def comma_replacement(random, population, parents, offspring, args):
    """Performs "comma" replacement.
    
    This function performs "comma" replacement, which means that
    the entire existing population is replaced by the best
    population-many elements from the offspring. This function
    makes the assumption that the size of the offspring is at 
    least as large as the original population. Otherwise, the
    population size will not be constant.
    
    .. Arguments:
       random -- the random number generator object
       population -- the population of individuals
       parents -- the list of parent individuals
       offspring -- the list of offspring individuals
       args -- a dictionary of keyword arguments
       
    """
    offspring.sort(reverse=True)
    survivors = offspring[:len(population)]
    return survivors
