Apsychologist who has studied emotions with paul ekman for decades is going to present a summary of the research. which title might this psychologist consider?

The answer is "How Facial Expressions Communicate Emotions".

We know facial expressions pass on emotions. Key facial expressions are generally perceived as communicating particular sentiments or feelings, regardless of whether you are youthful or old, from the city or nation, from created countries or the untamed wilderness. 
We shape impressions of the general population we experience. We take in their stance, their stride, their signals, and we see their outward appearances. All add to passing on their vitality levels and their emotions.

The changes to agriculture in the united states since 1900 is that increased mechanization has increased food production, thereby increasing the need for labor. there has been an increased need for higher speeds of food production due the fact that the population in the united states continues to rise.