Earth's first animals barely evolved until sex changed everything

Date: June 10, 2026 Source: University of Cambridge Summary: Earth’s earliest animals may have held evolution back because they reproduced asexually, creating low-competition communities that changed very little over time. When environmental pressures pushed them toward sexual reproduction, biodiversity exploded and evolution accelerated dramatically. Share: Facebook Twitter Pinterest LinkedIN Email FULL STORY Artist's impression of an Edicaran animal community. Credit: Hugo Salais A new study suggests that the earliest animals on Earth may have unintentionally slowed the rise of biodiversity. According to researchers from the University of Cambridge, the way these ancient organisms reproduced limited competition and kept evolution moving at a remarkably slow pace for millions of years. The findings, published in Nature Ecology and Evolution, offer a possible solution to a long-standing paleontological mystery. Although animals first appeared during the Ediacaran period, their diversity remained relatively limited for a surprisingly long time before a later burst of evolutionary innovation dramatically expanded life on Earth. Life's Early Experiment After billions of years dominated , the Ediacaran period, which lasted from about 635 million to 539 million years ago, saw the emergence of the first animals. Some of these creatures, including Fractofusus, reached heights of up to two meters, although most were much smaller. These early animals looked very different from anything alive today. Many resembled ferns more than modern animals and appear to have lacked mouths, organs, and the ability to move. Scientists believe they absorbed nutrients directly from the surrounding seawater. Like many other Ediacaran organisms, they vanished from the fossil record at the start of the Cambrian period roughly 540 million years ago. Their disappearance has made it difficult for researchers to determine whether they are related to any animals living today. Previous studies showed that many of these organisms reproduced asexually. They spread , or runners, much like modern strawberry plants. In the nutrient-rich oceans of the Ediacaran, this strategy worked extremely well. "Life was pretty nice during the Ediacaran, so the need for sex was rather limited," said lead author Dr. Emily Mitchell from Cambridge's Department of Zoology. "There was relatively little competition, so there was no real pressure to change anything." Fossils, AI, and Ancient Ecosystems To investigate why evolution appeared to slow during this period, Mitchell and co-author Professor Andrea Manica studied fossils from Mistaken Point in Newfoundland, one of the world's most important Ediacaran fossil sites. The researchers combined laser scanning, spatial analysis, and artificial intelligence to examine how these ancient communities were organized and how they may have interacted.