Observatory: Male Sensitivity Written in the Genes

In human development, certain genes act as master switches, ensuring that we are born with similar attributes (one head, two lungs, 10 fingers) in nearly all circumstances. Such genes tend to be highly reliable and resistant to environmental factors.

But the gene responsible for activating male development is surprisingly unstable, leaving the pathway to male sexuality fraught with inconsistency, a study finds.

The SRY gene on the Y chromosome sets off the growth of male sex organs in human embryos (all of which start out essentially female). To study the gene, researchers at Case Western Reserve University looked at families in which daughters inherited a Y chromosome, a rare occurrence in which SRY fails to fire, leaving a genetically male embryo to develop as a sterile female.

They found that SRY is highly vulnerable to environmental factors, allowing the slightest interruption to significantly alter male sexual development. That leads to a wide divergence of testosterone-related male attributes (among them muscle mass, aggression and genitalia development) from one man to another, according to the study, which was published in The Proceedings of the National Academy of Sciences.

The variability probably serves an evolutionary purpose, said one of the authors, Dr. Michael Weiss.

“This tenuous switch is what underlies the variability of testosterone secretion in utero,” he said, producing men with a wide range of gender styles and capabilities that can help ensure a community’s survival. 

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Observatory: Software That Exposes Faked Photos

Using algorithms designed to sniff out suspicious shadows, computer scientists from Dartmouth and the University of California, Berkeley, say they have developed software that can reliably detect fake or altered photos.

The technique could be useful in the emerging field of photo forensics, said Hany Farid, a Dartmouth computer science professor and developer of the software. In the age of Photoshop, detecting manipulated photos is a growing priority for lawyers, journalists and people involved in law enforcement and national security.

To determine an image’s authenticity, the software uses geometric formulas to detect and analyze shadows that are invisible to the naked eye, then lines them up with a potential light source. If it cannot do so, it deems the image to be physically implausible.

Analyzing shadows is a common technique in photo forensics, said the study, being published in the September issue of ACM Transactions on Graphics. But the eye simply cannot compete with the sophistication of today’s image-manipulation software.

“Perceptual studies show that the brain is largely insensitive to gross inconsistencies in shadows,” Dr. Farid said. “That means that an analyst may not be very good at determining whether shadows are real or not. But more importantly, it means a forger may not notice when he or she places an incorrect shadow on an image.”

To demonstrate the software, the researchers ran an analysis of a picture of the 1969 moon landing. They determined that the image was not a fake. 

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Observatory: 160-Million-Year-Old Fossil of an Omnivore

The fossil, found in Liaoning Province in northeastern China, is the earliest known skeletal fossil of a multituberculate, and offers new insight into this mammal group’s incredible success. Multituberculates thrived alongside dinosaurs for more than 100 million years and then outlived them for 30 million years before becoming extinct, making way for rodents.

The newly described species, Rugosodon eurasiaticus, had highly ornamented teeth, with many wrinkles and creases. This is a sign that multituberculates started out as omnivores, researchers said.

“It has lots of small ridges and grooves that are densely packed,” said Zhe-Xi Luo a paleontologist at the University of Chicago and one of the study’s authors. “In modern rodents this is related to a diet supplemented by small insects and small vertebrates.”

Over time, many multituberculates evolved to become herbivores, an adaptation that helped them thrive. The researchers also discovered that the rodentlike animal had mobile and flexible anklebones, suggesting that it was a fast runner that primarily lived on the ground.

“We paleontologists have always been puzzled by how some of the later multituberculates could jump from the ground and climb up in trees,” Dr. Luo said. “Lo and behold, in this early skeleton we have all those features already.”

The well-equipped ankle also helped multituberculates thrive, he said.

Rugosodon is described in the current issue of the journal Science. 

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