The easiest answer to this is the very fact of evolution. Yes..we don't have all the missing pieces. So? This world is 6 billion years old. Look how technologically far advanced we have came since..say oh 1900..one hundred years.
You're talking 4 billion years since life came..ok...some bacteria can reproduce..in hours..HOURS? How many generations do you think were there? Ok..then take say..rabbits? Pigs? It's an extreme amount...look at humans even..A person has a child at 16..that person has a child at 16..that person has a child at 16..over the course of 48 years..3 generations..so..over the course of a 100 years..7 generations..in just one person or couple..Mutations and speciation happens very slowly. There are millions of insects? Why? Because some insects have generations of days..that's 365 generations a year..that means every hundred years you have over 36,500 generations of insects.
Look at the quick evolution of viruses which are an even better example because they do so in early lifetimes.

Human Beings as well as other primates (which somehow do quite spectacularly with our same faults) survive on their intelligence. We also tend to group together (such as elephants and other non predatory animals)

Human beings can create all sorts of evolutions with their own technology which has been developed only over the course of 5 million years..Think about what Nature has had..just on Earth..with over 1,000 times that amount of time.