Natural selection and genetic modification Study Guide

The study of human evolution relies heavily on fossil evidence, which provides a timeline of physical changes in hominins (the group including modern humans and extinct human species) over millions of years. Key fossil discoveries, such as Ardi, Lucy, and various finds by Richard Leakey, highlight critical evolutionary developments. These fossils reveal changes in skeletal structure, particularly those related to bipedalism (walking upright), brain size, and dental characteristics. By comparing these ancient remains with modern human skeletons, scientists can reconstruct the evolutionary pathways that led to Homo sapiens, tracing gradual adaptations to changing environments and lifestyles. The incompleteness of the fossil record means that new discoveries can always refine our understanding of human lineage.

The emergence of antibiotic resistance in bacteria provides a clear, real-world example supporting Charles Darwin's theory of evolution by natural selection. Within a population of bacteria, natural genetic variations exist. Some bacteria may possess random mutations that confer resistance to certain antibiotics. When an antibiotic is used, it acts as a selective pressure, killing off the bacteria that are susceptible. The resistant bacteria, however, survive and reproduce, passing on their resistance genes to their offspring. Over successive generations, the proportion of resistant bacteria in the population increases. This change in the genetic makeup of the bacterial population over time, driven by environmental pressures (antibiotics), aligns perfectly with Darwin's principle of natural selection, demonstrating how species can evolve to better suit their environment, even if that environment includes antimicrobial agents.