library(rgdal)
library(httr)

tmp <- tempfile()

invisible(GET("http://www.naturalearthdata.com/http//www.naturalearthdata.com/download/50m/cultural/ne_50m_admin_0_countries.zip", write_disk(tmp)))

unzip(tmp, exdir = 'ne_50m_admin_0_countries')

world <-readOGR("./ne_50m_admin_0_countries", 'ne_50m_admin_0_countries', verbose = FALSE)