16-1 Darwin’s Voyage of Discovery

Charles Darwin:

• England

• traveled on the HMS Beagle as the naturalist

  • 5 year trip around the world — spent time in the Galapagos islands

  • collected specimens at each stop

evolution - change in living things over time

1. Darwin developed a theory of biological evolution that offered a scientific explanation for the unity and diversity of life by proposing how modern organisms evolved through descent from common ancestors

2. Darwin’s work revealed that the living world changes continuously

3. The evolutionary theory helps us understand and respond to important events such as the emergence of drug-resistant bacteria and new strains of influenza (flu)

Darwin observed 3 patterns of biodiversity on his voyage:

1. Species vary globally — different, yet ecologically similar species inhabited separated, but ecologically similar, habitats around the globe

2. Species vary locally — different, yet related species often occupied different habitats within a local area

3. Species vary over time — the fossil record included many extinct animals that were similar to, yet different from, living species

fossils - the preserved remains or traces of ancient organisms

The Journey Home:

1. Darwin observed that the characteristics of many animals and plants varied noticeably among the Galapagos Islands

2. After returning back to England, Darwin wondered if the birds he had collected all belonged to the same species at some time — proving that they had evolved, contradictory to the popular beliefs at the time

16-2 Ideas That Shaped Darwin’s Thinking

James Hutton and Charles Lyell — concluded that Earth is extremely old and that the processes that changed Earth in the past are the same processes that operate in the present

• Hutton proposed that layers of rock form very slowly and others are pushed up from the sea floor to form mountains

• Lyell’s principles of geology: the same process that changed the Earth in the past still operate in the present

  • ex. volcanoes, erosion

Darwin was influenced by Hutton and Lyell’s work

• he reasoned, if the Earth can change over time (earthquakes, volcanoes) maybe life can change too

Lamarck’s Evolution Hypothesis:

• Jean-Baptiste Lamarck observed that life changes and species descend from other species

• Lamarck had two ideas:

  • Organisms can alter their bodies by “use and disuse”

    • Use: use a structure and it will change

    • Disuse: structures not used will disappear

  • Acquired characteristics can be inherited

    • If you increase your muscle mass, your children will inherit your big muscles

  → Although, Lamarck’s ideas were incorrect

  • He was one of the first people to realize that organisms are adapted to their environments and to propose a theory of evolution

Thomas Mathus was an economist, he published a book which stated that babies were being born faster than people were dying

• he reasoned that if the human population continued to grow unchecked, sooner or later, food and living space would run out

• Darwin thought this applied to plants and other animals even more because humans usually only have one offspring at a time

Darwin observed that individual organisms differed from one another and that variation could be inherited

• farmers and breeders used this

artificial selection - selecting the best organisms to breed and pass on their trait

• nature provides the inherited variations, and humans select hose variants they find useful

• inherited variations could provide raw material for a natural mechanism that could drive evolution

16-3 Darwin Presents His Case

Darwin realized that organisms compete for resources — struggle for existence

He hypothesized that individuals with certain types of inheritable variation are better suited, or adapted, to life in their environment than others. He noted that organisms better suited to their environment survived to reproduce and pass on their genes

• ex. run faster, hide from predators

adaptations - any heritable characteristic that increases an organism’s ability to survive and reproduce in its environment

fitness - the ability of an animal to survive and reproduce in its specific environment

survival of the fittest - more than just staying alive, it means reproducing and passing adaptations on to the next generation

natural selection - the process by which organisms in nature with variations most suited to their local environment survive and leave more offspring

• in both artificial and natural selection, only certain individuals produce offspring, but in natural selection it is the environment, not a farmer or breeder, that influences fitness

• natural selection occurs in any situation in which more individuals are born than can survive

  • natural heritable variation affects the ability to survive and reproduce, and fitness varies among individuals

principle of common descent - all species, living and extinct, are united by descent from ancient common, and exhibit diversity due to natural selection and adaptation

16-4 Evidence of Evolution

A great deal of evolution remains to be learned, however, every scientific test, to date, has supported Darwin’s basic ideas

biogeography - the study of where organisms live now and where they and their ancestor lived in the past

• patterns in the distribution of living and fossil species, combined with information from geology, tell us how modern organisms evolved from their ancestors

two potential difficulties for Darwin’s theory involved the age of Earth and gaps in fossil record

• radioactive dating indicates that Earth is about 4.5 bil years old — plenty of time for evolution by natural selection to take place

• recently discovered fossils form sequences that trace the evolution from extinct common ancestors

homologous structures - similar structures that are shared by related species and have been inherited from a common ancestor

analogous structures - body parts of organisms that share common functions but not common structure and development

ex. wing of a bee and wing of a bird

vestigial structures - inherited from ancestors but have lost much of their original size and function

ex. hipbones of the bottlenose dolphin

• similar patterns of embryological development provide further evidence that organisms have descended from a common ancestor

• at the molecular level, similarities in the genetic code of all organisms, along with homologous molecules, provide evidence of common descent