Easy. It works and leads to progress in every field related to biology. No other theory of how biology works even comes close to the success of evolution.
Some "evolutionist" scientific achievements since 1955 -
1955: Salk Polio Vaccine
1961: Sabin oral Polio Vaccine
1961 Crick, Brenner et al discover that three nucleotide bases are needed to code for amino acids, confirming a suggestion by nuclear physicist George Gamow.
1963 Effective measles vaccine.
About 1964 Har Gobind Khorana and others work out the genetic code.
1969 Arber and Meselson confirm that restriction enzymes cleave DNA.
1969 Rubella vaccine.
1971 Measles, mumps, rubella combination vaccine.
1972 Berg produces the first artificial recombinant DNA molecules.
1973 Boyer and Cohen make the first transgenic organism.
1978 Riggs and Itakura make the first genetically engineered insulin.
1978 Fred. Sanger et al publish the dideoxy chain termination analysis of DNA.
1980 Frank Fenner oversees the eradication of smallpox.
1980 Robert Gallo et al identify the first human retrovirus.
1983 Recombinant insulin placed on market.
1988 Kary Mullis et al publish the polymerase chain reaction.
1988 Richard Lenski begins long term Escherichia coli experiment.
2000 Craig Venter et al publish a rough draft of human genome.
2005 Rough draft of chimpanzee genome published.
2006 Final draft of first human genome project completed.
2007 Horse genome completed.
2007 Anti-herpes vaccine.
2012 Richard Lenski's long term experiment continues, having demonstrated evolution of citrate metabolism in E. coli.
Thousands of patents in various forms of biotechnology outlining useful or potentially useful inventions.
Creationism leads no where.
Matthew 7:16 , look it up, it applies here.
What is useful about Creationism?
"Young Earth creationist leaders are careful to do no actual science. This is indicated by the scarcity of patents with their names as inventors in any field of biotechnology or medical research. They never discover anything, they never invent anything. By contrast, genuine scientists in these fields have tens of thousands of patents spread across a wide range of topics.
Young Earth creationist leaders only preach to the public, they know if they tried to preach to the biotechnology, agrochemical, pharmaceutical, oil and mining industries among others they would be hurled out on their ears.
All young Earth creationists leaders are completely deluded or fraudulent and their followers have the insane idea that virtually all astronomers, cosmologists, planetary scientists, geologists, physicists, chemists, biologists etc in every country of the world are conspiring against a minority of mostly American sects." - Brigalow Bloke
Put another way: If you wanted to be a medical researcher, what college or university would you attend that had a Biology Program based on Creation Theory?
Missing Links (correct term is "Transitional species") ? We know of thousands, in many species. Consider: What do you think Homo erectus was? Human? Ape? A transitional species (a missing link!) in human evolution?