Why does my dog spin around in circles before he lays down?
While behaviorists are not certain about the exact reasons, dogs usually spin for the following reasons:
1. Survey their surroundings: Before dogs were domesticated, they would need to keep an eye out for predators before sleeping. Spinning around allows them to quickly see and smell their surroundings before rest.
2. Make a den: In order to make their sleeping spots more comfortable, dogs would have needed to clear tall grass, brambles and rocks. Spinning around would allow the dog to pat down and brush aside any obstacles.

Notice that these reasons are no longer relevant to modern dogs, who usually sleep comfortably inside safe houses. However, the instinct to spin around was trained over millions of years and so continues to affect their behavior
Does humans also have that kind of behaviour traits that are no longer required but still exist ?
Yes, humans also have behaviors that are no longer necessary but still exist as a result of evolution and cultural practices. For example:

Fear Responses: Humans are wired to respond to certain stimuli such as heights, darkness, or loud noises with fear. These responses were once critical for survival, but they can now be maladaptive and interfere with daily life.

Eating habits: Our ancestors had to store food for long periods in their bodies, but in today's world, food is readily available. This has resulted in overeating and food cravings.

Aggression: Aggression was once an essential survival tool, but in modern society it is often seen as a negative behavior.

Sleep patterns: Before the invention of artificial lighting, people had to sleep when it was dark, and wake up when it was light. Nowadays, artificial lighting and modern lifestyles have altered our sleep patterns, but many people still have a natural inclination to sleep when it is dark.

These are just a few examples of behaviors that are no longer necessary but still persist in humans, which can be traced back to our evolutionary history.