Chapter 15 – Evolution: Theory & Evidence

Theories of Evolution Jean Baptiste Lamarck Proposed that similar species descended from a common ancestor Acquired Traits – Hypothesized that organisms “picked up” traits during their lifetime

I really want some leaves! Lamarck’s theory At first, there are only short-necked giraffes. They try harder to reach the leaves.

So their necks get longer because they use them more. I really want some leaves! Lamarck’s theory So their necks get longer because they use them more.

Lamarck’s theory

Lamarck’s theory

And then their babies have long necks, too! Lamarck’s theory And then their babies have long necks, too!

Darwin’s theory At first, there are some long-necked giraffes and some short-necked giraffes. Only the long necked can reach the leaves.

The short-necked giraffes are more likely to die of hunger. Darwin’s theory The short-necked giraffes are more likely to die of hunger.

Darwin’s theory The long necked giraffes have babies that will also have long necks when they grow up.

Write/Pair/Share What is another possible reason for giraffe necks to have evolved for length? Write at least 2 lines!

Natural Selection Charles Darwin & Alfred Wallace both suggested the theory of natural selection Natural Selection – organisms best suited for the environment reproduce more successfully than others The favorable trait increases in a population Making a population the smallest unit able to evolve

Charles Darwin H.M.S. Beagle Read books by Charles Lyell (geologist) placing an emphasis on uniformitarianism Darwin observed various habitats and considered that these changes of earth played a part in the adaptation of organisms

Darwin’s Data Traveled all over the world Galapagos Islands Collected species of all types of animals Compared animals from each destination Galapagos Islands Collected beetles and finches 13 species of finches Observed tortoises

Darwin’s Finches Based theories on the 13 species of finches collected in the Galapagos Hypothesized that the finches all evolved from a common ancestor (originating in South America) The environments of each island produced different challenges The finches would have to overcome these different environments to survive.

Darwin’s Theories Descent with Modification Newer forms in the fossil record are modified descendants of older species Reproduction allows species to change over time Proposed that ALL organisms descended from a few ancestors with changes

Natural Selection HOW descent with modification occurs Influenced by Thomas Malthus Populations can double and redouble Human population is limited by adverse conditions Theorized that the environment was the limiting factor for populations Some organisms have traits that make them better fit to respond to certain environmental pressures Organisms better fit reproduce more and pass on the favorable traits Individuals in a population would respond to environmental changes differently because they are not identical A population adapts BECAUSE the favorable trait from a few individuals is passed down

REMEMBER Natural selection is not an ACTIVE process Meaning that you can’t MAKE yourself change Traits (ALLELES) MUST be present in a population for evolution to occur Variation exists among individuals in a species. Individuals of species will compete for resources Some competition would lead to the death of some individuals while others would survive Individuals that had advantageous variations are more likely to survive and reproduce.

Evidence of Evolution The Fossil Record What is a fossil? A fossil is the remnants of an organism Found in sedimentary rock Types of fossils: Mold – imprint in rock in the shape of the organism Cast – a rock-like model of the organism

Distribution of Fossils Nicholas Steno – Law of Superposition Successive layers of rock or soil were deposited on top of one another Lowest strata (stratum) is the oldest Observing these strata allows them to determine the relative age of a fossil and the absolute age

Studying Fossils The fossil record tells us that organisms appeared for awhile and then died off Mass Extinctions Evidence in fossils shows us that there are periods where large numbers of species disappeared Caused by environmental changes

Transitional Species Organisms that have features that are intermediate between hypothesized ancestors and current species. Hypothesis that whales descended from land mammals based on a sequence of transitional forms.

Don’t believe me??? Whale Evolution

This is what Darwin did with the finches, turtles and beetles!!! Biogeography Scientists study the distribution of fossils and living relatives to help determine how organisms have changed Similarities between fossils and living organisms allows us to make connections with our ancestors This is what Darwin did with the finches, turtles and beetles!!!

Comparative Anatomy & Physiology Examining the structure & function of organisms Homologous Structures Same structure but has a different function Evolved from a common ancestor

Analogous Structure Same function but different structure Evolved from a different ancestor but faced similar pressures

Vestigial Structures Organ or structure that was useful to an ancestor but now has no use to the current organism Examples Appendix in humans Pelvic and limb bones in snakes Leg bones in whales

Macromolecules Genetic Evidence Embryology Examination of major macromolecules in organisms (specifically proteins) Genetic Evidence DNA and RNA - Similarities in these molecules are evidence that organisms evolve from common ancestors Embryology Early stages of development are strikingly similar in organisms The more closely the development, the more closely they are related

Fish, salamander, tortoise, chick, hog, calf, rabbit and human

Evolution in Action Interactions between species and environmental pressures continue to drive evolution

Types of Evolution Co evolution – Change of two or more species in close association with each other Predators and prey, parasites and hosts Flowers and pollinators

Darwin’s Orchid Darwin’s Moth

Convergent Evolution– unrelated species evolve due to similar environmental pressures Shark and porpoise, bird and bee

Divergent Evolution – two or more related species evolve from a common ancestor Species DIVERGE (separate) Adaptive radiation – many species evolve from a common ancestor Artificial selection – divergence is sped up by choosing the parents of offspring (found in dogs)

Parallel Evolution Similar to convergent but this happens in SAME environment When two different species in the same type of environment develop the same adaptations for survival, it is considered parallel evolution