What does the part "might equally well have done" mean?

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> Several have defined man as an animal which laughs. They **might equally well have defined** him as an animal which is laughed at. [Source](http://books.google.co.jp/books?id=jeh9WiRIdW0C&pg=PA10&dq=%E2%80%9CThe%20comic%20does%20not%20exist%20outside%20the%20pale%20of%20what%20is%20strictly%20human...%20Laughter%20has%20no%20greater%20foe%20than%20emotion.&hl=en&sa=X&ei=BobHUrDgKcXXkgX7koCACg&redir_esc=y#v=onepage&q=laughter%20of%20a%20group&f=false)
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I can't find this in my dictionary.