def stats_file_keys(gene_number):
    """Return fiels in stats file, ordered, as a list of string"""
    return [
            'popsize',
            'genenumber',
            'generationnumber',
            'diversity',
        ] + ['viabilityratio'   + str(i) for i in range(gene_number)
        ] + ['viabilityratioDB' + str(i) for i in range(gene_number)
    ]