The world is created billions of years ago. The creatures on the earth are of unlimited types. Human is only creatures that have survived in the earth. The remaining creatures find their way hard to maintain their lives.
Most of the creatures were ended up in their growth. The reason I understand the creatures who are no more on the earth may be that God had not given them enough patience. Maybe they were not adequate for the changing environment.
Human is a creature that tends to adapt with the surrounding environment. But this is not the case with all humans. Some humans want to live with old manners. Every human tends to live their lives as they wish. Some humans are smart and others are a little behind.
God has given life to everyone and everyone live their life as they like to live. You have seen many people lose their lives in childhood. And many people are diagnosed with deadly diseases. No one is safe from unknown things happening.
If you are lost then do see some people who are bad condition than you. Maybe your problems are bigger than others. But as you know human is the unique creature that has survived on the earth. God has sent us on the earth for a good life. The problems we see in our daily life is created by ourselves. We have to fight with the problems as we can.