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)

What about something like this:

class Organism(object):

    population = []

    def __init__(self, name):
        self.name = name
        self.population.append(self)
    def have_one_child(self, name):
        return Organism(name)
    def reproduce(self, names):
        return [self.have_one_child(name) for name in names]

Result:

>>> a = Organism('a')
>>> len(Organism.population)
1
>>> a.reproduce(['x', 'y', 'z']) # when one organism reproduces, children are added
                                 # to the total population
                                 # organism produces as many children as you state
[<__main__.Organism object at 0x05F23190>, <__main__.Organism object at 0x05F230F0>, <__main__.Organism object at 0x05F23230>]
>>> for ele in Organism.population:
...     print ele.name
... 
a
x
y
z
>>> Organism.population[3].reproduce(['f', 'g'])
[<__main__.Organism object at 0x05F231D0>, <__main__.Organism object at 0x05F23290>]
>>> for ele in Organism.population:
...     print ele.name
... 
a
x
y
z
f
g