EL41: Evolution and Extinction of Life on Earth

Transcription

1 EL41: Evolution and Extinction of Life on Earth Lecture 1.2. How biological evolution works Lecture Overview! Topics: Darwinian evolution Adaptations help organisms survive. Recently discovered aspects of evolution.! Further Reading: Evolution in Minutes, Dr. Darren Naish,

2 Key Learnings:! Key Learning #1:. Charles Darwin first proposed his theory of evolution over 150 years ago and this theory has now become a major paradigm in biology. Descent with modification - species change over time, all organisms share a common ancestor, and evolutionary change generally happens slowly.! Key Learning #2: Organisms with stable and abundant populations have adaptations that allow them to survive and thrive in a particular environment.! Key Learning #3: Since Darwin s time, scientists have discovered many new aspects of evolution, including; speciation, biodiversity, macro and micro evolution, pace of evolution not always slow, sexual selection, and living fossils. Key Learnings:! Key Learning #1:. Charles Darwin first proposed his theory of evolution over 150 years ago and this theory has now become a major paradigm in biology. Descent with modification - species change over time, all organisms share a common ancestor, and evolutionary change generally happens slowly.! Key Learning #2: Organisms with stable and abundant populations have adaptations that allow them to survive and thrive in a particular environment.! Key Learning #3: Since Darwin s time, scientists have discovered many new aspects of evolution, including; speciation, biodiversity, macro and micro evolution, pace of evolution not always slow, sexual selection, and living fossils. 2

3 Seven ages of the cosmos Eric Chaisson, fr_1_site_summary.html The Origin of Species! Darwin explained three broad observations: The unity of life The diversity of life The match between organisms and their environment 2011 Pearson Education, Inc. 3

4 Darwinian Evolution The Basics ( Nothing in biology makes sense EXCEPT in the light of evolution. Theodosius Dobzhansky) God s Kitchen! Descent with modification & all organisms share common ancestors with other organisms! Evolutionary change is gradual and slow [generally]! There is no intention or progress in evolution a mindless process of whatever works! 7 Descent with Modification! Darwin noted that current species are descendants of ancestral species Evolution can be defined by Darwin s phrase descent with modification (refers to the view that all organisms are related through descent from an ancestor that lived in the remote past)! Evolution can be viewed as both a pattern and a process 2011 Pearson Education, Inc. 4

5 Descent with modification en.wikipedia.org/wiki/ Image:Phylogenetic_tree.svg! Descent with modification all living things share a common ancestor.! We can draw a Tree of Life to show how every species is related,! BUT, humans are not the pinnacle of this tree!! Evolution is the process by which one species gives rise to another and the Tree of Life grow. Descent with modification: the modern bush of life 5

6 Descent with modification: simplified bushes 6

7 Darwin s theory of natural section! Variation: There is variation in populations & some of these traits are heritable.! Overpopulation: More individuals are typically born into a population than can survive.! Competition: There is competition for limited resources available to them to grow, survive and reproduce.! Natural Selection: Some variation gives some individuals a slight survival advantage favourable traits. Individuals that do survive are better adapted - in a given environment and will be naturally selected to survive longer and leave more offspring that share successful adaptations for that environment.! Evolution & Speciation: over time, natural selection will cause new species to evolve adaptations that are particularly well suited for survival and reproduction in a given environment 14 7

8 Variation: Members of a population often vary in their inherited traits 2011 Pearson Education, Inc. 8

9 Variation Some mutations will persist and increase genetic variation within a population. Variants of a particular gene are known as alleles. For example, the one of the genes for hair colour comprises brown/blonde alleles and arose in northern latitudes. majorityrights.com/index.php/weblog/comments/ racial_variation_in_some_parts_of_the_skull_involved_in_che wing/ 17 Variation: All in the Genes The genetic make-up of an organism is known as its genotype. An organism s genotype and the environment in which it lives determines its total characteristic traits i.e. its phenotype. Genotype Phenotype 18 commons.wikimedia.org/wiki/image:dna_double_helix_vertikal.png 9

10 Variation: DNA The double-helix structure of DNA was discovered in Watson and Crick and their model of DNA DNA replication This showed how genetic information is transferred from one cell to another almost without error. WatsonCrick.jpg en.wikipedia.org/wiki/dna 19 10

11 DNA mrna - Proteins Creating Genetic Diversity! Genes- physical locations on chromosomes within each cell of an organism.! Genotype- the complete set of genes in an individual.! Mutation- a random change in the genetic code.! Phenotype- the actual set of traits expressed in an individual. 11

12 Mutations Types of mutation However, occasional mutations or copying errors can and do occur when DNA is replicated. Mutations may be caused by radiation, viruses, lateral gene transfer & carcinogens. Mutant fruitfly Mutations are rare and often have damaging effects. Consequently organisms have special enzymes whose job it is to repair faulty DNA. 23 upload.wikimedia.org/wikipedia/commons/7/79/types-of-mutation.png humansystemstherapeutics.com/bb.htm Evolution by Random Processes! Mutation- occur randomly and can add to the genetic variation of a population.! Genetic drift- change in the genetic composition of a population over time as a result of random mating.! Bottleneck effect- a reduction in the genetic diversity of a population caused by a reduction in its size.! Founder effect- a change in a population descended from a small number of colonizing individuals. 12

13 Random Processes Random Processes 13

14 Natural Selection: Peppered Moth Haldane and the peppered moth # " en.wikipedia.org/wiki/image:biston.betularia.f.carbonaria.7209.jpg en.wikipedia.org/wiki/j._b._s._haldane The Peppered Moth is an example of Natural Selection in action discovered by Haldane During the Industrial Revolution the trees on which the moth rested became soot-covered. This selected against the allele for pale colour in the population (which were poorly camouflaged from predators) and selected for the dark colour allele 27 Natural selection acts on genetic variation! Directional selection = drives a feature in one direction! Stabilizing selection = produces intermediate traits, preserving the status quo! Disruptive selection = traits diverge in two or more directions If the environment changes, a trait may no longer be adaptive Think Extinction Events! 14

15 Natural Selection: alleles Selection of dark gene Mutant alleles spread through a population by sexual reproduction. If an allele exerts a harmful effect, it will reduce the ability of the individual to reproduce and the allele will probably be removed from the population. en.wikipedia.org/wiki/image:mutation_and_selection_diagram.svg In contrast, mutants with favorable traits are preferentially passed on said to be adaptive 29 15

16 Mechanism (5): In a nutshell 16

17 ! Overpopulation: All species can produce more offspring than the environment can support, and many of these offspring fail to survive and reproduce Stable environments, prone to extinction Sunfish: can produce Up to 300 million eggs at a time. A few will survive to adulthood and reproduce 2011 Pearson Education, Inc. Competition (or co-operation) for limited resources. 17

18 Natural and Anthropogenic selection for smaller size Artificial Anthropogenic Selection Selection for apical (tip) bud Cabbage Brussels sprouts Selection for axillary (side) buds Broccoli Selection for flowers and stems Kale Selection for leaves Wild mustard Selection for stems Kohlrabi 18

19 A Quick Quiz: Are these mutations likely to be harmful or helpful to the organism? A harmful predators would note. B harmful brain not evolved to Coordinate 6 legs. Different coloration mutation? B 6 legs on a deer? Key Learnings:! Key Learning #1:. Charles Darwin first proposed his theory of evolution over 150 years ago and this theory has now become a major paradigm in biology. Descent with modification - species change over time, all organisms share a common ancestor, and evolutionary change generally happens slowly.! Key Learning #2: Organisms with stable and abundant populations have adaptations that allow them to survive and thrive in a particular environment.! Key Learning #3: Since Darwin s time, scientists have discovered many new aspects of evolution, including; speciation, biodiversity, macro and micro evolution, pace of evolution not always slow, sexual selection, and living fossils. 19

20 Darwin saw organisms adapted to their environment (a) Cactus-eater (b) Insect-eater (c) Seed-eater 20

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22 2. Chemical Adaptations 22

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24 Quick Quiz: What kind of adaptations are the following? A A behavioral (persistence hunting) B camouflage Humans running B Skin coloration 24

25 Key Learnings:! Key Learning #1:. Charles Darwin first proposed his theory of evolution over 150 years ago and this theory has now become a major paradigm in biology. Descent with modification - species change over time, all organisms share a common ancestor, and evolutionary change generally happens slowly.! Key Learning #2: Organisms with stable and abundant populations have adaptations that allow them to survive and thrive in a particular environment.! Key Learning #3: Since Darwin s time, scientists have discovered many new aspects of evolution, including; speciation, biodiversity, macro and micro evolution, pace of evolution not always slow, sexual selection, and living fossils. Macroevolution However, if two populations of a species become isolated from one another for tens of thousands of years, genetic difference may become marked. If the two populations can no-longer interbreed, new species are born. This is called Macroevolution. Macroevolution is simply the outcome of microevolution over time Darwin s Galapagos finches are an example of this process in action. Galapagos finches

26 Macro-evolution: gradualism vs. punctuated equilibrium Extinction events The pace of evolution Extinction events Long periods of stasis 26

27 Living Fossils Stromatolites (3.5 By) Dogs are wolves Microevolution Microevolution involves changes within a species. Dogs have been artificially selected for certain characteristics for many years, and different breeds have different alleles. All breeds of dog belong to the same species, Canis lupus (the wolf) so this is an example of Microevolution as no new species has resulted

28 ! Sexual selection leads to the evolution of secondary sexual characteristics! Sexual selection may produce sexual dimorphism* Sexual selection Any difference, morphological or behavioral, between males and females of the same species. 28

29 Male-Female Height Differences: sexual selection at work in humans 57! Note: that individuals do not evolve; populations evolve over time! Note: Natural selection can only increase or decrease heritable traits that already exist and vary in a population 2011 Pearson Education, Inc. 29

30 Biological Diversity $ Biological Diversity $ Number, variety and variability of Earth s organisms- 1.9 million identified $ Consists of four components: $ Genetic diversity (below) $ Species richness $ Ecosystem diversity Functional diversity 30

31 Functional Diversity The biological and chemical processes such as energy flow and matter recycling needed for the survival of species, communities, and ecosystems. Heat Chemical nutrients (carbon dioxide, oxygen, nitrogen, minerals) Solar energy Ecological Diversity The variety of terrestrial and aquatic ecosystems found in an area or on the earth. Heat Heat Decomposers (bacteria, fungi) Producers (plants) Heat Consumers (plant eaters, meat eaters) Heat Genetic Diversity The variety of genetic material within a Species Diversity The number and abundance of species present in different communities. Fig. 4-2, p

32 Speciation Today? The mosquito was introduced to the London Underground during its construction around London Underground Mosquito It became infamous in the War for attacking people sheltering from the Blitz. en.wikipedia.org/wiki/image:gb-lu-angel-southbound.jpg en.wikipedia.org/wiki/culex Studies indicate several genetic differences from its above-ground ancestors. Interbreeding between populations is difficult suggesting 64 that speciation may be occurring. 32

33 Recent human evolution Tibetans may have evolved to cope with low oxygen levels (around 15%) in the last 3,000 years. Originally, we all had brown eyes. But about 10,000 years ago, someone who lived near the Black Sea developed a genetic mutation that turned brown eyes blue., One theory is that they act as a sort of paternity test. Two blue eyed mates can not produce a brown-eyed offspring. Brains have actually been Our cultural and shrinking over the last technological evolution 30,000 years. Are we is now much more rapid getting dumber or more Tolerance to drinking nonhuman milk last 3,000 than our biological efficient? evolution 65 years?. Evolutionary Psychology First proposed by E.O. Wilson (an ant biologist), in 1970 Evolutionary Biology + Cognitive Psychology + Neurology Our mental lives and behavior reflect (in part) the evolutionary history of our species, particularly the adaptive problems that had to be solved our modern skulls house stone age minds that are evolved to increase evolutionary fitness and survival. The evolution of the our brain & mind must have been shaped by natural selection (including sexual selection) 66 33

34 Evolutionary Psychology A few examples Our disgust over incest: evolutionary drive to avoid harmful mixing of similar genes, re-enforced by cultural taboos. (studies show you are not sexually attracted to whomever you were raised with) Male jealousy over mate: male abhorrence of cuckoldry raising another male s offspring without knowing it your own genes don t survive into the future. Homicides have resulted also, infanticides by stepfathers. Related to mate guarding. 67 Quick Quiz: Do these traits seem to be a product of natural or sexual selection? A A sexual selection B natural selection with minor variations in skin and ears Different coloration in lizards (male vs. female) B Big ears and hairless skin 34

35 That s a wrap for today! 35