I managed the one with nature achievement (hard start, harsh weather) with a final population of about 200 to 300, on a large map with education (tried without education it didn't end well for the bannies, they were unable to produce enough tools or firewood to maintain themselves). The amount of time for healthy population growth was long with education, I built a trade center as soon as I reached the achievement but by that point it was to late and while there were undeveloped areas of the map food in developed areas was to scarce to maintain any population, at which point my entire town died, despite recent arrivals of seed.