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The fossilized pelvis of a Homo erectus woman who lived 1.2 million years ago on the banks of an Ethiopian river has been discovered, and while researchers say it casts new light on human evolution, some of their conclusions are challenging previous theories about these early human ancestors. The pelvis reveals a short, squat woman who wasn’t built for long-distance running, but also a woman with a wide birth canal to accommodate big-brained infants.

Study coauthor Scott Simpson says the pelvis’s wide birth canal indicates that hominds’ increasing brain size was a driving factor in human evolution. Getting through the birth canal is “the most gymnastic thing we ever do,” he says. To accommodate big-brained babies, humans must have developed larger and wider birth canals over time, but with few pelvic fossils, researchers had little idea when these changes began. The Busidima pelvis shows that a wide birth canal was already in place 1.2 million years ago [New Scientist].

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Two separate groups of researchers have developed a non-invasive test for Down syndrome, using only a blood sample from the pregnant woman to examine the fetus’ DNA. While the genetic tests are still in clinical trials, experts are hailing the achievement as significant because current prenatal tests like amniocentesis require inserting a needle in the uterus, and carry a risk of miscarriage.

A biotechnology company called Sequenom says it will begin selling its test next June, while researchers from Stanford, who just published their results in the Proceedings of the National Academy of Sciences, are still planning a large-scale clinical trial. Some experts say that the results are somewhat preliminary, and should be viewed cautiously: The Stanford test has been tried on only 18 blood samples. Sequenom has tried its test on only about 400 samples and has not yet published its results in peer-reviewed journals. Still, both tests have perfect records so far: no false negatives or false positives. “This is quite simply a major step forward, if it works at all like we expect it might,” [says Down Syndrome expert] Jacob A. Canick [The New York Times].

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A new analysis of the skulls of three Neanderthal babies shows that the cranium of a newborn Neanderthal was about the same size as that of a newborn Homo sapiens, and that the Neanderthal children grew faster than modern humans in the first few years of life. The report on the young skeletons, which date from between 45,000 to 50,000 years ago, adds fuel to the debate over how similar Neanderthal culture was to that of our early Homo sapiens ancestors.

A big-headed infant skeleton found in Russia suggests that childbirth was no easy task for for Neanderthal women. Neanderthal mothers had slightly larger birth canals, but the prominent face of Neanderthal babies made it just as hard to push out as a modern human. This suggests that both groups had the social structures needed to help with childbirth [New Scientist].

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Older men have an increased risk of fathering children who eventually develop bipolar disorder, according to new research. It’s the latest study to refute the earlier theory that men could father children into their old age with no ill effects; other recent studies have linked older fathers to an increased risk of miscarriages, and to children with schizophrenia or autism.

The theory linking paternal age with an offspring’s health rests on the genetics of aging sperm. Spontaneous mutations can accumulate in the genes of a man’s sperm cells as he ages. These cells divide as many as 660 times by the time a man reaches 40, by some estimates. Each division increases the risk of acquiring a harmful mutation from erroneous gene copying, the theory holds [Science News]. Women are born with their full complement of eggs already in place in the ovaries, and therefore don’t have to worry about increased genetic errors as they age.

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A broad study of couples seeking fertility help has shown that men are not immune from the ticking of the biological clock: They become less fertile after the age of 35. Researchers at a French fertility clinic studied over 12,000 couples who sought treatment at the clinic, and found that older men were less likely to conceive a child with their partners, and were more likely to conceive a child that ultimately miscarried.

Yves Ménézo, an embryologist involved in the study, says the researchers didn’t look for the cause of the would-be fathers‘ declining fertility. But researchers believe that as men age, genetic defects build up in their sperm. In younger men, the damage is minor and can be repaired inside the fertilised egg. But in older men the amount of DNA damage can overwhelm the body’s natural repair mechanisms. “We think there’s a critical threshold of DNA damage and above that, the damage can no longer be repaired. When that happens, genetic mistakes get through to the embryo and you get an increase in miscarriages,” Ménézo said [The Guardian].

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