By Tim Wigmore
What do Richard Hadlee, Martin Crowe and Brendon McCullum all have in common? Here's a hint. It's the same as Owen Franks, Sam Whitelock and Rieko Ioane.
All of this distinguished sextet of New Zealand cricketers and rugby players had at least one older brother who also represented New Zealand. And all of the younger siblings have won more international caps.
This is in keeping with a trend across sport. When two siblings from the same family both play professionally, the younger one tends to enjoy a better career. When two brothers both play in the Major Leagues, the younger one has been shown to be better in two out of three cases. Similarly, in Test cricket it has also been found that younger brothers tend to enjoy more successful careers.
The little sibling effect is one of the most significant findings in sports science, as Professor Mark Williams and I explore in our new book The Best: How Elite Athletes are Made. Younger siblings are significantly more likely to become professional athletes. If you have a younger sibling, they are probably better at sport than you.
A study analysed athletes in 33 sports in Australia and Canada, comparing elite athletes – who had reached senior international competition - with near-elite athletes, who had reached junior national or senior domestic level. The two groups had the same number of siblings on average. But whether those siblings were younger or older helped predict which athletes went on to be elite. The elite athletes had 1.04 older siblings on average; non-elite siblings had only 0.6 older siblings. So if you have two children, from their birth the younger will, statically, have a far greater chance of being an elite athlete.
The roots of the little sibling effect lie in trying to emulate their older siblings. "He told me I was annoying when I used to follow him around all the time," recalled Ardie Savea of playing with Julian, who is three years older. Sam Whitelock, the third of the four Whitelock brothers, remembered games of family rugby involving "plenty of blood and bruises".
Sir Richard Hadlee's legendary competitiveness was first honed playing cut-throat backyard games with his older brothers - and future New Zealand internationals - Barry and Dayle. It is a story that, while the characters change, has been repeated in future generations.
"When you're playing backyard cricket with the brothers, that's what I always dreamed of doing and playing on the international stage," Henry Nicholls, who has two older brothers - including Willy, the media manager for the Black Caps - has said. Tom Latham, Trent Boult and Lockie Ferguson also played with older brothers growing up.
Because they are born later, younger siblings tend to be smaller, slower and less strong. These very disadvantages in backyard games of cricket and rugby mean that younger siblings learn more. Skill acquisition specialists speak of the optimal challenge point. This is the point at which athletes develop skills at the fastest rate - essentially, when the challenge is demanding and stretches them to develop new skills, without being so onerous as to be impossible to compete in. Playing with siblings a couple of years older is likely to provide this optimal challenge point. The very act of failing regularly forces children to adapt and improve. Older siblings who routinely beat their younger siblings are not pushed in the same way. Think of two friends playing tennis together: the weaker one will improve more.
Playing cricket or rugby with their younger siblings, older siblings will be able to lean on their physical advantages to win. Unable to outhit, outrun or outmuscle their brothers and sisters, younger children need to develop tactics to try and keep up.
Richard Williams, was always convinced that Serena - who was 15 months younger than Venus - would become the better tennis player. To understand why he was right, look at pictures of the two playing as children; Serena is normally two or three inches smaller. So throughout their childhoods playing together, she had to make up this gap with skills, tactics and tenacity. By the time they were adults, Serena was no longer physically disadvantaged compared to Venus - and all the traits she had developed meant that she was a superior player.
As much as they would try to deny it, parents also help their little children by treating them differently to their older children. Parents have been shown to be more relaxed with how they treat their younger children: they are more likely to let them play dangerous sports and tend to allow them to play unsupervised at a younger age, with their elder brothers and sisters often charged with looking after them.
This helps younger siblings on the sporting field. 'Playing up' with their older siblings' friends exposes them to tough competition. Informal play - games in backyards, beaches or the local park - has also been shown to be a crucial predictor in who goes on to be an elite athlete. Such informal games develop players' creativity and ability to think for themselves; little siblings often have more informal play at a younger age.
Younger siblings have a final advantage in the sporting lottery. If their older siblings are good athletes, their parents develop knowledge of how to navigate the local sports system and it is easier for little siblings to get seen by the right people.
While his older brother Jono was attending national under-19 selection trials, Trent Boult was bowling in the nets. Trent impressed a coach - the former New Zealand cricketer Mike Shrimpton - who asked him about his own cricket. Trent said that he wasn't in the Northern Districts under-17 squad; soon after, Shrimpton called Northern Districts, and Boult was selected.
The little sibling effect is a significant trend, not a cast-iron rule. Naturally there are exceptions - Colin Meads was Stan's older brother. An older sibling can be a champion, just as a younger sibling can be a sporting dud.
But the little sibling effect is powerful enough that parents, children and those involved in developing athletes should try and heed its lessons. One is the value of informal play.
Another is the importance of playing up and how this accelerates skill development: a first-born child won't be able to benefit from playing with an older sibling, but playing with older children can replicate some of the advantages. In sport, at least, to be born later in a family is to be born luckier.
Tim Wigmore is the co-author of "The Best: How Elite Athletes Are Made" and a sports writer for The Daily Telegraph. You can buy the book here.