EVOLUTION

Jean Baptiste de Lamarck (1809) – He developed a theory of evolution. He related fossils to living animals based on similar appearance. He was the first to state that organisms change over time, and new types are modified descendents of older types.

Lamarck stated that acquired traits could be passed to offspring (The Theory of Acquired Inheritance)

This means that according to "All which has been acquired, laid down, or changed in the organization of individuals in the course of their life is conserved by generation and transmitted to the new individuals which proceed from those which have undergone those changes.” This means that according to Lamarck, acquired traits could be inherited by the next generation.

The Giraffe example: The giraffe’s long neck could be the result of generations of giraffes stretching to reach leaves in high branches over their lifetime. Parents slightly stretch their necks and therefore have offspring that inherit this modification acquired during their parents’ life.

If a giraffe stretched its neck for leaves, for example, a "nervous fluid" would flow into its neck and make it longer. Its offspring would inherit the longer neck, and continued stretching would make it longer still over several generations.

A new look at giraffe neck adaptation

The Long-Legged Bird Example: The long legs of wading birds arose when their ancestors responded to a need to feed on fish. As they waded in deeper water, they stretched their legs to try and keep their bodies dry. This trait would be passed to the next generation.

Example of webbed feet:

"The development of organs and their force of action are constantly in ratio to the employment of these organs." Lamarck stated that there could be changes in acquired traits through use or disuse.

Lamarck also proposed that organisms were driven from simple to increasingly more complex forms. (Darwin argued that increased complexity was the result of adaptation to local environments from one generation to the next.) He did not think species ever went extinct, they just changed into new forms.

Statue of

Charles Darwin (1809 – 1882) After college, a young Charles Darwin (22 yrs old), in 1831, set sail aboard the HMS Beagle as the ship’s naturalist. (The ship was chartered for a five-year mapping mission.) Darwin 1840

Darwin was required to collect specimens and carefully record his observations. Darwin was often left at various sea ports for months at a time, which enabled him to collect many fossils and observe thousands of specimens.

Darwin’s Voyage

Darwin read Principles of Geology by Charles Lyell, who stated that the geological structure of the Earth resulted from cycles of observable processes that operate continuously through time.

Extremely long periods of time. He estimated the Earth to Darwin also read about James Hutton’s work: In 1795, Hutton, a geologist, published a theory that the Earth is shaped by geologic forces that take place over Extremely long periods of time. He estimated the Earth to be millions of years old.

During Darwin’s journey, he witnessed a volcanic eruption, & an earthquake that lifted a portion of shoreline and noted that animal life in the water was displaced.

Darwin also observed fossil shells of marine organism in rock beds about 4,300 meters (14,100 ft) above sea level. Darwin concluded that if the Earth could change over time, then life could change as well. He also assumed that it would have taken many, many years.

The Galapagos Islands are a group of small islands near the equator, about 600 miles off the coast of South America. The observations and specimens Darwin collected were especially important to developing his theory.

white areas over islands are clouds

Darwin’s Finches: Darwin collected many specimens of finches from the Galapagos Islands and found that he had several similar but separate species.

Darwin had collected 13 different species, each with a different bill specialized for a particular food source.

Miller & Levine Biology

Since there were so many similarities, he believed this implied that the finches shared a common ancestor. He assumed the differences in the bills of offspring were adaptations to different environments. He also assumed that over many millions of years, many large differences could accumulate between species.

Darwin’s tortoises: Darwin found that the shapes of tortoise shells corresponded to different habitats.

The hood Island tortoise has a long neck and a shell that is curved and open around the neck and legs, allowing the tortoise to reach sparse vegetation. The Isabela Island tortoise has a dome-shaped shell & a shorter neck. Vegetation on this Island is more abundant and closer to the ground. Pinta Island tortoises have an intermediate shell between these two forms.

Another important idea that aided Darwin’s conclusions about the change in organisms was proposed by Thomas Malthus in 1798. He stated that the human population could double & redouble, except for the presence of war, disease, or limited food supplies.

Darwin’s conclusions: 1) Darwin reasoned that all organisms have environmental limits to their growth which decrease their rate of reproduction or increase their rate of death. 2) Organisms compete for limited resources. 3) Certain traits are beneficial to an organism’s survival, as well as greater reproductive success. If the trait increases the reproductive success, & is inherited, it is passed to many offspring.

4) Organisms adapt to their environment . (Adaptations occur as their proportion of genes for favorable traits increases. – Darwin did not know about genes) 5) The resulting change in genetic makeup is evolution. The genetic contribution to the next generation termed fitness. 6) An individual with a high fitness is well- adapted to its environment and reproduces more successfully than an individual with low fitness. These are not Darwin’s – But related to Evolution:

Natural Selection -“Survival of the fittest.” Individuals best suited to their environment survive and reproduce the most successfully, and pass their favorable traits to offspring. While those with more poorly -suited traits die, or leave fewer offspring.

Species change over long periods of time. Natural selection causes the changes in species. New species arise, while others Species alive today descended, with modifications from species that lived in the past. All organisms on Earth are united in a single tree of life by common descent.

Artificial Selection and Natural Selection: Breeding organisms with specific traits in order to produce offspring with identical traits is called “Artificial selection.” Darwin used the term “Natural selection” to describe nature’s forces Selecting which traits are favorable and which organisms are better fit to survive.

Natural Selection, the key evolutionary mechanism Darwin identified, is really four key processes genetic variation (difference in genomes among organisms in a given population) overproduction of offspring struggle for existence (competition for food, mating resources etc.) differential survival and reproduction (higher fitness, & better adaptation leads to more offspring).

Natural Selection (Modern Biology pg 300)

Overproduction of Offspring & Struggle for Existence Genetic Variation

Differential Survival Reproduction

Natural Selection and peppered moths: As pollution darkens the trees which moth is favored to survive?

Darwin was asked by the naturalist Alfred Wallace, in 1856 (22 years after Darwin returned to England on the Beagle) to review his paper on “Natural Selection” as a mechanism for Evolution. Darwin decided to publish his own work on evolution. Both papers were presented to the Linnaean Society of London in 1858.

Darwin wrote his now famous book, On the Origin of Species by Means of Natural Selection, more commonly known as The Origin of Species.

What causes changes in a population of organisms? Darwin did not know how heredity worked. Therefore he did not know the source of the variation that was central to his theory, or how these traits were passed to offspring.

Two main sources of genetic variation: 1) Mutations - Mutations do not always affect an organism’s phenotype, but some may enhance an organism’s ability to survive and reproduce. 2) Sexual reproduction - The Genetic shuffling that results from sexual reproduction causes variations in a population. Genes mutate from one form to another. New alleles are introduced into the population, and allele frequencies change. -------This can lead to evolution.