Chewing gum had been sold commercially throughout the 1800s
: Mary Bellis, “How
We Have Bubble Gum Today,” ThoughtCo, October 16, 2017,
https://www.thoughtco.com/history-of-bubble-and-chewing-gum-1991856
.
Wrigley revolutionized the industry
: Jennifer P. Mathews, Chicle: The Chewing Gum of
the Americas, from the Ancient Maya to William Wrigley (Tucson: University of
Arizona Press, 2009), 44–46.
Wrigley became the largest chewing gum company
: “William Wrigley, Jr.,”
Encyclopædia Britannica,
https://www.britannica.com/biography/William-Wrigley-Jr
,
accessed June 8, 2018.
Toothpaste had a similar trajectory
: Charles Duhigg, The Power of Habit: Why We Do
What We Do in Life and Business (New York: Random House, 2014), chap. 2.
he started avoiding her
: Sparkly_alpaca, “What Are the Coolest Psychology Tricks That
You Know or Have Used?” Reddit, November 11, 2016,
https://www.reddit.com/r/AskReddit/comments/5cgqbj/what_are_the_coolest_psychology_tricks_that_you/d9wcqsr/
The earliest remains of modern humans
: Ian Mcdougall, Francis H. Brown, and John G.
Fleagle, “Stratigraphic Placement and Age of Modern Humans from Kibish, Ethiopia,”
Nature 433, no. 7027 (2005), doi:10.1038/nature03258.
the neocortex . . . was roughly the same
: Some research indicates that the size of the
human brain reached modern proportions around three hundred thousand years ago.
Evolution never stops, of course, and the shape of the structure appears to have
continued to evolve in meaningful ways until it reached both modern size and shape
sometime between one hundred thousand and thirty-five thousand years ago. Simon
Neubauer, Jean-Jacques Hublin, and Philipp Gunz, “The Evolution of Modern Human
Brain Shape,” Science Advances 4, no. 1 (2018): eaao5961.
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