Compare a duck billed platypus and a human—what are three characteristics we share and what are two we do not?
The platypus is an interesting choice for comparison to a human, because the platypus is a good example of nature defying our methods of categorizing life.
The platypus and humans are both mammals. The most fundamental definition of this name is that the organism is a warm-blooded vertebrate, gives birth to live young, feeds its young with milk expressed from the mother's body, and is capable of growing body hair or fur.
Humans and the platypus share the traits of being warm-blooded vertebrates with body hair that feed their young with milk, but the platypus reproduces by laying eggs rather than giving birth to live young. Other differences include the fact that the platypus has ten sex chromosomes rather than the two that humans possess (XX for females, XY for males) and that the platypus is naturally found only on the eastern coast of Australia, whereas humans are considered to have originated in Africa and are now "naturally" found everywhere on the planet.
This raises the interesting question of just how accurate the term "mammal" can be; if the platypus doesn't fit all the definitions of the term, does it deserve to be called a mammal? Generally the answer is yes, because the platypus shares more traits with other mammals than not, and its fossil and genetic history indicates that it is a remnant of some of the earliest ancestors of "true" mammals.
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