As a statistician, I can offer a calculation: if we assume that meteor strikes are random and independent and follow a Poisson distribution with a mean of one per 100 years, then the probability of a strike in any given year is about 1 percent irrespective of recent strikes.
West Amwell, N.J.
THE “GIF” OF LAUGHTER
I enjoyed “The Strange Magic of Micro Movies,” by David Pogue [TechnoFiles], but Pogue discounts the human contribution to why “micro movies” such as GIFs and six-second Vine movies are so popular. The primary use of micro movies I've seen is to communicate emotion or a reaction to a situation, comment, picture or otherwise previously uploaded statement. One could communicate emotions through words or emoticons, but micro movies allow for a more profound message.
Furthermore, while GIFs are used to communicate many emotions, they are typically made with the additional intention of making individuals laugh. I have read multiple theories that state laughter has allowed our species to form larger and more connected social networks. What if these micro movies are the next revolution in such communication?
Edwin E. Rice IV
According to “Human Hybrids,” by Michael F. Hammer, modern humans and extinct archaic human species such as Neandertals were able to create fertile offspring. Doesn't this make modern humans and Neandertals part of one species?
Hammer notes the open question as to how Homo sapiens replaced Neandertals and shows that it is likely that some contemporary non-Africans received an antiviral stretch of chromosome (STAT2) from H. sapiens interbreeding with Neandertals. Is it possible that modern humans wiped out Neandertals by bringing viral disease with them (such as when Europeans “conquered” the New World) and that the reason why modern humans carry STAT2 is that only those Neandertals that had it survived long enough to mingle significantly with the virus-laden newcomers?
HAMMER REPLIES: Regarding Tait's question, although some paleoanthropologists believe Neandertals should be classified as a separate species of Homo, many still regard them as a subspecies of Homo sapiens. Opinions on this correlate with views on whether anatomically modern humans (AMH) originated via Replacement or via Assimilation and Hybridization. Many other mammals that diverged as recently as Neandertals and AMH are considered distinct species but can interbreed and produce fertile offspring.
While McAfee's idea is interesting, in all likelihood, AMH from Africa were more vulnerable to the novel environmental pathogens they encountered as they moved into Europe than Neandertals were to pathogens from the African migrants. In contrast to the Europeans who came to invade the New World, early AMH from Africa probably carried comparatively few pathogens because they would have lived in small hunter-gatherer groups with far less density than agricultural populations that formed tens of thousands of years later and with none of their exposure to pathogens from domesticated animals. People today probably retain STAT2 and other immune-related variants acquired from Neandertals because that DNA helped those early AMH from Africa survive new habitats.
“My Boss the Robot,” by David Bourne, should have referred to Bourne as principal systems scientist at the Robotics Institute of Carnegie Mellon University.