Theory of Evolution Just how do species change over time???? Early atmosphere, evidence, natural selection and disease agents influence natural selection.

Introduction Evolution “ simple” definition: change over time Evolution helps us to understand the history of life.

Central idea The central idea of biological evolution is that all life on Earth shares a common ancestor, just as you and your cousins share a common grandmother

Evidence for Evolution Adaptations Fossil Record Comparative Anatomy Embryological Development DNA Similarities

Adaptations All organisms have adaptations which help them survive in their particular environment Adaptation: a structure or behavior that helps an organism better survive in its environment Examples: Mimicry, camouflage and physiological

Mimicry Mimicry: a structural adaptation that enables one species to resemble another species E.g. A harmless species might mimic a poisonous one

Camouflage Camouflage: a structural adaptation that allows a species to blend in with its surroundings

Physiological Adaptations Many bacteria have evolved resistance to antibiotics in the last 50 years Pests have evolved resistance to pesticides

Pathogens can influence natural selection by weeding out the weaker ones Organisms with stronger immune systems are more likely to survive pathogens. Eventually, the species that builds up antibodies for this particular pathogen will thrive.          

Bacteria are also affected by Natural Selection. The bacteria that build up a resistance the antibiotics survive. The ones that do not also die, just like in animals and plants.

https://www.youtube.com/watch?feature=pla yer_embedded&v=zjR6L38yReE http://www.pbs.org/wgbh/evolution/library/ 10/4/quicktime/l_104_03.html

Variation in Populations Evolution by natural selection happens in populations, not individuals. A single organism cannot evolve. Populations evolve. Populations evolve because there is variation Variation causes some organisms to be better fit than others. These better fit organisms are more likely to survive and pass their genes to the next generation

Evolution by Natural Selection Evolution is the gradual change in a population over time Darwin was the first scientist to realize that evolution can work by natural selection. Natural Selection – Organisms with traits well suited to an environment are more likely to survive and produce more offspring than organisms without these favorable traits “Survival of the fittest” E.g. Thicker fur is a favorable trait in cold environments

Charles Darwin (1809 – 1882) English naturalist who proposed the theory of evolution by natural selection

HMS Beagle Voyage Darwin sailed around the world on the HMS Beagle and carefully studied thousands of different plants and animals

The Galapagos Islands On the Galapagos Islands Darwin found very strange plants and animals that don’t exist anywhere else in the world!

Darwin’s Finches Different islands have different types of finches not found on any other islands. This is where species all deriving from a common ancestor have over time successfully adapted to their environment via natural selection.

Two Types of Evolution Convergent evolution: distantly related organisms evolve to become more similar Happens when unrelated species adapt to similar environments, possibly in different parts of the world

Two Types of Evolution Divergent evolution: species that once were similar become increasingly different Happens when populations adapt to different environments

Galapagos Giant Tortiose

Blue-footed Booby

Natural Selection There are 3 basic types of natural selection Directional Selection Stabilizing Selection Disruptive Selection

Directional Selection Directional selection: favors one of the extreme variations of a trait E.g. Male peacock tail feathers: Females favor larger tail feathers. Therefore males with larger feathers reproduced more often. Over many generations tail feathers grow larger and larger

Stabilizing Selection Stabilizing selection: favors average individuals in a population E.g. Human infants: Too small = bad; too large = bad; average = good

Disruptive Selection Disruptive selection: favors individuals with either extreme of a trait but intermediate individuals have a disadvantage E.g. Cuddlefish (a type of squid): Being large is an advantage because females prefer larger males. Being small is an advantage also. Small males impersonate females trick the females into mating.

Early Atmosphere conditions Atmosphere contained all of the following gases: Nitrogen Ammonia Methane Carbon Dioxide Water Hydrogen No oxygen….oxygen came later with photosynthesis.

How did the first cells evolve? Experiment conducted by Miller and Urey proposed simple- organic molecules could have been synthesized in the atmosphere of early Earth and rained down into the oceans.

Fossil Evidence Fossil: Any trace of a dead organism Fossils show the evolution of species over the past millions of years Fossil evidence proves that modern species have evolved from ancient species

Puijila the walking seal

Tiktaalik

Archaeopteryx

Comparative Anatomy Homologous structures: Body structures on different organisms that are similar in structure (same bones) and evolved from a common ancestor

Homologous Structures

Comparative Anatomy Analogous structures: Body structures on different organisms that are similar in function but did not evolve from the same ancestor (bird wing and butterfly wing)

Moth (insect) Pterodactyl (reptile) Bat (mammal) Bird Analogous Wing Structures

Comparative Anatomy Vestigial structure: body structure in an organism that no longer serves its original purpose but was useful to an ancestor (useless wings on the African ostrich)

Embryological Development Early in development, human embryos and embryos of all other vertebrates are very similar, which suggests that all vertebrates are related

DNA Similarities Nearly all organisms have DNA, ATP, and many of the same proteins and enzymes The DNA (genes) of closely related organisms looks very similar

What Drives Evolution? Mutations Genetic Drift Gene Flow Natural Selection

Gene Pool Gene pool: collectively, all of the alleles of the population’s genes Allelic frequency: the percentage of any specific allele in the gene pool Genes can enter and leave a population’s gene pool for many reasons Populations in which the gene pool is not changing are said to be in genetic equilibrium

Mutations New genes can be added to the population by errors in DNA copying called mutations Most mutations are neutral or bad!

Mutations Very very rarely a mutation might come along that improves an organism’s chance at survival or reproduction These mutant genes will be passed along to offspring and become more common in the gene pool over time If the mutation offers a large advantage, eventually (after many generations) all members of the population will have the beneficial mutation

Evolution by Artificial Selection Artificial Selection: Humans choose individuals with certain traits for breeding After many generations of selection, dramatic evolutionary changes can result Dogs Fruits/Vegetables Livestock

Gene Flow Gene flow: the transport of genes by traveling individuals When an individual leaves a population, its genes are lost from the gene pool When an individual enters a population, its genes are added to the gene pool

Genetic Drift Genetic drift: when allelic frequencies are changed by random events in a isolated population Example: diseases, natural disasters, mating habits

Speciation-the evolution of a new species A certain population may become isolated and evolve to fit new or different environmental conditions The isolated population may change so much that it can no longer mate with the original population Similar to the evolution of new languages

How Fast Does Speciation Occur? Gradualism: idea that species originate through a gradual change of adaptations (longer than 10,000 years) E.g. Fossil evidence shows that sea lilies evolved slowly and steadily over time Punctuated equilibrium: idea that species originate in rapid bursts (10,000 years or less) with long periods of genetic equilibrium in between Global ice age causes rapid adaptation of thick fur Both gradualism and punctuated equilibrium are known to occur