Friday, March 16, 2012

Climate Change Drives Human Evolution Out of Africa


Stewart and Stringer discuss in Science (subscription required) their synthesis of paleoclimate data with biogeographical data during glacial-interglacial cycles in Eurasia. Combining these data with recent insights from ancient DNA and the human fossil record outside of Africa, these authors put forward an argument that highlights the importance of climate refugia (areas where a temperate adapted species survives through a harsh glacial cycle) in shaping human evolution. Small populations of hominins trapped in refugia would have differentiated by genetic drift and local adaptation, leading to the formation of new species such as H. antecessor and Neanderthals. The authors suggest that this biogeographic model may even explain patterns of interbreeding between modern humans and archaic species which have been inferred from genetic data (e.g.)

Monday, March 12, 2012

Basic Introduction to ggplot2

This is a very basic introduction to the ggplot2 package.  A much more detailed description of the package can be found in this book ggplot2: Elegant Graphics for Data Analysis.

On his website (http://had.co.nz/ggplot2/) package author Hadley Wickham describes ggplot2 as
a plotting system for R, based on the grammar of graphics, which tries to take the good parts of base and lattice graphics and none of the bad parts. It takes care of many of the fiddly details that make plotting a hassle (like drawing legends) as well as providing a powerful model of graphics that makes it easy to produce complex multi-layered graphics.
There are two major functions that you will use in ggplot2
  • qplot() - for quick plots 
  • ggplot() - for fine, granular control of everything (not going to get into this in this post)
Lets start with qplot() to see how easy and pretty things can be with ggplot2.