What is a process by which organisms with characteristic suited to the environment will survive and reproduce

According to Charles Darwin's theory of Evolution by natural selection, organisms that possess heritable traits that enable them to better adapt to their environment compared with other members of their species will be more likely to survive, reproduce, and pass more of their genes on to the next generation.

(n.d.). Retrieved from http://www.nas.edu/evolution/Definitions.html

One word Adaptation:

he forelimbs below belong to four species that descended in a direct line from the ancestral mammal shown above. of the four descendants shown, which species most likely appeared earliest in evolutionary history?