Scientists have uncovered a “hidden chapter” in the history of human evolution and it turns out it’s much more complex than previously thought.

It’s known that modern day humans, known scientifically as Homo sapiens, emerged from Africa around 300,000 years ago, but knowledge of what happened before that has been rather sparse.

But now, experts from the University of Cambridge have made a significant discovery that suggests human beings came from at least two different ancestral groups.

The groups, labeled Group A and Group B, are thought to have separated around 1.5 million years ago with the possibility that one ancestral population trekked miles away to a new area.

When those two groups reunited around 300,00 years ago and began breeding is when human beings as we know it were formed, with Group A responsible for around 80 per cent of genetic makeup and Group B, 20 per cent.

The discovery was made thanks to data from the 1000 Genomes Project – “the largest public catalogue of human variation and genotype data” from populations around the world.

While it’s now known that Homo sapiens have two lineages, not one, what experts still don’t know is where exactly this reunification of the groups happened.

Theories vary, but the study’s lead author, Dr Trevor Cousins, believes it’s “likely” that both groups originated and remained in Africa when they diverged.

However, there is some speculation that one group could have migrated to Eurasia while the other stayed in Africa, or vice versa.

“The genetic model can not inform us about this, we can only speculate [but] in my view there are valid arguments for each scenario,” Cousins told MailOnline.

“Due to the diversity of fossils found in Africa, perhaps scenario one – A and B both originated and stayed in Africa – is the most likely.”

Experts also don’t know what ancient species Groups A and B were. According to fossil evidence, species such as Homo erectus and Homo heidelbergensis lived in Africa, and other regions, during the time period.