The discrimination against humans in primitive society is similar to that against animals, and they will also migrate because of climate factors. The standard of migration is where there is enough water, food and a suitable living environment. At first, people didn't need clothes, and then they gradually began to wear clothes.
First of all, because of a very important reason, that is survival. When the seasons change, in fact, the hardest time is winter, because the temperature will become very low. At this time, if people want to survive, they must keep warm with clothes. But there was no such material as cotton and linen in ancient times, and primitive people made clothes out of animal fur.
The second is to protect your body from external harm. When living in the wild, we have to face many dangers, whether from other species or some environmental damage. At that time, medical equipment was not so advanced, and only injuries could be guaranteed, and skin could be well protected through clothes.
The last reason is that people are beginning to realize the difference between men and women. Clothes can also play a good role in hiding shame, so clothes will be used to cover more important parts.