French scientist, Lamarck, had an idea on evolution. For example, if a giraffes stretch its neck to reach high leaves it would eventually get longer.However he could not explain how this long neck could've been passed on.
Charles Darwin collected many specimens from the Galapagos. He noticed variation within species and develpoped the idea of Natural selection. He noticed that some birds had thin beaks good for picking insects from tree cracks and another had thick beaks which could crack nuts. They had all adapted to suit their enviroment.
He still could not explain how they were passes on but nowadays we know a lot about DNA so we can explain this.
There was a lot of religous beliefs that did not like Darwins idea so his work often got rejected. Other problems were the incomplete fossil recors and natural selection taking a long time( in the 1800's scientists only thought the earth was a few 1000 years old).
Earth is 4 billion years old
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