Ecology and evolution of infectious diseasesgenomics"Tree of All Life"global There are many fields of biology, and in some branches, biologists are concerned with tiny , while others study vast . Biologists who study how the activities of all living organisms affect both the atmosphere and climate are working in the field of . Researchers who seek to replace damaged genes or to genetically engineer bacteria are studying . Some biologists work to combine the latest genetic information with computer technology to organize all living things into a single universal . Scientists concerned with HIV, bird flu, drug-resistant bacteria, and other pathogens are researching the , while others who look at the entire sets of DNA code contained in a wide range of organisms are studying .