Scientists at a Tokyo research center focused on child health and development have observed that the male Y chromosome shows signs of degeneration in humans and many mammals, yet life can continue without it. The findings were detailed in a major scientific journal.
Most mammals carry two sex chromosomes, X and Y. Males have the XY pair, while females have XX. The Y chromosome carries genes that help trigger the development of male reproductive organs during embryonic growth, guiding a male birth.
Researchers note that in some species the Y chromosome loses genes and can eventually disappear. The same pattern is seen in humans, indicating a possible future where the Y chromosome is absent, even if life persists for millions of years.
One hopeful note from the study is that two rodent lineages have already shed their Y chromosomes and remain viable. These lineages include voles from Eastern Europe and spiny mice from Japan. New populations of these animals have males and females with only X chromosomes, a surprising twist that challenges prior assumptions about sex determination.
The study shows that numerous Y genes in spiny mice have relocated to other chromosomes. At the same time, a gene formerly tied to the Y chromosome was lost, while other gene sets began to take over its functions.
In humans the Y chromosome is shrinking, a process seen across evolution. This prompts questions about how male development will be secured in the future. Some scientists warn that this shift could have wide implications for humanity, while others point out that species adapt by creating new genetic pathways. If such adaptations arise differently across populations, there could be the emergence of new human lineages. The researchers emphasize that evolutionary change can proceed through alternative genetic routes, reshaping our understanding of sex and development.