Create new class instance from class method

class Organism(object):
    def reproduce(self):
        #use self here to customize the new organism ...
        return Organism()

Another option -- if the instance (self) isn't used within the method:

class Organism(object):
    @classmethod
    def reproduce(cls):
        return cls()

This makes sure that Organisms produce more Organisms and (hypothetical Borgs which are derived from Organisms produce more Borgs).

A side benefit of not needing to use self is that this can now be called from the class directly in addition to being able to be called from an instance:

new_organism0 = Organism.reproduce()  # Creates a new organism
new_organism1 = new_organism0.reproduce()  # Also creates a new organism

Finally, if both the instance (self) and the class (Organism or subclasses if called from a subclass) are used within the method:

class Organism(object):
    def reproduce(self):
        #use self here to customize the new organism ...
        return self.__class__()  # same as cls = type(self); return cls()

In each case, you'd use it as:

organism = Organism()
new_organism = organism.reproduce()

why not simply use the copy module?

import copy
organism = Organism()
replica = copy.deepcopy(organism)