Biologists hotly debate whether the significant evolutionary changes that led to jawed vertebrates, from hagfish to humans, are connected by ancient gene duplications hundreds of millions of years ago.
—
Carrie Arnold
Contributing,
Quanta Magazine,
2 Sep. 2026
Although people sometimes use animals informally to mean only vertebrates (animals with backbones) or even just mammals, in biology the term includes insects as well.
—
Encyclopedia Britannica,
Encyclopedia Britannica,
14 Aug. 2026
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