Survival of the fittest is a phrase that originated from Darwinian evolutionary theory as a way of describing the idea that species adapt and change by natural selection with the best suited mutations becoming dominant.

It is also a microcosm of the sporting world. Athletes create an illusion of precision via hard work - harnessing technique and talent. As the game evolves, so do the athletes. Cricket, as the others, has evolved with time too. Batsmen have explored new ways of looking to outsmart their adversaries - the bowlers. They have rewritten the well-established edicts of batsmanship.

Bowlers too have evolved by adding a slew of different variations and new kinds of deliveries to keep them in the game. In a subtle way, the game keeps shifting - more like "evolutionary biology". One of the discoveries that has constantly evolved, and also widely debated, is reverse swing.

In the backdrop of the ball tampering saga that has suddenly engulfed the sport - with Australia in the Cape Town Test and Sri Lanka in Gros Islet - the phenomenon of reverse swing and the evolution of the art - some might call it an illicit practice - has come under the spotlight.

What is reverse swing?

With insights from Kiran Vaddi, a Doctoral Candidate in University at Buffalo - "Swing of cricket ball is due to the asymmetry in flow between two hemispheres of the cricket ball resulting in an effective side force. It can be generated by making use of seam of the ball and roughness of the ball surface. Both these properties help to alter the thin boundary layers formed and create asymmetry across the two hemispheres. With the new ball, where there is no bias in terms of surface roughness between the two hemispheres, bowlers can only make use of seam on the cricket ball (conventional swing).

With the old ball, bowlers can make use of both seam and surface roughness bias. Making use of both at the same time results in asymmetry opposite to conventional swing, better known as 'reverse' swing'."

In simple words, when the ball gets older and is worn out, it will start to swing in the opposite direction. Hence in this case, an outswinger's grip will tail into the batsman while an inswinger will move away from the batter.

So how did reverse swing evolve? What about origins of reverse swing?

It is difficult to trace the history of reverse swing, but the first recorded instance could be from the former Pakistan opener, Nazar Mohammad during the first half of the 20th century, recounting how bowlers who generally bowled outswing to right-handers would return for later spells and generate inswing in club cricket in Lahore. During the late 1960s and 1970s, Saleem 'Bobby' Altaf was believed to be a fine exponent of swing bowling with the old ball.

As per Wisden, Altaf found swing in difficult conditions in Australia in 1972-73. In the SCG Test, in particular, he shone brightly by bagging seven wickets (in the match) only for the visitors to crash to 106 all out in the second essay and lose by 52 runs.

In Australia, a few were beginning to understand the idea of exploring swing with the old ball. Alan Connolly, the Victorian, Australian and Middlesex pacer, was one of the early exponents of reverse swing. Connolly began his career as a tearaway but later worked on his fitness, shortened his run-up and turned into a smart operator.

While playing Sheffield Shield games for Victoria in 1970s, the pacer alongside the team's wicketkeeper, Ray "Slug" Jordan, noticed that the old ball was moving around. After going through numerous trials, the pair decided to soak one side of the ball with sweat and saliva. The duo's theory was to weigh one half of the ball. It was later proved that 'weighting imbalance' by wetting one side of the ball doesn't have scientific basis attached to it but the pair of Jordan and Connolly envisaged something that many other pacers had no idea of.

Max Walker, who bowled wrong footed and with a windmill action, learnt the art of reverse swing from his Victorian teammate, Connolly, in 1972-73, and used it to deadly effect in the Caribbean that season by bagging 26 Test scalps. Jeff Hammond, the South Australian pacer, also found swing with the old ball in that series. During mid and late 1970s, the legendary Dennis Lillee was another worthy exponent of the craft.

The Caribbean fast bowlers weren't to be left behind either. Eric Atkinson, the tall Barbados pacer, was a useful exponent of reverse swing way back in the late 1950s and 1960s. Atkinson, known for stamina and long spells, had a fondness for hair products and this caused some kind of suspicion among opposition teams that he was employing hair cream to gain more swing. When Hanif Mohammad cracked his epoch-making 337 in Barbados in the 1958 Test series versus Pakistan, he was wary about Atkinson using hair cream.

It turned out to be an interesting battle between them on the pitch. Incidentally, it wasn't just his swing that troubled Hanif as Atkinson also had the unusual habit of whistling during his run-up, which disturbed the Pakistan opener from time to time. The Barbados pacer could only pick up a couple of scalps in the second innings of that Test despite initially troubling Hanif. He then gave a glimpse of his ability to swing the old ball with an eight-wicket haul (in a match) in the Jamaica Test.

There was also a bizarre incident surrounding John Lever, the Essex pacer, when England toured India in 1976-77. Lever bagged seven scalps in the warm-up match versus North Zone and swung the ball prodigiously, and was subsequently selected for the Delhi Test.

In Delhi, Indian openers had made a solid start, in reply to England's 381, with the ball hardly moving in the air or off the seam. In the 11th over, the ball was changed as the umpires deemed it to be out of shape and Lever found appreciable swing to burst through the opposition's batting order. Within no time, India slid from 43 for no loss to 49 for 4. On the next day, Sunil Gavaskar was dislodged for 38 as Lever finished with astounding figures of 7 for 46.

The fascinating story of Lever generating considerable swing didn't stop there. In the third Test in Madras (now Chennai), after India had composed 262, the English pacers found it extremely difficult to bowl in excruciatingly hot and humid conditions at Cheapuk. Mike Selvey, who was a member of the squad, wrote in The Guardian: "Chepauk in mid-January is a Turkish bath". During the break, Willis and Lever were exhausted.

At that juncture, Lever is believed to have asked Bernard Thomas, a former international gymnast and the set-up's physio, for Vaseline. Lever also played football and had a tendency to use Vaseline on his forehead. With no Vaseline around, a 'Vaseline-impregnated rough gauze' was said to have been used by Lever, which eventually led to drama.

Lever later recalled in Wisden: "I wore the gauze after lunch on the third day, when we had them seven down, but discarded it quite quickly as it didn't really work. I put it behind the stumps, but the umpire [Judah Reuben] picked it up and claimed it had come adrift while I was bowling. He obviously felt there was something underhand going on, and he reported it to Bishan Bedi, India's captain, and then to the Indian board, who leaked it to the press."

The umpires then sent a letter in addition to a piece of gauze to BCCI and noted: "There was every possibility of this greasy substance being used along with the sweat on the ball to retain the shine." The ball also was sent for testing and traces of Vaseline was found. In the end, no action was taken. Bishan Singh Bedi, the Indian captain, though, continued to believe it was a case of 'ball tampering'.

He once said to Wisden Cricketer: "If there had been an ICC in those days, a lot of people in the England camp might have lost their jobs." During the Madras Test, Lever was also greeted with a banner that read, "cheater Lever go home". Incidentally, he visited the stadium again in 2016 as a part of a group of cricket enthusiasts to watch the England versus India Test and was seated in the same stand.

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Until late 1970s, however, reverse swing was mostly an unknown art, practised by only a few, who in turn, had developed theories via trial and error methods. Some credit Farrukh Ahmed Khan, who played nine first class matches, as the one who holds the unofficial patent for reverse swing. There was also Saleem Mir, who played for Punjab Cricket Club, and could bowl reverse swing. However, Sarfraz Nawaz later noted in Peter Oborne's book - Wounded Tiger: A history of cricket in Pakistan: "He [ Farrukh] did not bowl reverse swing but in-cutters. He did not know about reverse swing, or he would have bowled it himself."

Nawaz, who later went on to become one of the finest exponents of the craft instead said: "One day, I shone one side of a very old ball and it swung. It was rough on both sides but I shone one side and it swung towards the shine - it should not have done this." And that was the game-changing moment in the sport's landscape. Nawaz regularly practised at the Mozang Link Cricket Club in Lahore and honed his skills on reversing the ball to take it to an elevated level.

Nawaz largely kept the craft a secret before he was said to have passed the formula to one Imran Khan. The story goes in a 50-over game versus the Windies at Berbice in 1976-77, Imran was perplexed by Nawaz's ability to swing the old ball. Nawaz later told Imran that he would give him insights about the craft in the nets. He kept his promise by displaying the art the very next day. His theory was to ensure the ball would get roughed up on one side and keep the other side weighty with spit and sweat.

As a result, the ball would swing towards the shiny side and impart late swing via speed. Nawaz noted that one could use dry tracks of Pakistan to good effect for reverse swing. He was also one of the first cricketers who would teach his bowling partners and fielders in relation to shining the ball.

His protege Imran turned out to be one of the greatest cricketers to play the game. He wasn't just a great fast bowler but developed his batting to such an extent that he started to bat at No.3. He was arguably Pakistan's finest captain, taking Pakistan to World Cup glory. He was also one of the greatest practitioners of reverse swing.

Wasim Akram extended the boundaries of what could be done with a leather ball. He could veer it early or late; in addition to it, he could seam and cut in and away at angles. Akram could expertly even impart swing and extract seam in one offering to befuddle the best. Just recollect the delivery he bowled to Rahul Dravid in Chennai in 1999.

Imran first gave a glimpse of his ability to reverse the old ball in the MCG Test in 1977 when he bagged a five-wicket haul in the second innings. By the time Pakistan bowled in the second innings, the conditions were such that it had resulted in 'lumps' coming out of the ball and Imran put up a fine show of reverse swing. The result was four victims dismissed via bowled or LBW. In the years to come, LBWs and bowleds would become a trademark mode of dismissal of Pakistan's fast bowlers.

At his peak, Imran terrorised batsmen with reverse swing at rapid pace. The former captain's greatest bowling performance perhaps came in the Karachi Test against their arch-rivals India in 1982. Trailing by 283 runs after the first innings, Gavaskar and Dilip Vengsarkar had given India a semblance of respectability by propelling the visitors to 102 for 1. At that time of the innings, Imran produced a blistering spell of reverse swing as the tourists were reduced to 118 for 7 within no time.

Gavaskar was castled by the one that dipped in late while Mohinder Amarnath was trapped in front. But he reserved his best for Gundappa Viswanath. With the assistance of a strong breeze, he bowled a delivery that seemed to be pitching around the sixth stump line, but dipped suddenly and bent extremely late to remove the off-stump, with a bewildered Vishwanath shouldering arms. Imran snared an eight-wicket haul in the second innings as India were crushed by an innings and 86 runs. The all-rounder, who bagged an astonishing tally of 40 scalps in that series, by then had become a national icon and fans had started to compare his fast bowling with American fighter planes.