Our world is full of an amazing variety of creatures that go out of their way to reproduce. Cats do that. Dogs do that. Indeed the birds and the bees do. But what were the first animals to have sex?
Animals have been reproducing since they evolved, so the first animals to have sex were the first animals to exist. Researchers are still looking for direct evidence of the first animals, but they may have appeared during the last 800 million yearsit lived in the sea and looked like sponges.
Sponges in our oceans today reproduce sexually by releasing sperm and egg cells into the water, which combine to form new sponge worms, according to Knowing Our World and Water a website operated by the University of Hawaii.
But while ancient sponges may have been among the first animals to reproduce sexually, the act itself predates them. That’s because life forms had sex before animals.
“The first animals that had sex were already having sex before they were animals,” John Logsdonassistant professor of biology at the University of Iowa, told Live Science.
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Logsdon follows the production of sex by looking for the presence of meiosistype of cell division that produces reproductive cells in eukaryotes – organisms that have a nucleus in their cells, such as animals, plants and fungi.
“It is clear that all eukaryotes have the ability to undergo meiosis or have the ability to undergo meiosis,” Logsdon said. “The logical assumption there is that a common ancestor of all of us did.”
So when did the first eukaryotes appear? According to Logsdon, the answer is about 2 billion years ago, when simple bacteria he would have participated in some kind of genetic exchange.
But sexual relations among marine sponges and bacteria are very different from the sexual relations that humans and many other animals engage in, which rely on intimate internal fertilization. For the first evidence of that, scientists look at fossils of fish.
“The earliest evidence of sexual reproduction by mating comes from a placoderm fish of the Devonian period. [419.2 million to 358.9 million years ago]like Microbrachius dicki,” John Longprofessor of paleontology at Flinders University, Australia and author of “The Dawn of the Deed: The Prehistoric Origins of Sex“(University of Chicago Press, 2012), told Live Science via email.
Archeology reveals that M. dicki men had claspers packed internalizing females, while females had alternating genital plates. Long and his team discovered that the male and female fish would have been side-to-side during contact with their hand-like arms linked, so the first act of sex would be there. it looked like a square dance.
“We have placoderms to thank for both sexual pleasure and reproductive function,” Long wrote in his book, “The Secret History of Sharks(Ballantine Books, 2024).
Sexual reproduction has many advantages. One reason is that children receive genes from both parents, as opposed to abnormal reproduction, in which children receive genes from only one parent. This combination of genes enables animals to adapt well to changes in their environment.
“Sexual reproduction means that the genes of the offspring are more diverse than those of only sexually mixed organisms (such as jellyfish), so there is a very small chance that entire populations of these species are at risk of being wiped out by disease.” ,” Long said. . “This great diversity in genetics improves life and not only [against] microbes, but also for environmental changes, for example, climate change, or better tolerance of chemical toxins when volcanic eruptions change the chemical composition of sea water.”
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