In a previous post, you learned that evolution is a theory, and a theory is something that all the scientific evidence supports. In another post, you learned about the theory of evolution. But, how did the theory of evolution come about? What was the evolution of evolutionary thought?
In order for the theory of evolution to be developed, some old ideas needed to change. In this post, we will explore the first idea, having to do with the relationship between humans & other life.
The OLD IDEA was: Humans were separate from other forms of life.
The NEW IDEA was: Humans were related to other forms of life.
A long time ago in Europe, people wondered how humans and the other life on Earth were related. Aristotle came up with the idea of a Great Chain of Being, which meant that everything on earth could be ordered from simple to complex. God was on top, then angels, and then humans, then lower down were animals and plants, and at the bottom were minerals, meaning rocks. People accepted this idea, believing that humans were separate from animals and other forms of life.
But starting in the 17th Century, some scientists challenged the Great Chain of Being. They realized that some organisms seemed to have similarities with other organisms, and so maybe life could be grouped in different ways.
A man named John Ray found out that some animals could mate with each other and reproduce, and others couldn’t do that. So, he called the groups that could do this, “species.” (So, a species is just a group of organisms that can mate and produce fertile offspring.) Ray also figured out that some species have a lot in common with other species, and he grouped these into a higher-level group called a “genus.” His terms genus and species are still used today, for example, we are Homo sapiens. Homo is the genus, and sapiens is the species.
Then, in the 1700s, Carl Linnaeus took Ray’s classification system and added the categories of “class” and “order.” Linnaeus looked at the similarities and differences among organisms, and he grouped them by these physical characteristics. But he even did this with humans, which went against the Great Chain of Being–people thought that humans were special and separate from animals. While it was very controversial during his time, his system became the basis for our current system of classification, called taxonomy.
In summary, people used to think that life was a hierarchy involving a Great Chain of Being, and that humans were separate from the other forms of life. Thanks to John Ray and Carl Linnaeus, scientists realized that all forms of life could be grouped in a different way, and humans were actually related to other forms of life. In the next blog post, we’ll explore the second idea that needed to change in order for the theory of evolution to be developed.
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Thanks for reading!