Vertebrates & Invertebrates
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If you are an animal in the possession of a back bone or spinal column you are a vertebrate. They compromise many species of animals and fishes, reptiles and birds. If you do not have a backbone you are called an invertebrate. There are over 50,000 species of vertebrate. That sounds like a lot but there are far more invertebrates. Vertebrates are usually much larger than invertebrates. Vertebrates are smart, some of them are very smart, like humans. Most vertebrates have an advanced nervous system, muscles and skeleton.
Evolution is a theory that explains why animals and plants are so good at surviving in their environments. Evolution explains why species change over time. The theory of evolution was developed by Charles Darwin in 1859. Darwin believed that evolution occurs through natural selection. Animals and plants that are best able to survive also fit better into the ecosystem are far more likely to live.