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400
Ancient Greek Philosophers
Around 400BCE, Ancient Greek philosophers like Plato and Aristotle believed all life existed in a perfect and unchanged world. All life has remained unchanged since creation. They also belived that there was a defined hierarchy of life, with humans being the perfect form at the top, and ruling over all other organisms. -
Period: 400 to
Dominant Idea of Perfect, Unchanging Life
For about 2000 years, the idea that life was perfect and unchanging and humans ruled over all other organisms was predominate in western culture. Church doctrines supported this idea and proposed that Earth was 6000 years old (based on geneologies from the Bible). -
Georges-Louis Leclerc, Comte de Buffon (1707-1788)
Buffon was a French naturalist, and one of the first people to challenge the idea publicly that life forms are unchanging. His book, Histoire Naturelle, noted the anatomical similarities between apes and humans, speculated that they shared a common ancestor and also suggested that the Earth was older than 6000 years. His ideas were revolutionary at the time. -
Georges Cuvier (1769-1832)
Cuvier (the Father of Paleontology), also contributed his ideas on life. He studied fossils in stratum. The deeper the fossils were, the more dissimilar to life today they were. Also, fossils seemed to appear and disappear, proving species could become extinct. To explain his observations and keep in line with the accepted age of the Earth (6000 years), he created his catastrophism theory. Violent events called revolutions had caused many species to go extinct at various times in Earth's history -
Period: to
The Life of Darwin (1809-1882)
Over Darwin's lifetime, he observed a great variety of things and ultimately formulated the Theory of Evolution by Means of Natural Selection that is widely accepted today. -
Charles Lyell (1797-1875)
Scottish geologist Lyell rejected Cuvier's catastrophism theory. He stated that geologic processes happened no faster or slower in the past than they happen today (floods of the past were no more powerful than floods today). He reasoned that if geologic processes happen slowly, the Earth has to be more than 6000 years old to allow for the vast changes seen in organisms. This also gave rise to the question, if Earth is slowly changing, could slow and subtle changes also happen in populations? -
Jean-Baptiste Lamarck (1744-1829)
Lamarck's book, Philosophie Zoologique, outlined his ideas about changes in species. He compared fossils and animals and found a "line of descent", species increased in complexity over time until they achieved a level of perfection. He formualted a Hypothesis of Inheritance of Acquired Characteristics. Lamarck believed that traits accumulated through an organism's life (like large muscles), were passed on to offspring and helped them survive. -
Darwin Leaves on the HMS Beagle
Darwin left England on a British survey ship that primarily explored the Pacific coast of South America, and the Galapagos Islands. He observed that the organsisms here were distinctly different from the ones in Europe and found fossils that looked very similar to their living counterparts. However, it was on the Galapagos that he found the slight differences between finches (beak shape) and tortoises (shell shape) on different islands, which became his main evidence for evolution. -
Darwin Arrives Back in England
Upon arriving back in England, Darwin examined the evidence he had accumulated on his voyage. This led to various questions. Why did fossils and living organisms look so similar? Why did the species on the Galapagos look so similar to those on South America? What caused the slight differences between finches and tortoises on the different islands? The answers to these questions led to his theory of evolution. -
Alfred Russel Wallace (1823-1913)
Darwin was not the only one to come to conclusions about natural selection and evolution. Another British naturalist, Wallace, conducted research in the Amazon River basin and Malay Archipelago. He sent letters to Darwin outlining his ideas on population change, and they were very similar to Darwin's own ideas. These were made public in a presentation in 1858. -
Thomas Malthus (1766-1834)
An essay, Essay on the Principles of Population, by economist Mathus gave Darwin and Wallace the missing piece they needed to complete their theory. He proposed that populations produced far more offspring than their environments could support, and were eventually reduced down to a sustainable level through starvation or disease. This inspired Darwin and Wallace as to "how" populations changed. -
On the Origin of Species by Means of Natural Selection
Darwin's famous and revolutionary book was published in 1859. The book proposed two major ideas. First, present forms of life have arisen through descent and modification from an ancestral species. Secondly, the mechanism for modification is natural selection working for long periods of time. Due to limited resources and competition, those organisms best adapted are more likely to survive and reproduce. Over time, these traits become more and more frequent, and the population changes. -
Molecular Biologists (Mid-1900's)
Loose ends in Darwin's theory were tied up by breakthroughs in molecular biology in the mid-1900's. An understanding of how traits were passed on through gametic cells, and not through somatic cells, proved Darwin's theory. Other discoveries like that of DNA and RNA also furthered evolutionary theory.
