Evolution and Natural Selection

 Aristotle, others observed & studied patterns of living things  Alfred Wallace—(Mid 1800s) Studied patterns of where species lived & how they might be related  Biogeography—study of patterns in the geographic distributions of species and communities  Comparative Morphology—study of similarities in structures of different species

 Rhea—South America  Emu—Australia  Ostrich—Africa

 Biogeography—why were some animals and plants similar in different parts of the world?  Comparative morphology—Why were anatomical structures of different animals similar?  Fossils—Why were deeper layers unlike modern species and higher layers more like modern species?

 Georges Cuvier—Noted that dramatic changes happened in fossil species. Theorized that survivors repopulated the earth after great catastrophes.  Jean Lamarck—Offspring inherit traits that a parent acquires in its lifetime.

 Darwin attended Cambridge University to study theology, had an interest in natural history  1831—Darwin voyaged on HMS Beagle as a naturalist  Read theories challenging the geographical age of the earth  Noticed differences in species

 When returned to England, studied notes and specimens  Noticed that there are similarities between species, and between living species and fossils  Deduced that any population can produce more individuals than the environment can support. Who lives and who dies?  Noticed that some modifications of traits allow individuals within a species to have a greater chance of survival

 Descent with modification— traits are modified, then passed along to offspring and down generations  Natural selection—differences in reproduction of individuals within a population based on characteristics related to survival

 1859—On the Origin of Species published.  Outlined theory of evolution (descent with modification) based on natural selection  Created great controversy immediately!

 There are slight variations in traits of a species.  These traits are inheritable.  Some of these traits increase an organism’s chances of survival and reproduction.  Those individuals who survive and reproduce pass along their genetic material (“survival of the fittest”).  The offspring are more likely to have the variation of the trait that allowed better survival & reproduction.  Natural selection—individuals with beneficial traits are more likely to survive and pass on these traits

 With each generation, there are slight modifications in traits.  Over enough time, modifications accumulate so that eventually the population is very different from the ancestral organisms.  Darwin theorized a gradual, continual change

 Origin of life  4.4 billion years ago  Began with simple chemicals, gradually became more complex through bonding  Eventually these formed amino acids  As polypeptides formed, eventually became simple life  Primitive organisms in ancient oceans

 Natural selection resulted in more complex single-celled organisms  Benefit to working together  These eventually evolved into multi- celled organisms  Organisms changed based on evolutionary pressures

 Organisms starting moving onto land  Those who had traits that increased their survival on land evolved  Organisms continued to evolve and modify based on environmental pressures  Most “fit” of each generation would survive

 Fossilization  Organism becomes covered in sediments or ash  Minerals absorb into bones & tissues  Pressure builds, furthering conversion to minerals  “Soft” tissues not well preserved

 Stratification  Layers of rock formed by deposits of volcanic ash, silt, sand, etc.  Older layers deeper, newer layers build up on top

 Radiometric dating  Measure proportions of an isotope in a mineral  Predictable deterioration of isotope, so based on amounts can determine how long since it was formed

 Older fossils show fewer variety of organisms  Older fossils show more primitive features  Newer fossils show changes and progression among characteristics  New characteristics appear in newer fossils  The complexity of organisms increases when looking at newer versus older fossils

 Transitional forms  “Missing links”  Archaeopteryx  Eustheopteron  Seymouria

 Problems?  Radiocarbon dating may not be accurate Assuming no or limited “daughter” isotopes in parent Assuming constant rate of decay Inaccuracies have been calculated (dating volcanic rock known to be 200 years old as billions of years old)  Some transitional forms questioned Archaeopteryx likely an extinct species and not a bird ancestor  Fewer than expected transitional forms  Living, unevolved “fossils” Coelacanth— “extinct” 80 million years ago, rediscovered 1938

 Problems?  Cambrian “explosion” Sudden appearance of numerous fully-formed species of organisms No transitional forms prior to that No evidence of Darwininan gradualism

 Several experiments have created simple organic molecules under “primitive Earth” conditions  “Building blocks” for life  Fossilized bacteria  Living multicellular colonies  Portuguese Man o’ War

 Problems?  Dispute and debate over conditions of primitive Earth  No proven mechanism for evolving from simple compounds to primitive cells  Spontaneous generation? “Life” from “unlife”  Many theories, often conflicting  Really an unanswered question

 Homologous structures—similarities in body parts between groups.  Morphological divergence—Variations in structures of different species based on a basic form in a common ancestor

 Problems?  Different genes can produce homologous structures Body segments in fruit flies and wasps  The same gene can produce non-homologous structures

 Similar species in different parts of the world  Rheas, emus, ostriches  Common ancestor, separated because of plate tectonics (movement of sections of the earth’s crust)

 Theory—mutations of DNA (insertion, deletion, inversion, translocation, duplication, etc.) can result in new traits or features. These are random events  If these new features give the organism a survival advantage, they are more likely to be passed along.

 Mutations do happen (well established)  Mutations can be beneficial  Bacterial resistance to antibiotics  Sickle cell anemia giving resistance to malaria  Resistance to atherosclerosis in Italian village

 Problems?  Virtually all mutations are harmful or neutral  Many new traits created in lab are not seen in the wild (fruit flies)  New structures do not mean benefit Second pair of fruit fly wings lack muscles and harm flight ability  Truly beneficial mutations only found in bacteria & other single-celled organisms  Beneficial “mutations” often can be argued to be recessive traits that already exist  Mutations really beneficial? Sickle-cell anemia

 Similar DNA sequences in many species  The more closely they appear to be related, the more DNA is shared  Humans & bananas: 50-60%  Humans & worms: 75%  Humans & chimpanzees: 98%  The less DNA in common, the more distant the common ancestor

 Proteins also show similarities between species  Cytochrome C (part of electron transfer) Present in all living organisms, great similarity  Said to have been “conserved” across species as evolution took place

 Problems?  Small differences in DNA can mean big differences in appearance & function  Some similarities do not have evolutionary progression (“lower” to “higher” organisms) Cytochrome C  Similarities could result from similar actions & functions, in the same way that sports cars share similarities with each other, but not with SUVs

 Populations evolve, not organisms  Phenotypic variation  Morphological—physical features  Physiological—metabolic activities and products  Behavioral—responses to situations and stimuli  Gene pool—possible trait variations within a population

 Mutation changes or creates new alleles  Other factors shuffle existing alleles  Crossing over (Meiosis I)  Homologous chromosome arrangement (Meiosis I)  Fertilization  Some alleles have greater frequencies in the population than others  Red hair  Albinism  Allele frequencies can change over time

 Natural selection— “Survival of the fittest”. Some traits allow individuals to survive or reproduce better than others. These traits therefore increase in a population.  Three types  Directional  Stabilizing  Disruptive

 Directional selection— Natural selection “favors” a phenotype, increasing the frequency of this allele  Peppered Moth  Two variant phenotypes  Pre-industrial, light were more common  After industrial pollution, dark were more common

 Stabilizing selection—Intermediate forms of a trait are favored, extreme forms are not  Human birth weight  Very large or very small babies less likely to survive compared to average-sized

 Disruptive selection—Extreme forms of variation are favored, intermediate forms selected against  “Darwin’s” finches  Speculated to be derived from common ancestor  Different beaks adapted for different foods

 Natural selection (“microevolution”) is readily accepted, even by critics  “Classic” examples not unchallenged  Questions of validity of peppered moth studies  Galapagos finches show variations in bills, but return to “normal”

 Ernst Haeckel—in mid 1800s first theorized that as embryos develop, they go through their evolutionary development  Early embryos look very alike because of common descent

 Haeckel faked his drawings!  This was detected in his lifetime  Recently discussed again  But still in some texts (below from 2002)

 Most scientists recognize that Haeckel was wrong  Embryos not as similar in early development

 Problems?  Haeckel’s theory disproven, but still sometimes used  Embryos not very similar, easy to distinguish  Some very large differences in embryos, arguably more than similarities  Really no problems?  Embryos do share some similar traits (just not to the degree of Haeckel) Pharyngeal pouches Tails  Development patterns are similar

 Scientists overwhelmingly support evolution  Much is still not understood about the processes involved  Many intelligent, non-religious people have problems with aspects of evolutionary theory  Darwin’s theories have always been challenged  Much evidence for AND against evolution  Decisions need to be made on facts and science

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