SCIENCE REPORT

Reproductive oddity leads to semi-identical twins

At the first ultrasound, Dr. Nicholas M. Fisk could tell he was looking at identical twins, made obvious by their shared placenta. But at the next ultrasound a couple of months later, he found himself perplexed by what he was seeing: one boy and one girl, sharing a single placenta.

It shouldn’t have been possible, but the fetuses at the Royal Brisbane hospital in Australia were neither fraternal nor identical. They fell into a third, rare category known as semi-identical or sesquizygotic twins, according to an article in the New England Journal of Medicine.

Although it would take several years to prove, they eventually became the first set of semi-identical twins to be identified during pregnancy. They are about 75 percent identical, Fisk says, which he suspects was the result of single egg being fertilized by two sperm before dividing.

Model shows waterfalls may form themselves

Despite waterfalls’ furious unstoppable power, there is a long-standing assumption that they can form only when permitted by other natural forces like tectonic movements, sea level changes and rock transformations.

But this paradigm may be about to change. By building a scaled-down river in a laboratory at the California Institute of Technology and observing the way erosion happens on an uneven slope, a team of researchers demonstrated that waterfalls can sometimes bring themselves into existence without any outside help.

By better understanding how waterfalls can form, the new study, published in Nature, might prompt scientists to reconsider how our planet shaped itself.