During the warm season, take a drop of pond water, watch the paramecia (a common single-celled Protozoa, which is considered the most ancient group of life-forms in the world) swimming under microscope. What you will see is that most of them swimming randomly and rapidly,
-sometimes, two of them will meet, head to head (if you call the contact portion 'head') for about 1 or 2 seconds then they just separate and swim to different directions, and may never contact again in their short life time;
-occasionally, two of them meet, they contact for 1 or 2 seconds, but after that they dont separate, their memberanes start to fuse, their cell contents meet, then they exchange their cell contents(mostly genetic information) and finally they separate, and may never contact again.
Can you see any similarities in human being?
Let's talk about your question:
The higher level a animal is, the more complicated the ways through which it interacts with its surroundings and other individuals.
Emotion, is a word for human most of the time. If you really trying to fit this word onto other animals, maybe the emotion for paramecia is the '1 or 2 seconds contact'.
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