It is no secret that a baby's brain grows most rapidly in the first 12 months of life - a critical period of learning for any child.
Yet as Archie Harrison Mountbatten-Windsor celebrates his first birthday today, the Duke and Duchess of Sussex can reflect on a more remarkable year of firsts for their firstborn than for many.
So much has happened since Harry and Meghan first presented their 2-day-old son to the world in St George's Hall at Windsor Castle, revealing how the 7lb 3oz infant had a "sweet and calm temperament".
What has followed has been a succession of firsts for a family of three, intent on breaking the royal mould at every turn.
The first mixed-race child to be born to a senior member of the royal family in centuries (it is thought George III's wife, Queen Charlotte, may have had African ancestry), Archie's arrival, at 5.26am on May 6, 2019, was hailed as emblematic of culturally diverse, modern Britain. His dual citizenship of the United Kingdom and of the United States was another first for the House of Windsor.
Even the announcement of his name - meaning "genuine", "bold" and "brave" - was novel, posted by his parents on Instagram alongside a touching black and white picture of them showing him off to the Queen, Prince Philip and Meghan's mother, Doria Ragland.
Ordinarily, royal children are given a plethora of middle names reflecting their ancestry, but Archie was simply given one - Harrison - meaning "son of Harry".
Although they followed in the Princess Royal's footsteps by refusing HRH status for Archie, it surprised royal watchers when the Sussexes also declined the use of the Earl of Dumbarton, one of Harry's subsidiary titles - insisting that the seventh-in-line to the throne be referred to as Master Archie Mountbatten-Windsor.
Another first was the couple seeking to keep Archie's place of birth secret until his birth certificate was published, revealing he was born at London's Portland Hospital - the first senior royal to be born there since the Duke and Duchess of York's daughters, Princesses Beatrice and Eugenie.
Archie's christening, at 2 months old on July 7, also broke with royal tradition. In common with other royal christenings, the "intimate" ceremony happened entirely behind closed doors at the Queen's private chapel at Windsor Castle, with the Queen and Philip not in attendance, having missed Prince Louis' christening the year before. But, unlike other recent services for royals, including the three Cambridge children, the public were not invited to see the happy family and their guests arrive or depart. Instead, the Sussexes shared two photographs of their choice on their official Instagram afterwards.
Harry and Meghan also refused to reveal the names of Archie's godparents - another first. Previous royal christenings had generally seen the palace announce the names of the family and friends entrusted with the infant's spiritual wellbeing. The godparents are unconfirmed to this day, and are thought not to include any members of the royal family.
Just two months later, when he was only 4 months old, the couple took Archie on his first royal tour to South Africa - marking the youngest age a royal baby has ever been taken on an official overseas visit. Prince William was 9 months old when he accompanied Prince Charles and Diana, Princess of Wales to Australia and New Zealand in 1983. Prince George was the same age when the Duke and Duchess of Cambridge took him to Australia and New Zealand in 2014.
It was while they were in Africa that the seeds were sown for Harry and Meghan's subsequent split from The Firm. Archie's presence on the tour - including a meeting with Archbishop Desmond Tutu - ended up being overshadowed by an interview the couple gave to ITV news anchor Tom Bradby laying bare their unhappiness. "It's not enough to just survive... you've got to thrive," Meghan remarked, as she revealed she was struggling to maintain the "British stiff upper lip" in the face of tabloid criticism.
Eyebrows were raised in November, when the Sussexes declined to spend Christmas with the Queen and other royals at Sandringham, opting instead to take a sabbatical to consider their future, amid growing reports of acrimony between the Sussexes and the Cambridges.
After flying to spend Archie's first Thanksgiving with Doria in Meghan's native Los Angeles, the trio then travelled to Canada for six weeks of "family time". Having lived at Frogmore Cottage in Windsor, and travelled to South Africa on tour, following summer holidays in Ibiza and the South of France, the nomadic 7-month-old spent the festive season on Vancouver Island.
Yet it was not until the couple's return to the UK that arguably the most unprecedented events in Archie's life began to unfold. In announcing their intention to step down as senior royals on January 18, Harry and Meghan became the first royals styled HRH to request quasi-royal status in their bid to continue supporting the Queen while seeking financial independence in North America.
It soon became apparent that Archie would become the first royal baby in the immediate line of succession to emigrate. Although they initially returned to Canada, the Commonwealth country that shielded them from the spotlight during their sabbatical, it was not long before California loomed large as the Sussexes' final destination.
In yet another first, Harry and Meghan announced soon after their relocation to LA that they would be launching a new non-profit organisation named after their son. Having drawn up proposals for a vast and ambitious array of projects under the name Archewell, derived from the Greek word for "source of action", the couple revealed that it was the inspiration behind their first born's name.
They explained to the Daily Telegraph last month that they wanted "to do something of meaning, to do something that matters". With the coronavirus outbreak having overshadowed the relaunch, necessitated by the couple losing their "Sussex Royal" branding, it remains to be seen what more firsts Archewell will bring about.
In the meantime, there is the small matter of a "second" baby, according to insiders. As Harry and Meghan continue to house hunt in the exclusive Pacific Palisades neighbourhood, tucked between the Santa Monica mountains and the Pacific Ocean, they are thought to be considering expanding their family.
According to etiquette expert and Pasadena tea room owner Edmund Fry, 80, who famously briefed Meghan on how to behave in royal company, she "absolutely" wants to have another child.
"She is American and Harry is British, both proud of family and heritage," said Fry, owner of The Rose Cottage in the north of LA, where Meghan has been a guest. "They have one child born in England and she wants one born in this country."
Last August, Fry was the first to confirm that the Sussexes were looking for an LA home away from £4 million Frogmore Cottage in Windsor, and one of the first to publicly reveal that Harry and Meghan would return to live there full time before Christmas.
Could an LA-born brother or sister now be on the cards for Archie? That would certainly be another first for the royal baby who has been blazing a trail since birth.