For further information, including the full final version of the list, read the Wikipedia article: Swadesh list.
American linguist Morris Swadesh believed that languages changed at measurable rates and that these could be determined even for languages without written precursors. Using vocabulary lists, he sought to understand not only change over time but also the relationships of extant languages. To be able to compare languages from different cultures, he based his lists on meanings he presumed would be available in as many cultures as possible. He then used the fraction of agreeing cognates between any two related languages to compute their divergence time by some (still debated) algorithms. Starting in 1950 with 165 meanings, his list grew to 215 in 1952, which was so expansive that many languages lacked native vocabulary for some terms. Subsequently, it was reduced to 207, and reduced much further to 100 meanings in 1955. A reformulated list was published posthumously in 1971.