A Fertility Treatment's Flaw Scientists have found the first direct evidence that an increasingly popular fertility treatment for men can lead to the birth of infertile sons.
The treatment, intracytoplasmic sperm injection (ICSI), involves injection of an individual sperm into an egg in a laboratory dish and transfer of the resulting embryo into the mother-to-be. Since its introduction in 1992, ICSI has helped thousands of men with very low sperm counts or inactive sperm sire children. But because ICSI doesn't depend on millions of healthy, aggressive sperm competing for the egg, as occurs with standard in vitro fertilization (IVF), some experts have been concerned that the technique may result in a defective sperm getting bumped to the head of the class.
In fact, researchers have found indirect evidence that men with chromosomal or genetic abnormalities have, through ICSI, passed those abnormalities to their male offspring. Now David Page and his colleagues at the Whitehead Institute for Biomedical Research have proven the point. They conducted molecular studies of three ICSI sons born to men whose infertility was caused by a missing bit of genetic material on their Y chromosomes. The sons have the same exact deletions and will probably be infertile too, they report in the July issue of Human Reproduction.
Why Plants Deserted the Sahara
The Sahara stretches across North Africa, a vast wasteland devoid of vegetation. But thousands of years ago the area was rich with vegetation, covered in grass and shrubs.
Now a team of German researchers has concluded that this dramatic transformation was triggered by subtle changes in Earth's orbit, which resulted in changes in the planet's atmosphere, sea ice and vegetation.
Martin Claussen of the Potsdam Institute for Climate Impact Research and colleagues used a computer model to analyze the effects of climate changes over the past several thousand years.
The researchers conclude that the transformation occurred in two major episodes. The first less severe episode began between 6,700 and 5,000 years ago while the second much more severe episode lasted from about 4,000 to about 3,600 years ago. Summer temperatures increased sharply and precipitation dropped.
The changes were initiated by alterations in Earth's tilt, which went from 24.14 degrees to 23.34 degrees, and in Earth's perihelion, the point in orbit closest to the sun, which shifted from the end of July to today's early January.
"Our simulations suggest that Saharan desertification, the largest change in land cover during the last 6,000 years, was a natural phenomenon as it can be described in terms of climate-system dynamics only," the researchers write in the July 15 issue of the journal Geophysical Research Letters. "Although humans lived in the Sahara and used the land to some extent, we hypothesize that ancient land use played only a negligibly small role in . . . Saharan desertification."
A Camera Sees in 3 Dimensions
Inventors in Illinois say they've developed a new type of camera that takes three-dimensional images.
The images are not holograms, which are produced with a laser beam, but can be viewed in three dimensions on a computer screen, according to David Brady of the University of Illinois at Urbana-Champaign.
Brady and his colleagues developed the new camera, which takes advantage of technology known as computer tomography (CT), which is already used to make images inside the body, and interferometry, which astronomers use to image distant objects.
The camera works by bouncing cones of white light off all points on the surface of an object and onto a sensor array hooked up to a computer program, which analyzes the pattern of light intensity to determine the exact location of each point and reconstruct the object.
The approach may provide new ways for studying cells and conducting other scientific research, the scientists write in describing the technique in the June 25 issue of the journal Science.
Adapting Ears to Blindness
Research has suggested that blind people compensate for their lack of vision with superior hearing abilities. New research provides clues to exactly how blind people hear better than those with normal vision.
Brigitte Roeder of the Philipps University in Marburg, Germany, compared eight people who had been blind from birth to eight people with normal vision who were blindfolded. The blind people were much better at identifying the location of sounds in space, but only when the sounds were on the "periphery of the sound space."
The researchers also found differences in brain activity between the blind and sighted people, suggesting that the blind people's brains had changed to provide the improved hearing ability, according to a report in the July 8 issue of the journal Nature.
CAPTION: Computer tomography allows the new camera todisplay three-dimensional images on a computerscreen, such as this picture of a toy dinosaur.