Early Thoughts and Darwin’s Thoughts The Beginning of the theory of evolution

Early thoughts Before the idea of evolution, scientist believed that species had remained unchanged since their creation. This belief was rooted in religious belief and not backed by science.

Mid-18th century ideas The mid-18th century began booming biologist trying to classify organisms. Carolus Linnaeus came up with the binomial nomenclature (a 2 part naming system we still use today)

Mid-18th century ideas George-Louis Leclerc spent his life working on a 44 volume natural history series that described all known plants and animals Erasmus Darwin (Darwin’s grandfather) supported evolution with his writings on changes in animals during development, animal breeding by humans and the presence of vestigial structures (anatomical structures that appear to function in an ancestor but have long since lost most or all of their functions in descendants.

Late 18th/early 19th century ideas Baron Georges Cuvier- he used comparative anatomy to develop a system for classifying animals. He also founded the science of paleontology. He believed species stay unchanged since creation but as he studied fossils more, he saw changes in fossils between the different layers of sediment. This lead to the idea of catastrophism.

Late 18th/early 19th century ideas Jean-Baptiste de Lamarck proposed the idea of acquired characteristics, where an organisms environment can cause physical changes that are then passed on to offspring. Ex: A giraffe’s long neck James Hutton suggested the idea that the earth changes over slow erosion processes and not major catastrophic events. This helped support the idea that the earth was much older than originally believed. Thomas Malthus was an economist who studied growth and declines in populations. He proposed the size of the human population is only limited by the availability of resources. An idea Darwin applied to this theory later.

Darwin’s background He loved and studied nature from childhood. At 16, he was enrolled in Medical School, but did not take to the study of medicine. His father then enrolled him in The School of Divinity at Christ’s College at Cambridge. While there, he befriended John Henslow, a botanist, and Adam Sedgwick, one of the founders of modern geology. He gained many skills in collecting and identifying organisms and Henslow encouraged him to take a voyage on the HMS Beagle as their naturalist.

Darwin’s observations Darwin’s voyage on the HMS Beagle was only suppose to last 2 years, but turned into a 5 year trip, traveling all over the southern Hemisphere. During their stop in present day Argentina, Darwin uncovered fossils of Glyptodon and Mylodon and found fossils high up in the Andes Mountains. Glyptodon (the size of a small car) Mylodon- a giant ground sloth

Darwin’s observation Darwin also noticed through his travels, that although the species in the south were different there were some similarities between the animals of the northern and southern hemisphere. Rabbits and the Patagonian cavy The Greater Rhea and The Lesser Rhea

Darwin’s observations Most notable among Darwin’s observations are those he made while on the Galapagos Islands- a small group of volcanic islands off the coast of South America. The islands seemed to have their own type of tortoise, which varied from island to island. Tortoise with short necks seemed to inhabit the islands with plenty of rainfall and ground vegetation. But tortoise with long necks inhabited the dryer islands with tall cacti for food.

Darwin’s observations Darwin also did an intense study of the finches found on the Galapagos Islands. He concluded that based on where the finch lived (ie: on the ground or in a tree) and the diet (insects, nuts, berries) determined the size and shape of the finch’s beak.

Darwin’s observation As Darwin began looking around, he realized that humans have always been selecting for specific traits to benefit mankind (artificial selection) Examples of this is dog domestication and breeding, or higher yielding crops

Darwin’s conclusions Earth is very old. Events observed today must have also happened in the past. Organisms struggle for resources and mates. Some organisms are better competitors than others. Traits can be selected.

Darwin’s conclusion Darwin reflected on his observations and collected addition evidence. In 1858, with the help of Alfred Russel Wallace, the two proposed the idea of natural selection.