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Meet our long extinct cousin–Ardipithecus ramidus or “Ardi,” a female who happens to be the newest and oldest member of the human ancestor tree.  In the December 18 2009 issue of Science Magazine, the editors named the discovery of Ardi, whose fossilized remains date back 4.4 million years, as the scientific breakthrough of the year. This must have been a challenge for the editors of Science, as the papers first describing the investigative work on Ardi were all published in Science Magazine in 2009 in the form of 11 papers, with 47 researchers from nine different countries, collaborating to not only analyze the fossil bones of Ardi, but further characterize an additional 150,000 fossil specimens from the same dig site, located in the Afar Depression of Ethiopia. The results represent 15 years of labor-intensive investigations and extensive collaborations. While many of the insights and conclusions derived from this study have been challenged by other researchers,  no one has challenged the age, significance or authenticity of the finding. Until Ardi was discovered in 1994, our oldest hominin fossil was the famous Lucy (Australopithecus afarensis), discovered in 1974. Lucy was 3.2 million years in age, so the discovery of Ardi was a major step backward in time. And, Ardi is more transitional and primitive than Lucy.

Hominin is meant to describe all humans and human ancestors exclusive of those related to modern apes. You can learn about the various distinctions among humans and other primates here. The single requirement legitimizing membership in the hominin club is that of walking erect, as we do. Many clues point to an erect posture for Ardi, including skull changes, hand differences and pelvis structure. Ardi’s pelvis was not well preserved, so some doubt about this not so subtle feature, makes the story incomplete, or at least less certain. You can watch a video discussion among the scientists who described the original findings here. One distinctive feature of Ardi is the structure of the foot, which had an opposable toe, suggesting that she was at home swinging from tree branches grasped with her feet or hands. Thus Ardi, only slightly larger than a chimpanzee, was in transition between a pure tree dweller and a non-tree dwelling, erect-walking hominid. Ardi had a brain only slightly larger than that of  a chimpanzee, a fact that researchers take to mean our ancestors learned to walk upright before our brains acquired their large, modern size. Extensive analysis of the fossil record from the dig site suggests that Ardi hung out in an ancient floodplain, covered in woodlands, as she climbed among hackberry, fig and palm trees and lived among monkeys, kudu antelopes and peafowl. Do you see any similarity between Ardi and the features of known, living hominids of today? I think I have a direct descendant as one of my neighbors.

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Gastric-Brooding Frog

It was a PBS program that alerted me to the extinction of a frog called the gastric-brooding frog. These animals reproduce by the female swallowing the fertilized eggs and keeping them in her stomach until the young emerge as fully formed frogs. The young fertilized eggs/tadpoles secrete an unidentified substance that stops acid production in the female’s stomach and shuts down her entire digestive system, converting it from a means of sustenance into a brood pouch. After the appropriate developmental period, lasting from 36-43 days, the little frogs, about 21 to 26 of them, come out of their mother’s mouth as fully formed and ready for action (see image). The delivery process apparently takes place in the water. Two different species of these frogs were known as the Southern and Northern gastric-brooding frogs, indigenous to Queensland Australia.  Now it appears that both species are extinct. They have not been seen in the wild since the 1980s and attempts to maintain them in captivity were not successful. Like most disappearing amphibians, the cause of this extinction is unknown, but the three leading hypotheses include global climate change, fungus infections and habitat destruction, all three of which can be related to human activity, including an increasingly understood global threat to amphibians from a fungus infection.

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This month is the 150th anniversary of Charles Darwin’s On the Origin of Species, perhaps the greatest scientific and social publication in history.  Many years ago I purchased a paperback copy of Darwin’s book, a Dover publication as I recall, and read it for the first time, though not from cover to cover. At that time,  reading it more than a 125 years or so after it was first published, introduced me to the arguments, examples and logic that Darwin used to make his case: the genius of his insights and the power of his observations are not subtle in the book.  But then as now, there was little doubt or argument that evolution was the only rational way to interpret biological variance in species and the principle of natural selection seemed like a sensible way for nature to take advantage of genetic mutations, the majority of which probably give a disservice to the propagation of the species. But at the period of my reading and even more so today, evolution had become a proven fact, not a theory, a result of an expansive knowledge of biology, molecular biology and genetics, coupled with increasing clarity from the fossil record, including that of our own Hominidae and Hominina history, which, for human ancestors (Hominina), now goes back more than 4 million years. We know more about evolution than we do about the structure of the atom and each new piece we find in the puzzle, such as the ever-expanding Hominina fossil record, gives us an increasingly broad insight of our ancestors’ culture and behavior, all achieved through slow changes that reveal a story about a species that started to walk erect before it developed its large brain. But at the time that Darwin published his book, there was virtually no knowledge of genetics and only a very primitive grasp of the fossil record that supported such a sweeping interpretation of species origins and connectivity. Darwin did however acquire fossils during his trip to the Galapagos Islands beginning in 1831.  He  made his case for evolution based on the animals that he retrieved for study, including many birds, and the evolutionary-like changes that man had created through domestication of certain species, particularly dogs. Though Darwin had no knowledge that the code for reproduction was within our DNA, which would not be identified until well into the next century, and he did not have knowledge of Gregor Mendel’s work on plant genetics and the nature of inheritability, his  introduction of natural selection as the key to adapting mutational change for  improved chances of species survival, was the most insightful feature of his argument. Darwin’s genius was in recognizing that a vast change in species could be achieved over time, through minute, advantageous and heritable traits that would initially appear to be small. As one example, he used the evolution of the eye from invertebrates to mammals as an illustration of the differences in optical qualities that could be achieved through natural selection, advantageous changes and a whole lot of time. The time required for these changes remains incomprehensible for humans to absorb.

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