A new computational method has identified DNA segments from two previously unknown ancient human lineages preserved within the genomes of living people.

Researchers at the University of California, Berkeley, have developed a new method to identify DNA from extinct human lineages in modern populations. The study suggests that nearly the entire genome of one 'ghost ancestor' is preserved in small, widely distributed fragments across all living humans. This approach allows scientists to study ancient groups even in the absence of fossilized DNA evidence.

Methodology and Findings

The research team constructed 'family trees' for parts of the human genome, a technique that has only recently become computationally feasible. By applying this method, they identified DNA from two distinct ghost lineages. One ancestor split from the modern human lineage approximately 800,000 years ago, while a second, 'super-archaic' ancestor diverged about 1.8 million years ago.

Evolutionary Implications

Modern humans carry between 0.5 and 1 percent of DNA from the more recent ghost ancestor, which researchers believe likely lived in Africa. The team suggests this group could be Homo heidelbergensis. The older, super-archaic lineage appears to have interbred with Denisovans in Eurasia, with those segments subsequently passed to modern humans. Unlike Neanderthal and Denisovan DNA, which shows evidence of selection against certain regions due to detrimental mutations, the DNA from the more recent ghost ancestor appears to have been largely neutral or selected for, suggesting a larger ancestral population.