Evolution BSCS : Unit 4

A history of life on Earth Charles Darwin is the name most associated with evolution, but he did not publish his views on the subject until We need to understand the ideas of the time before we examine his radical new theories… 2 common ideas about life on Earth: Earth was less than 10,000 years old Fixed species – species do not change

The French Connection Buffon – French naturalist who, in the mid 1700’s examined fossils he believed to be more than a few thousand years old. Noted similarities between fossils and living creatures. Lamarck – French naturalist who, in the early 1800’s proposes to explain Buffon’s observations. Species are not permanent, life changes or evolves. Evolution explained as a process of adaptation. “Inheritance of acquired characteristics”

Inheritance of acquired characteristics

Great Scots! Hutton – Scottish geologist who proposed in the late 1700’s, that Earth was formed much the same way that we see changes occurring today. Gradual change that can be immense over time. Uniformitarianism is born. Lyell –Another Scot geologist who furthered Hutton’s ideas in the early 1800’s. Erosion and earthquakes are examples that are attributed as geologic processes that can account for the changes in Earth’s physical features.

Can’t stop the pop. Malthus – British demographer, whose ideas on population growth in the early 1800’s had a large impact on scientific thought and ideas to come. His observation that populations grow geometrically while resources do not, led to the explanation of disease and competition as components of man’s “struggle for existence”.

The Beagle sets sail In 1831, the HMS Beagle embarks on a ‘round-the- world voyage. The mission? To chart the South American coastline for the British Navy. Along for the ride was a 22 year old biologist by the name of Charles Darwin. He wanted a chance to study the plants and animals on the trip. Through specimens he collected, pictures he sketched, and journals he kept, Darwin’s ideas began to change. He left with many of the beliefs common in his time. By the time he returned to England, he had seen things that began to make him question…

What did he see? Many species of South America. These were similar to European species, but quite distinct at the same time. Even fossils he found were different from what he was used to. Some fossils were similar to living creatures, but much larger than anything still alive. This led to the idea that the living species were descendants of those in the fossil record. The Galapagos Islands. Young volcanic islands that had many similar species to the mainland, but were different, even from island to island. His idea was similar to that of Lamarck’s … that the species must have adapted to the new environment.

More observations While in South America, Darwin found marine fossils high in the mountainous regions, and even experienced an earthquake while in harbor where he noticed an underwater landmass had been heaved up above the water level, exposing it to the environment for the first time. He concluded that this could be along the lines of what Hutton and Lyell had explained in their theories.

5 years later… Upon returning home, Darwin had amassed a large collection of fossils, had volumes of journals, and had seen organisms that varied greatly from place to place. Due to the specimens he sent home while on his journey, he had gained quite a reputation back home as a respectable scientist. When he left, his ideas about life were on par with most others’. After his return, he had developed 2 new ideas based on his experience. The Earth was old. Species change.

Putting it all together So, if Darwin thought that species changed over the Earth’s long life, he had to come up with an explanation for how this occurred. If species change, it must be for a reason. What is the reason? Selective breeding of livestock and animals leads to a change, but that is not what happens in nature. Malthus’ ideas of competition strike a chord, and he proposes that this must be what drives the changes.

Darwin’s Idea He writes his ideas in 1844, but only tells a few close colleagues of his ideas. They encourage him to publish before someone else beats him to the same conclusions, but he sits on the writings until 1858, when another scientist by the name of Wallace has the same ideas. Darwin publishes his ideas a year later in Origin of Species. In it he outlines two main points: Descent with modification – based on evidence Natural Selection – the mechanism for evolution