An individual consists of various features which can be generally grouped under two headings: rational and emotional. Rational are qualities like reason, thoughts, consciousness, self-reflection; emotional are feelings, appetites, libido. Both of the groups are important and essential for human beings and usually the best combination is when the two of them are balanced.
I agree with the first part of the statement above which says „in an individual, control of the emotions is an artificial achievement“ as long as by „artificial“ is understood „imposed by the society“. To exist a person with only reason is impossible - emotions are inevitable. Though, the other way round is possible. Total dominance of the emotions has been a fact in the primitive human beings. Example: if a contemporary person feels like eating sweets and orders some but does not have any money he will get into trouble therefore he controls his emotions; but if a primitive person feels like eating fruits he might just simply pick some from a tree and satisfy his appetites - there won’t be any society rules to stop him. Spontaneous behaviour can be observed in small children. Children do not have an idea about society and often they act according to their primary appetites not realising any consequences. When growing up they develop a sense for society and with time they lose their initial spontaneity. Example: when a child sees an attractive ball on the ground it just takes not realising that it is not its. It does it spontaneously and it is excusable. However, if a grown up person does such a thing it will be considered a well thought robbery since an adult is part of the society and is responsible for his/her actions in the face of it.
I would argue with the second part of the statement, though, which says that the spontaneity of the emotions „is the real expression of one’s humanity.“ There is no false expression of one’s humanity. Everything that is expressed is real and reflects the actual essence of the expresser. Controlled emotions are not false ones nor are they deceiving. Controlled emotions clearly elucidate the values of their beholder, for example if one is angry at another person but one suppresses one’s anger and keeps one’s promise towards the other person it could be induced that one is reliable, cherishes friendship or is able to forgive. In this way controlled emotions are a real expression of one’s humanity.
The basic concept in this claim is that emotions are essential for humanity while rationality is imposed by artificial means. What do philosophers think about it? Tomas Aquinas believes that feelings are something bad, negative, sinful. One should ignore or suppress them. They lead to hell or, with other words, to a miserable life after death. The activities one does during one’s life should be well thought and moral. Rationality is what should rule one’s life. Similar ideas on the topic have all Christian philosophers. Th existentialist philosopher Camus took the opposite position and in his book „The Outsider“ developed the idea that emotions in today’s life are suppressed by society. His character was a man that expressed all his emotions in their primal natural shape and had no concerns about what the opinion of society about it might have been. Emotions, according to Camus, are essential for humanity and in an individual control of the emotions is an artificial achievement. A more extreme view in this direction have the Cynics that think that natural self-expression of the emotions and bodily needs lies at the centre of humanness. Epicurists have gone even further to define the purpose of life as pleasure and the best life - as one fulfilled with it. Satisfying all their appetites in the moment they occur, being ruled by the momentary feelings, is how Epicurists see the good life. The statement that „In an individual, control of the emotions is an artificial achievement. Their spontaneity is the real expression of one’s humanity.“ expresses to a great extend their point of view.
In a balanced human being, I think, emotions are as important as reason. They bias the human being and orient it. Emotions are inevitable and everywhere - there cannot possibly be a state of mind of a person in which no emotions are present. This is logical since the goal of people in life is to be happy, and happiness itself, the ultimate purpose, is an emotion. If the aim in human life is a feeling then what part does reason take? Is it simply the means for obtaining happiness? Or is it something more? On the other hand exactly this suppression of the emotions is one of the factors that distinguish us from animals. The availability of reason makes control over the emotions not only possible but also natural for human beings. Spontaneity is important but should be limited to a reasonable measure. Sometimes in order to have more pleasant emotions later one should control the less important ones now. In this way one would create oneself as a balanced human being.