Final answer:
The mapping of the complete structure of human DNA in the early 2000s created promise in how scientists understood human biology.
Step-by-step explanation:
The scientific development in the early 2000s that created promise in how scientists understood human biology was a. The mapping of the complete structure of human DNA. In 2001, the completion of the Human Genome Project marked a major milestone in biology. This project involved sequencing all 3 billion bases that make up our DNA and identifying the location of more than 20,000 human genes. This knowledge has allowed for a better understanding of gene function, the identification of genetic disorders, and the development of personalized treatments.