More than seven billion rolls of toilet paper are sold yearly in the United States alone. Americans use an average of rolls per capita a year. The average American uses 50 pounds (23 kg) of tissue paper per year which is 50% more than the average of other Western countries or Japan.  The higher use in the United States may be explained by the fact that other countries people use bidets or spray hoses to clean themselves.  Millions of trees are harvested in North and South America leaving ecological footprint concerns.  Citizens of many Western countries sometimes use toilet paper for industrial purposes such as oil filters,  which may distort the use statistics.
Some of their findings were expected; for example, longer eggs tend to hatch into larger birds. But their most surprising finding was that flight ability was the best predictor of egg shape; adept flyers laid more elliptical and asymmetrical eggs. Stoddard and her colleagues think that, in order to be aerodynamic, flying birds must have streamlined bodies, which limits the possible width of the egg. The birds still need to produce eggs with enough yolk and egg white inside, though. More elliptical and asymmetrical eggs would maximize the volume contained within an egg of a given radius, making them advantageous for birds of flight.