Study finds most modern human DNA is shared with ancient human ancestors

Neanderthals have been extinct for an extremely long time, but some modern humans carry genes from Neanderthals. Currently, methods used to detect the Neanderthal genes within the human genome use a pattern of linkage disequilibrium or direct comparison to Neanderthal genomes. The challenge for researchers is that those methods are limited in sensitivity and scalability.

A new study has described a new ancestral recombination graphic interference algorithm that can scale to large genome-wide data sets. The algorithm has demonstrated its accuracy on real and simulated data. Once researchers have that data, they generate a genome-wide ancestral recombination graph that includes human and archaic genomes. From that graph, scientists generated a map with human genomes of archaic ancestry and genomic regions not shared with archaic hominins by admixture or incomplete lineage sorting.

The project found that only 1.5 to 7 percent of the modern human genome is uniquely human. That means the remainder is shared with our ancient relatives. In the study, the team also found evidence of multiple bursts of adaptive changes specific to modern humans within the past 600,000 years. Those changes involved genes related to brain development and function.

The study was published in Science Advances on July 16, 2021. Authors of the study include Nathan K. Schaefer, Beth Shapiro, and Richard E. Green. The scientists note in their study that archaeological evidence has reported human remains with many modern features but featuring archaic cranial morphology. That finding suggests that not all human-specific traits arose at the same time.

The team also notes that other studies found the accumulation of derived morphological features in humans happened in three distinct periods. Those morphological boundaries correspond roughly to the timing of the mutational bursts discovered in the new study.