Promoting Diversity from a Biological Perspective
It is believed that there are currently more than 30 million different species of living organisms on Earth. Animals cannot produce their own energy to survive; instead, they grow by using the chemical energy produced by plants from sunlight and carbon dioxide. This shows that animals cannot live on their own. The same is true for humans. For humans to survive, a variety of animals, plants, and microorganisms coexist. Furthermore, even if one species were to dominate, the food chain would be disrupted, and that species itself would not be able to survive. In biology, it is thought that species with rich variety at the genome level are the ones that adapt to environmental changes and survive. This has led to the evolution of sexual reproduction, where the genomes of two individuals mix, and meiosis, where two sets of chromosomes cross over to become chimeric.
We who engage in this sexual reproduction are diploid, possessing two sets of genomes: one from our father and one from our mother. In meiosis, synapsis occurs, where chromosomes from the father and mother align and pair up. Having an even number of sets is necessary for the paternal and maternal chromosomes to cross over and become chimeric. Therefore, the established theory is that triploid organisms cannot undergo meiosis because synapsis does not work properly. It was the planarian that overturned this established theory. In one species of planarian, *Dugesia ryukyuensis*, diploid and triploid individuals coexist. Since planarians have coexisting individuals that reproduce sexually and asexually, it was thought that diploid individuals reproduce sexually, while triploid individuals reproduce asexually (parthenogenesis: a method of reproduction where an egg develops without fertilization). However, when my group conducted a parentage test on triploid individuals, we found that the offspring's genes were a chimeric mix from both parents. This indicates that triploid individuals can also reproduce sexually. We discovered that planarians undergo a special type of meiosis. It is thought that triploid individuals also acquired this special meiosis to increase diversity and survive. What do you all think upon hearing about this research? It may not have direct applications for humans, but the phenomena that life weaves are truly a bundle of mysteries.
Recently, "diversity" has also become important in our society. Even in our Faculty of Science and Technology, "Diversity, Equality and Inclusion" has become a key issue. However, living organisms have evolved to increase diversity as their own survival strategy to ensure the continuation of their species, without particularly considering it an "issue." Today, we tend to think that humanity is the sole winner on Earth. By producing vast amounts of food, humanity has disrupted the food chain, and through excessive industrial production, has released large amounts of CO 2 , causing global warming and placing a great burden on the Earth. Originally, living organisms, including humans, evolved by changing themselves to gain diversity. Despite this, humans, a species of living organism, are now in a state where they could end the 3.8-billion-year history of life by drastically changing the environment without changing themselves. I hope that all of you will come to the Department of Biosciences and Informatics to learn about the system of biological development through evolution from real biology, and use that knowledge for the future of the Earth.