes Haile-Selassie has found even older fossils that show human ancestors walked on two legs as early as 5.2 million years ago. The fossils are the earliest hominid known, and date from close to the time when human ancestors are believed to have split off from the chimpanzees on the first steps of their evolutionary trip to modern Homo sapiens. The fragmentary fossils, which include teeth, a jawbone, hand, arm and collar bones, and one toe bone, appear to be from family members of the species discovered in 1994 by an international team led by UC Berkeley paleoanthropologist Tim White. They named that species Ardipithicus ramidus, and concluded that it was the earliest known human ancestor. Haile-Selassie, for now, has designated the new fossils as a subspecies of this earlier find: Ardipithicus ramidus kadabba.

RIFT VALLEY FEVER. Scientists are learning that the key to predicting certain epidemics --like Rift Valley fever in Africa or Hanta virus in the U.S. -- lies in an unexpected place: the ocean. Researchers at NASA Goddard Space Flight Center and at the Walter Reed Army Institute of Research have discovered that outbreaks of Rift Valley fever follow sudden floods triggered by El Niño and a similar (yet lesser-known) climate disturbance called the "Indian Ocean Dipole." Using weather satellites to track sea surface temperature patterns in the Indian and Pacific oceans, they now believe they have found a way to predict outbreaks up to five months in advance.

 

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