Since scientists are mostly all too stubborn to go against our widely believed current theory of evolution
Top 15 misconceptions about evolutionLink
A few that pertain to your word choices of "stubborn", "believed" and "widely" as if it is some controversially weak and untested theory and that scientists choose to believe because they want to, rather than because of the evidence... It's all quite the contrary.
Evolution is a theory about the origin of life
The theory of evolution primarily deals with the manner in which life has changed after its origin. While science is interested in the origins of life (for example the composition of the primeval sludge from which life might have come) but these are not issues covered in the area of evolution. What is known is that regardless of the start, at some point life began to branch off. Evolution is, therefore, dedicated to the study of those processes.
Evolution is ‘just’ a theory
Scientifically speaking, a theory is a well substantiated idea that explains aspects of the natural world. Unfortunately other definitions of theory (such as a “guess” or a “hunch”) cause a great deal of confusion in the non-scientific world when dealing with the sciences. They are, in fact, two very different concepts.
Evolution is a Theory in Crisis
There is no debate in science as to whether or not evolution occurred – there is, however, debate over how it happened. The minutiae of the process is vigorously debated which can cause anti-evolutionists to believe that the theory is in crisis. Evolution is sound science and is treated as such by scientists worldwide.
If you want REAL scientific answers to your inquiry, watch the movie Prometheus. It's bar far the most in depth look at how the origin of man REALLY happened.