In the early centuries A.T., human life expectancies grew longer and longer, and other truly un-ageing sophonts such as AIs and vecs appeared. Some thinkers worried about the consequences of this un-ageing state. How it might, in the future, leave the older sophonts, whose personalities were forged in earlier and perhaps radically different times, unable to adjust to or cope with existence. Spurred on by this, some sophontologists began to work to provide a solution to this problem. In the end, the solution they arrived at was to modify a sophonts neural structure so that their personalities did not become fixed as they matured. Instead, they would remain entirely plastic and able to adapt to changing circumstances, permanently retaining a child-like mental flexibility, though with changes occurring more slowly than in a baseline human child. Only memory would remain constant with time.
Based on the Slearner modification, but far more radical and deep-seated than it, the most radical matter was arriving at an optimal plasticity of the personality of the entity it was applied to. But eventually, some two hundred years after the end of the nanodisaster, it was done, and the first of what became most commonly known as the Willowsoph were born. They were so named because, like the tree of the same name, they would bend before the winds of change rather than resist them, and break. One problem with the earlier Willowsoph was that their adaptability left them open to an increased incidence of personality disorders, emotional problems and identity issues compared to the baseline population. In particular, many suffered from extreme problems during adolescence, when the already-significant turmoil of growing up was enhanced by the modification. However, given their adaptability, they also proved to be able to cope with and adapt away from these problems more easily than sophonts without their modification. Later generations of the modification were adapted to engineer out the incidence of these problems. Since then, the clade has spread widely, although many people do not like the idea of their personalities changing with time, and would rather cope with longevity by other means.
Because of this, the Willowsoph modification remains more popular as something emplaced in the mind of an entity by choice, as an adult, rather than something that is inherited. It has also spread beyond hu, into all types of sophont. In general it is most widely taken in places where there is a great deal of change, where the long-lived do find society passing them by if they do not take measures to adapt to its changes. The rate of change of personality in a given Willowsoph depends on their environment. In a stable environment they will still change, but slowly, their personalities taking centuries to shift out of all recognition. In higher pressure environments changes will be correspondingly faster. The modification seems to be quite effective. Willowsoph remain as some of the oldest sophonts, though they are now, in general, people utterly unlike their original selves. Willowsophs also show a much higher then average rate of ascension to higher toposophic levels.
Over the millennia, Willowsoph have proved to be very susceptible to memetic manipulation, particularly as only a small amount of manipulation, applied for a sufficiently long period of time, can have a major effect on them. However, they are also very likely to survive most forms that are not designed to overtly destroy the sophont, though often with problems before that point is reached. Also, attempting to effectively memetically engineer a Willowsoph in the long term is very difficult as the manipulations are eventually adapted away.
As with many other clades, the milder aspects of the Willowsoph modification have been incorporated into much of the human nearbaseline gene pool, though it has been found that simply staying physically young greatly increases the adaptability of a sophont over that of an ageing baseline. Likewise many - though by no means all - non-hu sophonts have adapted at least some of the Willowsoph modification into themselves. Spread widely across Terragens space and beyond, the adaptability of the Willowsoph means that they tend to get on reasonably well with everyone they meet. In particular, they get on very well with the Soft Ones, whose personalities are also highly fluid and adaptable.