--- description: Find out why Katsuhiko Hayashi is one of the 100 most influential people of 2024. title: Katsuhiko Hayashi: The 100 Most Influential People of 2024 image: https://static.time.com/v3/assets/bltea6093859af6183b/bltc31836a000720a03/698a559509208f82aa41d062/time-100-2024-katsuhiko-hayashi.jpg?branch=production&width=3840&quality=75&auto=webp&crop=16:9 --- Apr 17, 2024 # Katsuhiko Hayashi by Shinya Yamanaka  Kosuke Arakawa For years, Katsuhiko Hayashi, a professor at Osaka University in Japan, has been at the forefront of developmental and reproductive biology, focusing on turning pluripotent stem cells (which can become any cell) into germ cells—those that become either an egg or a sperm. In just the past few years, he has made several fundamental discoveries. He re-created the entire cycle of a mouse egg cell (oocyte) and reconstituted the ovarian follicle—which holds the egg—in a dish. Last year, his team [produced](https://www.nature.com/articles/d41586-023-03922-6 "undefined") oocytes using cells from male mice, resulting in pups born to two biological fathers. His work offers hope to those with infertility problems or same-sex couples who one day wish to have biological children. It could also enable endangered species to breed. As biological breakthroughs often pose a double-edged sword, Katsuhiko is well aware of the scientific and ethical challenges as he determines whether his discoveries are translatable and socially acceptable for aiding human reproduction. _Yamanaka is a researcher and Nobel laureate_ _Order your copy of the 2024 TIME100 issue_ [_here_](https://magazineshop.us/TIME%5F100 "undefined") ```json [{"@context":"https://schema.org","@type":"Article","@id":"https://time.com/collections/100-most-influential-people-2024/6964621/katsuhiko-hayashi-2/","mainEntityOfPage":{"@type":"WebPage","@id":"https://time.com/collections/100-most-influential-people-2024/6964621/katsuhiko-hayashi-2/"},"headline":"Katsuhiko Hayashi","datePublished":"2024-04-17T10:59:46.000Z","dateModified":"2026-03-03T00:28:58.210Z","description":"","url":"https://time.com/collections/100-most-influential-people-2024/6964621/katsuhiko-hayashi-2/","keywords":["TIME100","franchise","Magazine","Special Project","sponsorshipblock","Accolades","2024TIME100","T100Innovators2024"],"thumbnailUrl":"https://static.time.com/v3/assets/bltea6093859af6183b/bltc31836a000720a03/698a559509208f82aa41d062/time-100-2024-katsuhiko-hayashi.jpg?branch=production&width=1200&quality=75&auto=webp&crop=1200:675&height=675","author":[{"@type":"Person","name":"TIME Staff","jobTitle":null,"url":"https://time.com/author/time-staff/"}],"creator":"TIME Staff","articleSection":"","image":[{"@type":"ImageObject","url":"https://static.time.com/v3/assets/bltea6093859af6183b/bltc31836a000720a03/698a559509208f82aa41d062/time-100-2024-katsuhiko-hayashi.jpg?branch=production&width=1200&quality=75&auto=webp&crop=1200:675&height=675","width":1200,"height":675}],"publisher":{"@type":"Organization","name":"Time","url":"https://time.com/","logo":{"@type":"ImageObject","url":"https://time.com/images/logo.png","width":528,"height":156},"foundingDate":"March 3, 1923","sameAs":["https://www.facebook.com/time","https://www.instagram.com/time/?hl=en","https://twitter.com/time","https://www.pinterest.com/timemagazine"]}},{"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"item":{"@id":"https://time.com/collections/100-most-influential-people-2024/6964621/katsuhiko-hayashi-2/","name":"Katsuhiko Hayashi"}}]},{"@context":"https://schema.org","@type":"VideoObject","name":"See Everyone on the TIME100 2024 list","description":"","thumbnailUrl":"https://cdn.jwplayer.com/v2/media/73p9kgIN/poster.jpg?width=720","uploadDate":"2024-04-17T11:00:00.000Z","contentUrl":"https://cdn.jwplayer.com/manifests/73p9kgIN.m3u8","embedUrl":"https://time.com/collections/100-most-influential-people-2024/6964621/katsuhiko-hayashi-2/","duration":"PT1M59S","potentialAction":{"@type":"SeekToAction","target":"https://time.com/collections/100-most-influential-people-2024/6964621/katsuhiko-hayashi-2/?jw_start={seek_to_second_number}","startOffset-input":"required name=seek_to_second_number"}}] ```