Zoology 117: Introductory Vertebrate Zoology PDF -Concepts of Evolution

ZOO 117: INTRODUCTORY VERTEBRATE ZOOLOGY TOPIC: CONCEPTS OF EVOLUTION BY PROF. ADIAHA A. A. UGWUMBA  THE CONCEPT OF EVOLUTION  Definition of Evolution In biology, evolution is a complex process by which characteristic features of living organisms change...

ZOO 117: INTRODUCTORY VERTEBRATE ZOOLOGY TOPIC: CONCEPTS OF EVOLUTION BY PROF. ADIAHA A. A. UGWUMBA  THE CONCEPT OF EVOLUTION  Definition of Evolution In biology, evolution is a complex process by which characteristic features of living organisms change with time as inherited features called traits are passed on from one generation to another  Modern evolutionary biology began in the middle 19th century with the growing interest and studies of: fossils and the diversity of living organisms These convinced scientists on the evolution of organisms that :  species changed with time  Brief History of Evolution Throughout history, philosophers, religious leaders and scientists have tried to explain the origin of life on earth In the early times, the most common view was that God created every organism on earth more or less as it is now – many people still hold this view today, even among scientists  THEORIES OF EVOLUTION 1. Early Theories of Evolution: That all life on earth evolved from simple organisms  Features of early times: Limited scientific knowledge Too many unanswered questions So the belief was that life on earth as we see it was created by God 2. Modern Theory of Evolution:  This originated with the Theory of Evolution of life as a process of Natural Selection This was proposed by a British Naturalist – Charles Darwin in the middle 19th Century (1859) who is known as the Father of Evolution  In 1859, Darwin published his findings in a book titled: “On the origin of species by natural selection”  In summary: Nature selects organisms that are fit and rejects those that are unfit  Darwin’s book was sensational the first 1,500 copies produced were sold in one day  This book was highly criticized at the time because: Darwin did not have evidence to support his theory e.g. he could not explain the mechanisms that caused organisms to change  Another British Naturalist Alfred Russell Wallace working independently also had the same idea of evolution by natural selection  Both presented the same theory before the Linnaean Society of London (in 1858), a year before Darwin published his book  So Alfred Rusell Wallace shares the title of Father of Evolution with Charles Darwin  Like Darwin, Wallace also had no evidence to prove the theory of evolution by natural selection  Though Darwin/Wallace’s theory of evolution lacked evidence, – it paved way for the scientists who later provided the evidence of evolution by natural selection  Later in the 19th and mid 20th century, several scientific advances revealed that : Genes are the hereditary materials So genes are the heritable traits transferred from generation to generation  Gregor Mendel, an Australian Monk was the first scientist to study inheritance on a firm scientific basis and so he is known as the Father of Inheritance. His work in 1865 revealed that: Genes are the hereditary materials transferred from generation to generation His works also revealed how genes are transferred He found that traits are inherited in a predictable manner Therefore the modern theory of evolution is a combination of Darwinian natural selection and Mendelian inheritance  Mechanisms of Evolution 3 processes are involved namely: 1. Natural Selection: This occurs because:  Heritable variation exists within populations of organisms  Organisms produce more offsprings that can survive  Offsprings produced vary in their ability to survive and reproduce Mechanisms of Evolution Contd. 2. Gene flow: This is the exchange of genes between populations which are usually of the same species and it happens during reproduction 3. Genetic drift: This is the change in allele frequency from one generation to the next  Allele frequency is the proportion of genes within the gene pool that are a particular allele  The number of organisms in a particular population carrying a particular allele determines the allele frequency  Thus genetic drift is effective for survival New molecular biology techniques compare the genetic structures of different species which enable scientists to determine evolutionary relationships between species that were previously undetectable  Today, evolution is recognized as the cornerstone of modern biology uniting various scientific fields such as:  Cell biology  Genetics  Palaeontology  Biochemistry  Ecology  Physiology  Evolution also units various fields such as:  Psychology  Medicine (for care of diseases and understanding vulnerable diseases)  Philosophy  Geology (biostratigraphic methods used to locate mineral deposits including oil and natural gas, coal  Statistics  Computer Science (evolutionary algorithms)  How do scientists study evolution? Through:  Fossils i.e. Palaeontology  Distribution of species  Anatomical similarities  Molecular similarities  Direct observation (for organisms with short life- span)  Tracing origin of life  Evolutionary Patterns of Descent Evolving populations tend to adhere to a general pattern of descent Environmental factors often determine the pattern followed 1. Divergent Evolution: This involves divergence or separation of two segments of a population - each group follows an independent and gradual process of evolutionary change and eventually looks different from each other and their ancestors  Evolutionary Patterns of Descent Cont. 2. Adaptive Radiation: This happens when divergence occurs simultaneously among a number of populations of a single species This is usually common when a species occupies a new habitat where it has little or no competition Such specializations to adapt to their various micro-habitats eventually result in genetically distinct similar looking species  Evolutionary Patterns of Descent Cont. 3. Convergent Evolution: This occurs when distantly related species occupying similar ecological niches evolve in ways that make them appear more closely related e.g. - marsupial mammals in Australia and placental counterparts in other continents strongly resemble each other - marsupial moles of Australia look very much like placental moles found in other continents, yet these animals evolved independently of one another  Evolutionary Patterns of Descent Cont. 4. Co-evolution: This occurs when two or more organisms in an ecosystem fall into evolutionary step with one another, each adapting to changes in the other in a cycle of selection and response e.g. - predator-prey relationships - flowers and their pollinating agents  Evolutionary Patterns of Descent Cont. 5. Co-operative evolution: Evolution from mutual beneficial attractions e.g. - Plants and fungi that grow on their roots - the fungi aid the plants in getting nutrients from the soil, the plants provide the fungi with sugars (i.e. food) from photosynthesis Evolutionary Lineages of Animals Generally:  it is agreed that life of animals started with protozoans ie. protists  there is strong evidence that flagellates were the first group of animals e.g flagellated cells is present in virtually all groups of animals  the view today is that metazoans i.e. Kingdom Animalia (=Metazoa) have a polyphyletic origin  Evolutionary Lineages of Animals Phylogeny: The evolutionary development and history of a species or higher taxonomic grouping of organisms Phylogenetic Tree or Evolutionary Tree: This is a branching diagram that looks like a tree showing the evolutionary relationships among various species or group of organisms - based upon similarities and differences in their physical or genetic features  There are several schemes proposed, up to 7 or more on the origin of animals  Scheme on Evolution of Animals It is believed that the earliest animals were protists Source: The MacGraw-Hill Companies Scheme on Evolution of Vertebrates It is believed that the earliest vertebrates were fishes - jawless fishes Source: Pearson Bejamin Cummings 2008