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| WHAT IS BIOLOGICAL EVOLUTON? | Changes in the genetic makeup of a population of organisms over time • It is the central theme biology • All species arise from other, pre-existing species. However, through time they accumulate differences such that ancestral and descendant species are NOT IDENTICAL. • Darwin used the phrase “Descent with modification” to explain this concept |
| Historical development of evolutionary thought | • Early Greek philosophers:- Anaximander (about 2500 years ago) Life arose in water and simpler forms preceded more complex forms. • Aristotle believed that species were fixed and did not evolve. • Judeo-Christian tradition:- All species were created in a single act of creation about 6000 years ago! • Buffon (mid 1700) Observed similarities between fossils and living species. He suggested that earth was much older and raised the possibility that different species arose from common ancestors. He also believed in catastrophism. • Lamark (early 1800) was the first to support the idea of evolution strongly, but he believed the mechanism for change was the inheritance of acquired characteristics. |
| LAMARCK’S TRANSFORMATION THEORY | suggested that organisms evolved by the process of adaptation. Also suggested some erroneous ideas such as the inheritance of acquired characteristics. i.e. Effects of unique events get passed on to offspring. |
| FATHERS OF THEORY OF NATURAL SELECTION | • Charles Darwin (Born 1809) (200th B’day 2009) • Alfred Russell Wallace • Patrick Matthew |
| Charles Lyell | Principles of Geology |
| The Voyage of the Beagle | In December 1831, Darwin left Great Britain on the HMS Beagle to explore the world. – On his journey on the Beagle, Darwin Collected thousands of specimens. Observed various adaptations in organisms. Darwin’s finches • Are an excellent example of Natural Selection and Adaptive Evolution. |
| Descent with Modification | Darwin made two main points in The Origin of Species: • Organisms inhabiting earth today descended from ancestral species. • Natural selection was the mechanism for descent with modification. |
| REMEMBER……. | •When we speak of evolution, we mean change across but not within generations. • The latter is referred to as ontogeny. •Ontogeny can reveal phylogeny |
| Darwin based his theory of natural selection on two key observations... | Observation 1: Overproduction • All species tend to produce excessive numbers (got the idea from the economist Malthus) • This leads to a struggle for existence (also from Malthus). A fungus: Puff Ball producing large number of spores (reproductive units) Observation 2: Individual variation • Variation exists among individuals in a population. • Much of this variation is heritable. |
| WHAT IS ADAPTATION? | Adaptation is a universal characteristic of living things. • Definition: Properties of an organism that allow it to survive and reproduce. |
| Fossils | Are preserved remnants or impressions left by organisms that lived in the past which are often found in sedimentary rocks. Paleontologists (scientists who study fossils) have discovered many transitional forms that link past and present. • Have traits common to an ancestral group and its presumed derived descendants. – Transitional fossils imply that • birds descended from one branch of dinosaurs (light-boned, evolved to hop, and gradually to fly) • whales descended from four-legged land mammals. |
| The chronological order of which different vertebrate groups appear in fossil records | Fishes Amphibians Reptiles Birds Mammals |
| Biogeography | • Is the study of the geographic distribution of species. • First suggested by Darwin that today’s organisms evolved from ancestral forms. • Many examples from biogeography support evolutionary theory. |
| Comparative anatomy | • Is the comparison of body structure between different species. • Confirms that evolution is a remodeling process (Editing but NOT a Creating process). |
| Homology vs Analogy | • Homology: Is the similarity in structures due to common ancestry • Analogy : Similarity in structures but NOT from common (recent) ancestry |
| Comparative anatomy – Divergent evolution | Homologous structures have a similarity due to common ancestry • Evolved by divergent evolution: divergence from a common ancestral structure or function. – e.g., remodeling of the pattern of bones forming the forelimbs of mammals for different functions. |
| Comparative anatomy – Convergent evolution | Analogous structures have a similar form or function but evolved independently of each other. • Evolved by convergent evolution: independent evolution of similar features in species of different lineages. – e.g., Flying insects, birds, and bats have all evolved the capacity of flight independently. They have "converged" on this useful trait (formation of wings). » Birds (feathers attach to forelimb bones) » Insects (outgrowth of exoskeleton) » Bat wing membranes (webbed digits) |
| Analogous Structures | Different ancestry but have the same or almost the same form and function: Convergent evolution |
| Comparative anatomy: Adaptive radiation | Adaptive radiation is the rapid evolutionary diversification of a single ancestral lineage, resulting in speciation (many species evolve from a single lineage). It occurs when members of a single species occupy different niches with different environmental selection pressures, resulting in morphological adaptations as a result of natural selection. |
| Comparative anatomy | Vestigial structures: are remnants of features that served important functions in an organism’ s ancestors and |
| ______ & _______ bones evident in ancient whale fossils | Pelvis and rear leg bones |
| Comparative Embryology | Comparative embryology is the comparison of structures that appear during the development of different organisms. – Comparative embryology of vertebrates supports evolutionary theory. (Oncogeny reveals phylogeny) |
| Molecular Biology | Evolutionary relationships (Phylogenetic reletionships) among species Leave signs in DNA and proteins (immunology). – Can be determined by comparing genes and proteins of different organisms. Universality of the genetic code is the strongest evidence that all life is related Similarities in amino acid sequences Antigen antibody reactions |
| Darwin: Evolutionary trees | Darwin saw the history of life as analogous to a tree. – The first forms of life on Earth form the common trunk. – At each fork is the last common ancestor to all the branches extending from that fork. – The tips of millions of twigs represent the species living today. |
| Darwin's theory and the modern synthesis | The science of genetic changes in populations, in 1920 was an important turning point for the theory of evolution. Genetics provided the missing links of how traits were inherited from one generation to the next. A theory of evolution that includes genetics was developed in 1940s. It focuses on POPULATIONS as the units of evolution |
| A population is a... | group of individuals of the same species, living in the same place at the same time |
| Garter snake evolution in response to predators: Remember spotted vs stripes | Natural selection can affect an individual’s survival and reproductive success, but the evolutionary impact is only apparent in the heritable genetic changes in a population over time |
| WHAT IS MICROEVOLUTION? | Microevolution is change in a population’s gene pool over time A population’s gene pool consists of all the alleles in all the individuals making up the population. |
| Genotype frequency | Proportions or percentage of a genotype in a population. |
| Allele frequency: | Proportions or percentage of an allele in a population. |
| Microevolution is the changes in allele frequencies that occur over time within a population, due to | Gene mutation and sexual recombination – Gene flow – Genetic drift (random change, bottleneck effect, founder effect) – Selection (natural and artificial) |
| Five factors which cause populations to evolve are | 1. Mutation 2. Non-random mating 3. Gene flow 4. Genetic drift 5. Natural Selection |
| Sources of genetic variation | mutations: changes in the nucleotide sequence of DNA sexual recombination: the shuffling of alleles during meiosis and fertilization |
| Genetic drift is a | change in the frequency of an allele in a small population due to: – random change, bottleneck effect, founder effect - decreases the overall genetic variability - results in a loss of individual variation and hence loss of adaptability |
| Gene flow | is genetic exchange with another population, that may result in the gain or loss of alleles, and tends to reduce genetic differences between populations. – Can occur between species (hybridization; horizontal gene flow) Microevolution: Gene flow Examples: • Pollen (gamete) dispersal between populations • Global movements of humans |
| Natural selection IN TERMS OF MICROEVOLUTION* | Of all causes of micro evolution, only natural selection promotes adaptation due to unequal reproductive success of individuals. |
| Three general outcomes of natural selection | Directional selection shifts the overall makeup of a population by selecting in favor of one extreme phenotype. Disruptive selection can lead to a balance between two or more contrasting phenotypic forms in a population 3. Stabilizing selection favors intermediate phenotypes, occurs in relatively stable environments, and is the most common |
| Sexual dimorphism | is a distinction in appearance between males and females. |
| Sexual selection | is a form of natural selection in which individuals out-reproduce others in a population because they have greater success in securing mates. |
| The origin of species | The diversity of life evolved through speciation, the process in which one species splits into two or more species |
| The biological species concept defines a species as | “A group of populations whose members have the potential to interbreed with one another in nature to produce fertile offspring |
| Prezygotic barriers | prevent mating or fertilization between species. |
| The species concept is based on | reproductive compatibility rather than physical similarity. |
| Reproductive barriers between species | Temporal Isolation Habitat Isolation Behavioral Isolation Mechanical Isolation Gametic Isolation |
| Postzygotic barriers | operate if interspecies mating occurs and hybrid zygotes form. |
| Reduced Hybrid Viability | Frail or partially developed hybrid salamander offspring do not survive long enough to reproduce. |
| Reproductive barriers between closely related species | |
| Mechanisms of speciation | – A key event in the potential origin of a species occurs when a population is somehow cut off from other populations of the parent species. – Species can form by • Allopatric speciation, due to geographic isolation, or • sympatric speciation, without geographic isolation |
| Allopatric speciation of antelope squirrels | Geological isolation of squirrel populations on opposite rims of the Grand Canyon Speciation occurs with the evolution of reproductive barriers between the isolated population and its parent population. – Even if the two populations should come back into contact at some later time, the reproductive barriers will keep them as separate species. |
| Sympatric speciation | Sympatric speciation occurs in populations that live in the same geographic area. – An accident during cell division (mitosis or meiosis) that results in an extra set of chromosomes is a common route to sympatric speciation in plants. – Many polyploid species arise from the hybridization of two parent species. Domesticated species: oats, potatoes, bananas, peanuts, apples, sugarcane, coffee, wheat |
| Sympatric speciation: Polyploidy | Polyploidy (e.g., 4n) can arise by meiotic failure and self-fertilization resulting in fusion of unreduced gametes (e.g., 2n instead of n). |
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