President Trump boasted of his accomplishments in his first 43 days in office, comparing the start of his presidency to ...

No.2 pencils are widely used, but you may not know what the number actually refers to. This video explains how pencils developed into their modern form and the significance of the labeled numbers.

In particular, it explains that humans have one fewer chromosome pair in their cells than apes, due to a mutation found in chromosome number 2 that caused two chromosomes to fuse into one.