*The piece originally featured on sport.co.uk* The average length of the modern footballer's playing career is between 15 and 20 years. Most breakthrough around the age of 18 and then continue to play until the age of 33, or in some cases later. Players will naturally have a period in which they are said to be in their 'prime' – at time when they are at their physical and technical peak.Sustaining success, as an individual, across the span of 15 years is a very difficult challenge and is something that many fail to achieve. Age will, inevitably, catch up with everyone and they will become less effective in their position. Injuries will take their toll and eventually players will no longer be able to do what they had once done with such ease.The most successful players, though, are able to evolve their style of play or even their position throughout the course of their career so as to enable them to be as valuable in their mid-30s as they were in their early 20s. When their speed, strength and stamina fades, their game must adapt lest they suffer the fate of many players the wrong side of 30 who slump down into the lower leagues. The acceptance that one can no longer perform in the same way as they did back in their hay-day requires a transformation of their approach to the game. It is Darwinism in action – if you want to survive at the top then you must evolve. This does not mean that every player who plays well into their 30s have undergone this transformation. Players like Teddy Sheringham continued playing in a largely similar style, albeit to a lower standard, until the age of 40. Claude Makélelé's role as the archetypal holding midfielder relied far more on his ability to read the game than cover a lot of ground and as such it is no surprise that this is a role he has been able to continue to do successfully right through his career.The real challenge comes to the once all-action, buccaneering players who, whether it be because of age or injury, have had to change their game. Likewise, other players spent long periods of their career in one position before moving to a new role with equal or greater success. Certain managers and clubs, like Sir Alex Ferguson and AC Milan, have proven themselves particularly adept at helping remould players with great success.10. Danny MurphyFor much of his prime, while at Crewe Alexandra and Liverpool, Danny Murphy played in an advanced, attacking-midfielder role or as a deep-lying forward. His creativity and ability to contribute both goals and assists saw him rise to international level. Since entering his thirties and having left Liverpool to go to Charlton and Tottenham before settling in Fulham, where he is club captain, Murphy's game has been vastly altered. He now dictates his side's passing and attacking play from a deeper role. His new, more disciplined style of play has got the best out of his ability in his advancing years.9. Luis EnriqueThe Spaniard plied his trade on both sides of

read more: Darwinism in Action: The need for footballers to evolve