Change Over Time Who was Charles Darwin 1831

Change Over Time

Who was Charles Darwin? • 1831 • HMS Beagle set sail from England on a 5 year trip of discovery…. . • Darwin’s job was to learn as much as possible about the living things he saw on the voyage. • He saw many plants and animals he had never seen before • His discoveries led him to develop a scientific theory of evolution by natural selection.

Species: • Scientists estimate that there are 1. 7 million species of organisms on Earth. • Species – a group of similar organisms that can mate with each other and produce fertile offspring.

Galapagos Island • Here Darwin observed many unusual life forms • Giant Tortoise • Lizards • Seals

Similarities and Differences • Darwin noticed that some animals found on the Galapagos Island were similar to the animals found on the mainland (South America)

How did these creatures get here? • Darwin inferred that a small number of different plant and animal species had come to the Galapagos from the mainland. • Blown out to sea during a storm • Floated on a drifting log • Over time (millions of years), their offspring changed into what they are today….

Adaptations: • Birds – Finches • Differences depending on which island they came from • Size and shape of beaks • Eat insects: beaks were sharp, needlelike • Eat seeds: beaks had strong, wide beaks • Adaptation – a genetic trait that helps an organisms survive and reproduce

Theory of Evolution • Darwin spent 20 years studying his findings • Darwin reasoned that plants and animals that arrived on one of the Galapagos Islands faced conditions that were different from those on the mainland. • Perhaps species gradually changed over many generations and became better adapted to the new environment…… • Evolution – the change in species over time

Selective Breeding: • Evidence to support his theory of evolution

Natural Selection • Natural selection – the process by which individuals that are better adapted to their environment are more likely to survive and reproduce than other members of the same species. • Affecting factors: – Overproduction – Competition – Variation

Overproduction: • Most species often produce more offspring than can possibly survive • Why? What is passed on to the next generation?

Competition: • Food and other resources are limited • Members of species must compete with each other to survive. • Can lead to starvation and being prey for predators • Will the weak be able to pass on their DNA?

Variation: • Members of a species differ from one another in many of their traits • Any difference between individuals of the same species is called a variation. – Example: baby turtles swimming faster than their siblings…. . WHY? • Some variations can make an individual better adapted for survival.

Natural Selection: • Surviving offspring will live to pass on their helpful traits to their offspring. • This cycle of passing on the helpful traits keeps on going • The environment has “selected” individuals with the necessary traits for survival • Over long periods of time – this can lead to change

Example of Natural Selection: • New predator is introduced into an environment • Those that can outrun the predator will survive • They will be able to pass on their “fastrunning” genes on to their offspring. • The slow runners will slowly disappear…. . why? • Over LONG periods of time, the entire species will have the “fast-running” gene.

How does a new species form? • Variations can lead to a new species • Geographic isolation – complete separation from the original species – River, volcano, mountain range, storm washing animals into sea and eventually landing on an island, earthquake • Once isolated, the members of a species can no longer mate with the original group • Accumulation of different traits

Continental Drift…. • Pangaea – supercontinent • Over millions of years, Pangaea gradually drifted apart due to continental drift (convection currents) • Climates changed • Species became isolated from one another • Natural selection occurred • Example: Australia Marsupials

Fossil Record

What is a fossil? • In order to understand what occurred long ago, scientists act like detectives to solve clues…. using fossils! • Fossil – preserved remains or traces of an organism that lived in the past. – Bone, tooth, shell, footprints, worm burrows, etc…. . – Formed when organisms become buried under sediments after they die.

Determining a Fossils age…. . • The age of a fossil can be used to reconstruct the history of life on earth. • Relative Dating: Looking at the layers of rock top layer is the newest, bottom layer is the oldest. • Absolute Dating: Using the actual radioactive elements found in the fossils

Fossil Record: • The millions of fossils that scientists have collected are called the fossil record. • Almost all of the species preserved as fossils are now extinct. • Extinct – NO members of a species are still alive • Scientists use the fossils and foot prints to rebuild and understand the creature • Provides evidence about WHEN different kinds of organisms may have lived on earth. • Estimate ages of fossils – created a “calendar” of events that date back 4. 6 billion years!! – Geological Time Scale

Incomplete Fossil Record • The fossil record is incomplete because most organisms that died did not leave behind fossils. • These gaps have left many unanswered questions. • Scientists do not know how rapidly species change.

Causes of extinction: • Changes in environmental conditions can affect the survival of species.

Causes of extinction: • Natural events • Major changes in climate • An asteroid threw huge clouds of dust and gas into the atmosphere • The dust clouds blocked the sunlight, making the climate cooler and killing plants. • Herbivores died • Carnivores died • Massive volcanic eruptions

Causes of extinction: • • • Human activities Habitat destruction Loss of environment Pollution Hunting and killing too many of a species

Other Evidence of Change

Similarities in body structure: • Scientists compare body structures of living organisms • Body structures: basic body plan – How the bones are arranged – Organ systems • Fish, amphibians, reptiles, birds and mammals all have similar body plans. – Internal skeleton with a backbone

Homologous structures: Scientists use the similar structures of forelimbs as evidence that these three organisms share a common ancestor.

Similarities in early devolvement • Scientists also make inferences about evolutionary relationships by comparing the early development of different organisms. • Compare a bird, frog and rat…. . very different right? • HOWEVER, during early development, these organisms have some similarities.

Similarities in DNA: • Scientists compare genes of different species to determine possible relationships among species. • Compare DNA • More similar two species DNA is, the more closely related they are – Horse and zebra – Lion and tiger – Cat and dog?

Combining the Evidence: • Scientists have combined evidence from fossils, body structures, early development, and DNA … – Example: Scientists have inferred that dogs were more closely related to wolves than to coyotes based on similarities in body structure, DNA and early development. • Branching Tree – a diagram that shows how scientists think different groups of organisms are related. Common Ancestor