9.1 What are cohesive devices? In the last twenty years or so,some underdeveloped countries have increased their food production.Their populations have at the same time grown faster.The standard of living hasn't improved.The increase in food production has been achieved at the expense of using up marginal lands.There has been no gain in the productivity of land labour.9.1 What are cohesive devices? ⚫ In the last twenty years or so, some underdeveloped countries have increased their food production. Their populations have at the same time grown faster. The standard of living hasn’t improved. The increase in food production has been achieved at the expense of using up marginal lands. There has been no gain in the productivity of land labour