Our planet is filled with a dazzling variety of creatures that collide with the ugly to reproduce. Cats do it. Dogs do it. The birds and the bees definitely do. But what were the first animals to have sex?
Animals have been reproducing sexually since they evolved, so the first animals to have sex were the first animals to exist. Researchers are still looking for direct animal evidence, but they are likely to emerge within the last 800 million yearslived in the ocean and looked like the sponges.
According to Exploring our Fluid Earth website hosted by the University of Hawaii.
But while ancient sponges may have been among the first animals to reproduce sexually, the act itself passed them by long ago. That’s because life forms were having sex before animals came on the scene.
“The first animals to have sex had sex before they were animals.” John Logsdonan associate professor of biology at the University of Iowa, told Live Science.
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Logsdon tracks sexual reproduction by looking for the presence of Meiosisa form of cell division that creates reproductive cells in eukaryotes – organisms with a nucleus in their cells, such as animals, plants and fungi.
“It’s pretty clear that all eukaryotes either had the ability to do meiosis or have the ability to do meiosis,” Logsdon said. “The logical conclusion there is that a common ancestor of all of us did.”
So when did the first eukaryotes evolve? According to Logsdon, the answer is about 2 billion years ago, when simple bacteria would have participated in some kind of genetic exchange.
But sex between sponges and sea bacteria is quite different from intercourse, or copulation, in which humans and many other animals engage, which relies on a more intimate internal fertilization. For the first evidence of this, scientists look to ancient fish fossils.
“The earliest evidence of intimate sexual reproduction using copulation is from placoderm fishes of the Devonian period. [419.2 million to 358.9 million years ago]HOW Microbrachius dicki“, John Longa professor of paleontology at Flinders University in Australia and author of “The Dawn of Work: The Prehistoric Origins of Sex” (The University of Chicago Press, 2012), told Live Science in an email.
Fossils reveal this M. dicki males had paired claspers to inseminate females internally, while females had reciprocal genital plates. Long and his team found that the male and female fish would have stood next to each other during mating with their arm-like limbs connected, so the first sexual act would have it looked like square dancing.
“We have placoderms to thank for both the joy of sex and the work of childbirth,” Long wrote in his book.The Secret History of Sharks” (Ballantine Books, 2024).
Sexual reproduction has many benefits. First, offspring receive genes from both parents, unlike asexual reproduction, in which offspring receive genes from only one parent. This mix of genes enables animals to adapt better to changes in their environment.
“Sexual reproduction means that the genetic makeup of the offspring is more diverse than asexual creatures that simply clone themselves (like jellyfish), so it is much less likely that the entire population of the species will be vulnerable to extinction from disease,” Long said. . “This greater variability in the gene pool increases survival not only [against] pathogens, but also for environmental changes, e.g. climate change, or even better tolerance to chemical toxicity, if we say that volcanic eruptions change the chemical composition of seawater.”