If Vernon Philander was an offspinner, he would be R Ashwin. Or if Ashwin was a naggingly accurate seam bowler he would be Philander. None of their countrymen have reached 100 Test wickets faster than them. They both have phenomenal records in helpful conditions. Ashwin has 121 wickets in 19 Tests in Asia for an average under 23. Philander has 109 wickets in 23 Tests in conditions where the ball seams, in South Africa, England, New Zealand and Zimbabwe, at under 20 apiece.

Take them out of their comfort zones, though, and you see completely different sets of numbers. Ashwin has taken only 24 wickets in nine Tests at an average of 57 outside Asia. Philander has bowled in six Tests in Australia, Bangladesh, Sri Lanka and the UAE for eight wickets at 52 apiece. It was always expected that the great starts they had to their careers would be difficult to sustain, but not that the numbers will be so polarised based on conditions.

They are twins separated by conditions. If they could play for the same team, that team could become unbeatable, lethal both on turning and seaming pitches. Unfortunately they don't, and unfortunately they have this reputation of maximising whatever little help they get from the conditions but become totally ineffective when not.

From the evidence so far, Ashwin has looked innocuous when the pitch does not offer turn. Outside Asia, he has not been able to show the magic of Shane Warne nor the persistence of Anil Kumble. From the evidence so far, Philander doesn't have the swing in the air or the extreme pace for times when there is no movement off the deck.

The Australians even went so far as to suggest Philander sat out a match that was being played on a flat pitch. In February last year, just before the start of a series in South Africa, Warner said of the Philander threat: "I would have liked to see him bowl at Adelaide in that second Test [an epic high-scoring draw] when he apparently hurt his back - and was bowling in the nets three days later."

Later during the series, with Philander pretty much negated, Peter Siddle said: "He's probably a bloke that thrives on conditions, and obviously the batters made the most of it the other day and backed themselves to play with a bit of confidence. A lot of teams have sat back and let him build the pressure on them, which has got him wickets. The way the boys attacked him and approached him the other day, getting off strike and swapping left and right-handers, that puts the pressure back on him rather than him building all that pressure. The boys have learnt how to play him."

Similarly when there is no bite in the pitch, for a major part of Ashwin's young career, batsmen have sat back and milked him. There has been no pressure on the batsmen either through wicket-taking balls or parsimony.

Therefore, it is remarkable that the careers of two vastly different bowlers from two vastly different cricketing cultures have followed a near-identical path: unplayable in helpful conditions and sometimes unselectable in unfriendly environs. Ashwin and Philander average 28 and 22 in Test cricket respectively, they have broken many a record, but they are not certain picks in Tests overseas. Yet they are both crucial to their sides wherever picked.

When India went to South Africa in 2013-14, Philander was under the obvious pressure of doing well when it was expected of him, but Ashwin, too, was supposed to play a big role for India. Be it the support act in the first innings, but also pick up the wickets when the match enters the final exchanges. When the opportunity arrived, when India had four-and-a-half sessions to bowl South Africa out for a historic win in Johannesburg, Ashwin bowled 36 overs without a wicket. India just managed to save the game, lost the next, and Ashwin was sent into exile. He counts this Test as his big disappointment, something he gave himself hard knocks for.

Now the tables have turned. Ashwin will face the burden of expectation. He led India's demolition of Australia in 2012-13. He was also Man of the Series in Sri Lanka earlier this year. He gives India the confidence to ask for pitches that will turn from day one. His absence was crucial to South Africa's win in the ODI series. The pressure created by him makes Amit Mishra and Ravindra Jadeja look more potent. He is in the form of his life. South Africa are saying their contest with Ashwin will decide the series, but are at pains to state they have played him well even though Ashwin has got AB de Villiers the only two times he has bowled to this season. India are trying to deflect that pressure, saying the other two spinners could surprise them if South Africa focussed just on Ashwin.

Similarly, if Philander plays and he should, because Kagiso Rabada is raw, and South Africa need the aggression of Morne Morkel. Philander will be expected to do the holding job with an occasional wicket-taking burst when the ball is new or when overhead conditions give him some movement. It will be a role just as important.

Like Ashwin was expected to allow Zaheer Khan and Mohammed Shami short concentrated bursts, Philander will have to do the same for Dale Steyn and Morne Morkel, South Africa's main weapons. India, on the other hand, will want to make Steyn and Morkel bowl longer spells by not letting Philander bowl economically.

Ashwin has also shown signs that he is on the mend in overseas conditions even though the figures don't yet show it. His bowling in Australia this time was much better than his previous overseas tours. They both want to show they are not fair-wicket bowlers, like the numbers suggest. Ashwin's next big test of proving to the doubters that he can do his job in unhelpful conditions will come later. Philander's is here.