Why do giraffes have long necks? Answers to 25 animal evolution questions
About a billion years after the Earth formed, the first signs of life emerged. These were just single-celled microbes, but through billions of years of evolution, scientists think that one of these organisms became a common ancestor to all life, including animals.
Evolution has shaped life ever since it first emerged, progressing for more than 2 billion years before the first animals evolved from their primal ancestors. Since then, the animal kingdom has adapted to fill niches nearly everywhere on the planet, from the sea to subterranean tunnels.
Evolution encompasses the changes species undergo over long time periods. It describes how a species’ gene pool can gradually change over time, thanks to random DNA mutations or sexual reproduction introducing new genetic combinations. Traits can emerge that help individuals survive to reproduce and pass on their genes to future generations.
Nineteenth-century naturalist Charles Darwin used natural selection, or “survival of the fittest,” to describe a major aspect of evolution. According to this theory, individuals with traits better suited to the environment are more likely to survive to pass on their traits to offspring. For example, if there are a few beetles with superior camouflage in a group with other beetles that stand out, the camouflaging beetles will have a higher chance of surviving and reproducing. Over many generations, the species will adapt to their surroundings as more beetles with that camouflage trait make up the population.
Evolution is driven by interactions between genetics and nature, and the Earth’s rock layers preserve a record of this process. By studying fossilized remains, scientists can learn about how modern animals evolved.
But how these animals came to live where they live, look the way they look, and do the things they do is rarely obvious. By consulting scientific research and news articles, Stacker compiled a list of 25 animal evolution questions and answers to explain some of those mysteries, from why giraffes have such long necks to how ants can carry 50 times their body weight. Read on to find out how evolution has led to the diversity of animals on the planet.
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What was the first animal to evolve?
For biologists to call it an animal, an organism needs to be able to eat and must consist of multiple nucleus-containing cells that have specific functions. Sponges, filter-feeding organisms often anchored to rocks or the sea floor, were the first animals to evolve around 600 million years ago. Scientists theorize that sponges arose from colonies of single-celled organisms that eventually evolved into a multicellular animal, with groups of cells evolving into specialized cell types.
What’s the simplest known animal?
Trichoplax adhaerens is the simplest animal known, just three cells thick, lacking nerves, organs, and even a mouth. Trichoplax, an evolutionarily old species, make up for their boring physique with their interesting genes. Trichoplax have the same genes of more complicated animals, including ones that help create nerve cells. This suggests that early on in animal kingdom history, creatures like Trichoplax already possessed genes needed for more complicated forms, and later animals merely evolved different uses for those genes.
Why are there gaps in the fossil record?
The preserved remains and impressions of life forms found in ancient rocks, some dating back to the times of the early microbes, is known as the fossil record. While it contains a wealth of information, from evidence of 600 million-year-old sponges to preserved teenage T. rex bones, there are some apparent gaps in our planet’s evolutionary history.
For example, for a while scientists lacked any fossil evidence indicating how vertebrates transitioned from the ocean and evolved limbs necessary for life on land until a few years ago, when they finally found the “missing” fossils. Other gaps may exist simply because the conditions necessary to fossilize didn’t happen—less than a 10th of 1% of all species that have lived on Earth have become fossils.
Are immortal jellyfish really immortal?
No, they're not truly immortal jellyfish, but Turritopsis dohrnii, as it's known among scientists, can reverse age: If it's in the adult stage of the life cycle, it can revert back to its juvenile stage. This species is often likened to Benjamin Button. Scientists have yet to fully understand how these jellyfish developed their abilities, but they're learning that other jellyfish species might have evolved similar propensities.
Where did tardigrades come from?
Tardigrades, more commonly known as water bears or moss piglets, have a reputation for being nearly indestructible. These microscopic creatures can survive extremely dry conditions, withstand temperatures from near absolute zero to 300 °F, and exposure to outer space. But how these animals came to be is still a mystery. From analyzing the genomes and body structures of different tardigrade species, scientists have theorized that tardigrades’ closest relatives are either nematodes or arthropods.
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Why are ants so strong?
Ants are commonly spotted carrying bits of food and even pebbles back to their colonies, lifting 50 times their body weight. Ants, and other insects, are so strong because of their strength-to-weight ratio: Compared to a larger animal, less mass means that ant muscles don't need to work as hard to support the body, leaving more power available for heavy lifting. Insects can thank Earth's atmosphere for their body composition, as bugs used to be larger, but shrank over time when Earth's oxygen levels decreased.
Why do peacocks have such showy feathers?
Peacocks evolved their display because of sexual selection, according to Charles Darwin. Peahens were selective with their mates and would only choose the most impressive peacocks to pass on their genes to the next generation. This meant that the next generation could have yet more flashy birds. The theory of sexual selection asserts that peacocks and other male birds evolved their feathery displays and elaborate mating rituals because their female ancestors chose the birds with the most impressive features.
Why do turtles have shells?
From studying turtle embryos, scientists know that a turtle's shell originates from its ribs and vertebrae. This form originated over 250 million years ago, by which time modern turtle ancestors that lived on land had evolved half a shell, expanding from the lower ribs and covering their underside. Scientists debate why the shell evolved, but one idea is that the bottom half evolved to help early turtles dig into muddy river banks, and the rest of the shell evolved as a protective mechanism as slow-moving turtles transitioned to aquatic habitats.
How can a 3.5-ounce bird make the world's longest migration?
Arctic terns are no bigger than a quarter of a pound but complete the longest migration on Earth each year, flying about 60,000 miles from Greenland to Antarctica and back. The birds' lightweight physique allows them to glide with the wind, taking a circuitous route on their flight, and helps them preserve energy. Scientists still aren’t sure why birds evolved these arduous migrations, although a popular theory holds that birds’ annual searches for food or breeding grounds slowly expanded over time.
Why are there so many marsupials in Australia?
While scientists aren't sure why marsupials have been so successful in Australia, they do know how these mammals arrived. Marsupials are mammals but give birth to undeveloped young that finish developing in the mother’s pouch. They began evolving around 160 million years ago, and the oldest marsupial fossils are from North America. The fossil record shows that over tens of millions of years, as marsupials evolved, they spread to South America—where they still thrive—and then spread through Antarctica, which was warm, lush, and close to South America 40 to 35 million years ago. From there, Australia wasn't too far away.
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