Influx of new talent, guaranteed by departure of six from Govt benches, hard to match as Labour old-timers hang in there for another election.
In any walk of life, ongoing renewal is critical. Any sports team, business or political party, however successful, risks being viewed as stale if it ignores this necessity for too long.
But achieving the input of new blood and fresh ideas can be difficult if incumbents fail to recognise their race is run or fight hints that their time is up.
Hats off, then, to the six National Party MPs, including most lately the former Cabinet minister Kate Wilkinson, who have announced already they will be retiring at next year's general election.
Not only have they opened the door to a strong influx of new talent but they have, by way of contrast, drawn attention to Labour's difficulties in this matter, an issue complicated further by the new quota passed at the party's annual conference.
Labour's gender rule will ensure that 45 per cent of its MPs will be women after the next election, reaching 50 per cent by 2017.
This is a far more sensible arrangement than the previously proposed "man ban", which would have permitted women-only contests for the party's ticket in electorate seats.
The push for guaranteed gender equality has now produced an approach that will satisfy most in the party, even if many in the wider community will see it as verging on political correctness.
Labour sought to leaven that prospect by noting it already had 41 per cent women in its caucus. It would not, therefore, take much to hit next year's target.
Maybe not, but that makes light of the fact that most of the new candidates likely to get high places on the party list or selection for safe electorate seats will have to be women.
Indeed, if Labour were to win 41 seats next year, as suggested by current polling, 19 of its MPs would have to be female, leaving only two of the seven new seats for men.
And that may not be the most challenging aspect of it. The conundrums will mount if Labour appears likely to lose MPs at an election.
The only way to get a substantial intake of new male MPs next year will entail either dumping some sitting male list MPs down to unwinnable places on the list, or pushing electorate MPs to retire from politics to open up more seats.
The finger is, therefore, being pointed at senior Labour figures such as Phil Goff and Trevor Mallard.
Both have indicated they plan to stand again. Indeed, Ross Robertson is the only Labour MP to have so far announced he will leave Parliament next year.
The contrast with their opponent is obvious. It seems National MPs are prepared to retire when they see they have gone as far in politics as they can.
Some may leave with regrets; others will be happy to go. The vast majority, however, seem prepared to go back to the enterprise or profession of their pre-parliamentary days.
Could it be that Labour MPs have tended to regard politics as more of a lifelong career? In the process, they have made their party's renewal more difficult.
The Labour leader, David Cunliffe, says adopting a quota for women is all about "moving towards normality".
Philosophically, the party believes it is important to put this stake in the ground.
Practically, there may yet be some benefit in the immediate future from the added pressure to renew itself.