Month: October 2019

Enlarge / Aerial view of the Amazon rainforest, near Manaus the capital of the Brazilian state of Amazonas, Brazil. (credit: Neil Palmer/CIAT)

In Brazil, the rapid deforestation of the Amazon has been accompanied by a rise in malaria. But did the deforestation help increase malaria rates? Or is something more complicated going on?

Researchers Andrew MacDonald and Erin Mordecai think there is in fact a more complicated story at play. In a paper published in PNAS last week, they report evidence suggesting that deforestation does lead to a rise in malaria—but that at the same time, a rise in malaria reduces deforestation. The complicated relationship makes the effects difficult to tease out of the data. And together, the two effects mean that conservation and human health go hand in hand—what's good for one is good for the other.

Confusing evidence

Because malaria is spread by mosquitoes, it would be easy to think that humans have little to do with its prevalence if we're not killing mosquitos. But because human land use leads to habitat change for disease vectors like mosquitoes, human activity can dramatically change the risks of vector-borne diseases.

Enlarge / Lee Shi Tian pumps his fist during an interview in which he highlighted the ongoing protests in his native Hong Kong.

Magic: The Gathering pro Lee Shi Tian used a major win at this weekend's Mythic Championship V event in Long Beach, California as a chance to call attention to protesters in his native Hong Kong.

"Life has been very tough in my hometown in Hong Kong," Lee said in an emotional, livestreamed post-match interview after reaching the Top 8 in the digital Magic: The Gathering Arena event. "It feels so good to play as a free man" he added later.

Lee wore a dark red scarf as a mask over the lower half of his face during the match and interview, because "we wear [masks like that] when we go on the street," as he told Magic site Hipsters of the Coast. Lee also covered one eye during his entrance to the tournament, an apparent show of support for a nurse who was hit in the eye with a beanbag during a recent protest in Kowloon.

Global map of Denisovan gene frequency in modern human genomes (credit: Image courtesy of Jacobsson and Skoglund/Proceedings of the National Academy of Sciences)

University of Washington geneticist PingHsun Hsieh and his colleagues found Neanderthal and Denisovan versions of some genes in the genomes of people from Melanesia. These versions have several thousand base pairs of DNA that have been duplicated or deleted in the normal human versions. Most of this altered DNA is in or near genes related to metabolism, development, the life cycle of cells, communication among cells, or the immune system.

Those gene variants are surprisingly common among Melanesian peoples, and that could mean that their effects were useful enough that natural selection favored passing them along.

DNA from the Denisovans

As Homo sapiens first ventured beyond Africa, they encountered other hominins already living in Europe and Asia, and those encounters left their mark on our modern genomes. Most people from outside Africa carry a little Neanderthal DNA (it makes up about one to four percent of the average non-African genome), and some people from East Asian, Melanesian, and indigenous Australian populations also have a bit of DNA inherited from Denisovans (about one to five percent of the average genome; it’s highest in Melanesian and indigenous and Australian people). Some of that DNA probably stuck with us for tens of thousands of years because it somehow helped our species adapt to new environments and challenges.