What happened to our cousins? Here's the huge difference between us

The study was conducted in collaboration with the Okinawa Institute of Science and Technology in Japan and the Max Planck Institute for Evolutionary Anthropology in Germany. "ADSL is one of the few enzymes that has been affected by evolutionary changes in our ancestors," said Svante Pääbo, a Nobel Prize-winning geneticist involved in the research.

The ADSL enzyme consists of 484 amino acids. Valine is found in position 429 of this chain in modern humans, while alanine is found in Neanderthals and Denisovans. This small difference may have had major evolutionary consequences.

The researchers found that the modern human ADSL variant was more unstable, broke down more quickly in cells, and exhibited lower activity. These findings had also been observed previously in laboratory-grown cells.

WHY ONLY FEMALE RATS?

The new study used genetically modified mice. Female mice with the modern human ADSL gene were more successful than other mice at learning to reach for water with specific light and sound cues. This suggests that the modern variant may have an effect on learning or motivation.

However, this difference was seen only in female mice. No similar change was observed in male mice, indicating the complexity of the behavioral effects. "It's not clear why only female mice gained an advantage," said Izumi Fukunaga.

Researchers note that mutations in the ASDL gene occur at a higher rate in modern human genomes than simply accumulating randomly over time, and that this may have provided an evolutionary advantage. However, despite the benefits of this mutation, it is also known that it can lead to problems such as intellectual disability and language impairments due to ADSL deficiency.

While the findings are promising, paleoanthropologist Mark Collard, who was not involved in the research, noted that these results don't say anything definitive about human evolution at this point. However, he said that such studies in mice could pave the way for future research on the evolution of the human brain and behavior.