500 and counting, yet on the upswing

James Anderson's early career showed little indication that he would go on to achieve what only five bowlers and two fast bowlers managed before him - 500 Test wickets. After his first 20 Tests, played over four years, during which he endured loss of form, a stress fracture and a remodeled action, Anderson had taken 62 wickets at an average of 39.20. At that point, his average ranked 73rd among 76 England bowlers who had taken at least 50 Test wickets. It was hardly a start that suggested one of the most prolific bowling careers in Test cricket.

Then came what was perhaps the watershed moment in Anderson's career: England sought replacements for their pace-bowlers after the bashing they received in the Hamilton Test in 2007-08. And Anderson responded with figures of 7 for 130 - including a five-for in the first innings - in the next Test in Wellington.

That timely haul marked the beginning of Anderson's growth as a fast bowler. By his 50th Test, he had evolved considerably in terms of repertoire and consistency, which also reflected in his career numbers: 181 wickets at an average of 32.08, an overall improvement in a career bowling average of over seven runs from his first 20 matches. After 50 Tests, Anderson had taken ten five-wicket hauls, two more than any other England bowler since his debut, despite missing almost half the Tests he could have played in that period.

If there is one recurring theme in Anderson's career, it is continuous evolution and that is borne out by the numbers. In his next 50 Tests, Anderson took 203 wickets at an average of 27.72. His bowling average had dropped under 30 for good by the time he had played his 100th Test in 2015. Incredibly, Anderson's career has been on an upswing even after his 100th Test. In the 28 matches since, Anderson has taken 113 wickets at an average of 20.82. This is the best any bowler, with at least 50 wickets, has averaged during this period.

In fact, among bowlers who have played over 100 Tests, no other bowler boasts an average post-100 matches as good as Anderson's. In this regard, that he averages better than bowlers like Glenn McGrath and Courtney Walsh speaks volumes about his quality.

500 wickets into his career, Anderson now seems to have only hit the peak of his prowess. In terms of bowling average, Anderson's best 20-match streak in his career was from the Ashes Test at Edgbaston in 2015 to the final Test of the recently concluded series against South Africa. In this time, he took 81 wickets at an average of 18.76. That is a difference in average of more than 20 runs per wicket when compared with the first 20 Tests of his career, when he averaged 39.20. No other bowler in Test history has had such a big difference between the beginning and the peak of their career.

Admittedly, Anderson is more successful at home than when he is playing outside England. No pace-bowler in Test history has taken as many wickets at home as he has. Outside England, he has taken 171 wickets in 53 matches at an average of 33.46 - almost ten runs more than his average at home. Of the 44 pace-bowlers who have taken at least 150 wickets outside England, Anderson's average ranks 40th.

Like his career, however, his performance in away Tests, too, has improved over the years. Even though he is not as effective a strike bowler when playing outside England as he is at home, he has found ways to make batsmen work hard for their runs. Anderson played 19 of his first 50 Tests away from home and took 52 wickets at an unenviable average of 43.84. In the 23 matches that he played outside England in his next 50 Tests, Anderson improved his average to 31.18 while taking 82 wickets. Eleven of his last 27 Tests have been outside England and in those matches, his average has improved further to 23.91.

Only four of his 22 five-fors have come outside England and none of them have come in the 13 Ashes Tests he has played in Australia. The forthcoming Ashes series will be a good time to add a first to that tally. He could possibly overtake Courtney Walsh's tally of 519 Test wickets by the time the series ends. The odds of surpassing Glenn McGrath's tally of 563 are slightly against Anderson, given he is 35 years old. The chances of him reaching this milestone, however, weren't high either, for no bowler before him who averaged 35-plus after 20 Tests ended up with 500 wickets. Or even 400 for that matter.

Numbers accurate up to England's Test against West Indies at Headingley