Charles Darwin How one man’s observations and ideas helped to change the world

Standard: Explain that physical characteristics of organisms have changed over successive generations.

The voyage of the Beagle After two false starts, the Beagle set sail on her voyage on 27 th December 1831, with Charles Darwin aboard. The voyage lasted 5 years. The ship sailed to South America to carry out surveying work, and everywhere it went Darwin took detailed notes of what he saw and collected many specimens. Galapagos

Charles Darwin arrived in the Galapagos, a group of volcanic islands off the coast of Ecuador, South America on 15 th September The observations Darwin made during his visit were to be influential in the formation of his scientific theories. The Galapagos Islands

Variety is the spice of life Darwin was amazed at the wide variety of plants and animals he found during his voyage to the Galapagos Islands. The images below show some of the vertebrates that Darwin saw. Galapagos marine iguana Vermillion flycatcher Galapagos hawk perched on Galapagos giant tortoise

Darwin - the collector Darwin collected numerous specimens of plants and animals and kept detailed records of where and when he had found them. Many of the species he collected and classified were new to science at the time. Lots of Darwin’s specimens are still preserved in collections in universities and museums. Large ground-finch - Charles Darwin’s specimen

Darwin observed that each island had its own unique mixture of plants and animals. These were often adapted to survive in the different conditions found on each island. San Cristobal mockingbird – only found on San Cristóbal Daisy tree Scalesia divisa – only found on San Cristóbal Medium tree-finch – only found on Floreana

Darwin’s finches Darwin made detailed studies of one group of birds, the finches, because of their strong similarities and subtle differences. He noticed that the different finch species varied in size, beak size and shape, and behaviour. He thought that these differences could be best explained if the finches had gradually become adapted to suit the conditions on the island they inhabited. He presumed therefore that all 13 species of finch found on the islands must be closely related. He also deduced that the individuals with the best set of adaptations for each island’s habitat would be most likely to survive and breed.

Darwin’s finches

On the Origin of Species Darwin completed his voyage on the Beagle in For over 20 years Darwin continued to do experiments and collect data based on his ideas about the importance of adaptation and survival. In June 1858 he received a letter from Alfred Russel Wallace, another naturalist and explorer who was collecting specimens in Indonesia. Wallace shared similar ideas to Darwin about how living things could adapt and evolve. In November 1859, Darwin published his famous book ‘On the Origin of Species by Means of Natural Selection’ in which he described his evidence for evolution - much of which was first collected during the voyage of the Beagle.

Charles Darwin developed his theory of evolution by natural selection using four important observations which led him to two deductions. Observations: 1. All organisms produce more offspring than survive to adulthood 2. Populations remain more or less constant in numbers 3. Members of the same species show variation in characteristics 4. Some characteristics are inherited and so are passed on to the next generation Deductions: A. All organisms are involved in a struggle for survival and only the best adapted survive B. Organisms that survive are more likely to reproduce, and therefore pass on their useful adaptations to their offspring Introduction

1. All organisms produce more offspring than survive to adulthood One of Darwin’s first observations was that all living things are capable of producing more offspring than are needed to replace their parents. For example a female rabbit can produce up to seven kittens in a litter, but they don’t all survive to become adults. Observations

2. Populations remain more or less constant in numbers Darwin’s second observation was that the numbers of many different species of animals and plants tend to stay fairly constant over long periods of time. For example, herds of many animals live on the plains of Africa, wildebeest, zebra, gazelles etc. Each year many of the females give birth to young, but the overall population sizes of these species stay the same. There are a number of factors which keep the population numbers stable, including competition for food, predation and disease Observations

3. Members of the same species show variation in characteristics Darwin’s third observation was that all living things vary slightly in color, shape, size or behaviour. Below are three different colorings and skin patterns found in the giraffe. West African giraffeReticulated giraffeThornicroft’s giraffe Observations

4. Some characteristics are inherited and so passed on to the next generation Darwin’s fourth observation was that many features are passed on from parent to offspring. Some inherited characteristics are quite easy to see in humans: Eye color Hair color Some are not so easy to see: Blood group Observations

From his four observations Darwin was able to deduce two main conclusions. A. All organisms are involved in a struggle for survival. B. Some individuals are better adapted to their environment than others. Polar bears fightingPygmy seahorse camouflaged against fan coral Conclusions

Survival of the fittest The individuals that are best adapted to their environment are most likely to survive and have the chance to reproduce, therefore passing on their useful adaptations to the next generation. Those individuals that are the least well adapted do not survive long enough to breed. These ideas formed the basis of Darwin’s theory of evolution by natural selection. Male African lion Silverback mountain gorilla

Natural Selection OverproductionVariation Adaptation Inherited Traits

Evolution by natural selection Darwin concluded that natural selection could explain how organisms gradually change and evolve into new species. At the time of publishing Darwin found it difficult to get his theory accepted, as it was difficult to prove. Other scientists at the time wanted Darwin to provide an explanation to how individuals passed on their characteristics to their offspring. Since Darwin’s time advances in our understanding of genetics have provided evidence to support and extend Darwin’s theory.