Monday, September 10, 2007

Evolution by Natural Selection

The lesson for Monday September 10th covered chapter 22 "The Evidence for Evolution". Today's lesson went over the concept of evolution by natural selection. People often believed and were lead to believe that all life was made by the creator in perfection and was unchanging. There is evidence all around the earth such as the fossil record which gives evidence that the world is always changing. Charles Darwin was a naturalist in the 1800s who traveled on the Beagle to observe the world around him. He did not come up with the idea of evolution. Evolution had been understood by people before him like the Egyptians since evolution means change over time. Darwin came up with evolution by natural selection.

A portrait of Charles Darwin:
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Natural selection by definition is the differential reproduction of genotypes; caused by factors in the environment which leads to evolutionary change. This means that certain traits are selected in a species that are advantageous and help them to survive, depending on their environment, and are passed on to future offspring. Darwin's most famous supporting evidence is the finches in the Galapagos Islands. There he observed that there were different types of endemic birds with similar phenotypes. Later he found out that all the birds were finches. All the finches came from a common ancestor but they had adaptations which helped them to survive in the environment. All had different shaped beaks which were best for their survival. The variation in beaks within the same species enabled some to obtain food successfully in the different environments.

Adaptive radiation is where different species originate from a similar ancestor and they inherit different successful adaptations to fulfill their niches. A niche is the position of a species or population in the ecosystem. Organisms cannot choose the traits they want, they cannot adapt but have adaptations.

Lamarck was a naturalist who believed that organisms could adapt and change during their lifetime and pass those useful traits onto future offspring. Darwin and Lamarck were both observers of the world who had great ideas about how the world worked but evidence now shows that natural selection is more accurate and that organisms cannot choose their own genes and that genes are picked at random when an organism is created.

In conclusion, Darwin did not propose evolution but evolution by natural selection. He supported his idea with experiments like that with the finches from the Galapagos Islands. Natural Selection would fall under Evolution in the eight themes of biology.

I found these cartoons online. These show that organisms cannot adapt and choose traits they desire but it is a long process where organisms have adaptations.

This diagram shows the difference between LaMarck's theory and Darwin's using giraffes (click to see larger version):

To read more about Charles Darwin's Origin of Species or his journal and diary while on the Beagle go to this site:

1 comment:

KB Foglia said...

Wow! Great job, Saad! Talk about setting the bar high! Great summary, excellent use of graphics. I absolutely love those cartoons! I am going to incorporate them into my PPTs for next year. Thanks! And they make some great points to clarify misconceptions often held by students. Can you catch yourself making some of these same errors when you talk about evolution? Hmmm, maybe these should show up on an upcoming exam...wink, wink...