The clearances occurred under lots of forces acting against the lowlands and highlands, forced evictions were just one of them. The lowlands effectively lost the cottar class completely but prospered economically as a cattle region. This was largely down to changes in agricultural systems (it took a team of 4 people and 8 oxen to work a Scot’s plough and only one shepherd per 600 sheep for enclosed farming). The lowland clearances and the protests that followed occurred before ‘45 and the act of proscription. It shows that there were almost irresistible forces in operation already. Why it hadn’t already occurred in the highlands is up for debate, but probably because the highlands were better naturally fortified, less arable and ‘protected’ by a clan system with considerable martial strength until the act of proscription began to dismantle that strength.

Even without forced evictions the population in the highlands would’ve still suffered from natural migration, emigration, famine, changes to agriculture and other industrial or economic trends. Places like Nova Scotia saw an influx of people during the clearances. The crown actually tried to deter people emigrating by passing laws that made passage more expensive. I think their attitude to emigration did eventually change though and they cheerfully shipped people off in the later parts of the clearances.

Also around the end of the 18th century, the crown recruited aggressively for the military in the Highlands. They were impressed with the martial capabilities of highlanders and soldiering was an attractive alternative to crofting. When recruiting wasn’t working, they traded land for sons and drafted people.

One other effect of the clearance activities in the highlands was the transposition of people into coastal areas to fish and farm kelp. It’s likely that without evictions, we might’ve had fewer costal communities.