|MadSci Network: General Biology|
There is no generally-accepted answer to this question. Many criteria for intelligence/sentience/consciousness have been suggested, including: Tool use. (Chimpanzees and some birds make and use primitive tools.) Language use. (The jury is still out on the degree to which various nonhuman animals use language.) Learning / adaptation. (Dogs can learn, and even microscopic organisms can "learn" to behave differently.) You might enjoy the book "The Mind's I", edited by Hofstadter and Dennett, which explores some of the issues involved in this question.
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