Final answer:
The molecular clock is a method in evolutionary biology that uses DNA or protein differences to estimate the divergence time between species. It supports the African Eve theory, suggesting that all humans share a common maternal ancestor from Africa 100,000 to 200,000 years ago. While powerful, the concept of a precise molecular clock is contested and subject to variability.
Step-by-step explanation:
The concept of a molecular clock is foundational in the study of evolutionary biology. It is used to estimate the time elapsed since two species diverged from a common ancestor by comparing DNA sequences or protein differences. Key to this method is the assumption that genetic mutations accumulate at a relatively consistent rate over time. In the context of human evolution, molecular clocks have been instrumental in supporting the African Eve theory. This theory posits that all modern humans can trace their mitochondrial DNA (mtDNA) to a common ancestor, often dubbed 'Mitochondrial Eve,' who is believed to have lived in Africa around 100,000 to 200,000 years ago.
Scientific investigations employing mtDNA are particularly useful because it is maternally inherited and does not recombine like nuclear DNA, allowing for a clear lineage trace. Research has suggested that mtDNA mutates at a predictable rate, which has been used to pinpoint when populations diverged. This is complemented by studies of the Y chromosome, which trace paternal heritage back to an ancestor living in Africa approximately 140,000 years ago. However, it is important to note that the actual rate of mutation can vary, and the notion of an inflexible molecular clock has been contested.
Refinements to the molecular clock concept could involve calibrating mutation rates based on other evolutionary information, such as the fossil record, or by studying conserved protein sequences in prokaryotes. In summary, while the molecular clock has its complexities and is subject to ongoing debate, it remains a powerful tool in understanding the timeline of human evolution and relatedness among species. Mitochondrial research supports the African Eve theory, suggesting a maternal lineage trace back to a single woman in ancient Africa.