Scientists discover 2 new 'ghost' lineages that contributed DNA to modern humans

Key Points:

• A new study published in Science reveals traces of two previously unknown "ghost lineages" of extinct human populations embedded in the genomes of present-day humans, one of which is found in all modern humans and dates back about 800,000 years.
• The researchers developed a novel genealogical method to analyze over 500 human genomes, allowing them to detect ancient DNA sequences without relying on fossil DNA, overcoming limitations due to scarce ancient samples.
• One ghost lineage, possibly Homo heidelbergensis, contributed about 0.5% to 1% of DNA in all modern humans, indicating interbreeding in Africa over 50,000 years ago; another "super-archaic" lineage, dating back nearly 2 million years, was found in Oceanian populations likely via Denisovan ancestors.
• These findings underscore that human evolution involved extensive hybridization among multiple hominin species, with introgressed DNA particularly prevalent in genomic regions related to immune and metabolic functions, suggesting adaptive benefits.
• The study's new method offers potential to uncover more ghost lineages, especially from underrepresented regions like Africa and South Asia, and can be applied to study evolutionary histories in other species lacking fossil DNA.