UNIT FOUR EVOLUTION NATURAL SELECTION ADAPTATION Origin of

UNIT FOUR “EVOLUTION, NATURAL SELECTION, & ADAPTATION” “Origin of Species”

Darwin and Evolution � � In 1831 Charles Darwin took a voyage around South America on a ship, the HMS Beagle He was the ship’s naturalist; He made many observations about the flora and fauna during the 5 year voyage He kept a journal of his observations that he revisited once he returned to Great Britain In the years that followed his voyage he formulated his ideas into several published works that caused people to think more about our origin as species

Darwin and Evolution � � Darwin published his ideas in a book entitled …On the Origin of Species in the late 1850’s He has since been credited with theories of evolution and natural selection Darwin was not alone though. Alfred Wallace independently asserted the same hypothesis as Darwin in reference to natural selection Wallace wrote a letter to Darwin in 1858 explaining natural selection based on his own observations in nature; this prompted Darwin to quickly publish his life’s work

Evolution, Natural Selection, & Adaptation � � � Evolution – change in the genetic composition of a population due to chance alone Natural Selection – the process by which more favorable changes in the genetic composition enhance survival and those less favorable changes decrease survival Adaptation – all individuals in a population now possess those favorable changes, and those changes are now the accepted physical characteristics of the species

Examples Of Evolution Becoming Adaptations � � � The neck of a Giraffe The speed of a Cheetah The long snout of an Anteater The white fur of a Snowshoe Hare What is your example?

Evolution versus Creationism � � Many people of faith object to theory of evolution: notion that our DNA is similar to other species and we are related Their objections are rooted in their interpretation of sacred scripture There are some faiths that do not object to theory of evolution because they believe it was “ordained by God” Why mention religion in a biology class…. . it is still a contested issue in the 2000’s

Intelligent Design � � � theory that the universe and living things were designed and created by the purposeful action of an intelligent agent Research addressing alternate hypotheses to the Theory of Evolution “Intelligent Design” is an umbrella term used for any scientific research investigating the origin of species, the earth, and the universe Intelligent Design is not Creationism is a religious belief held by protestant Christians that the earth is only several thousand years old; they interpret sacred scripture literally

Microevolution and Macroevolution � � � Microevolution – small beneficial changes in physical characteristics of a population that slowly become dominant within the entire population Macroevolution – a physical change in an entire population that causes that population to be different from other populations of that species; if the previous is the case the “changed” population is now a new species In essence, microevolution leads to macroevolution

The Importance of Variation � � Lamarck – the environment causes changes in the species Darwin – changes occur and are either beneficial or detrimental in reference to the environment The variation that leads to some physical characteristics being more adapted to the environment is the result of genetic mutations Recall that genetic mutations occur due to chance alone

Evidence for Evolution � � The most compelling form of evidence supporting theory of evolution is the presence of fossils Fossils can be present in many forms: � Fossil remains – bones (solid portions of organisms) � Trace Fossils – footprints or imprints

Evidence for Evolution � � Another type of evidence supporting theory of evolution is direct observation by scientists of “Microevolution” Microevolution can be observed in species that reproduce often and have short lifespan � Example: Drosophila melanogaster

Using Fossils To Test Theory Of Evolution � � 1. Assemble a set of fossils of a particular group of organisms 2. Date each of the fossils by analyzing the rock in which the fossils are held for the rock layers approximate ages 3. Order the fossils by their age (age of rock in which they were found) 4. Examine the fossils

Fossils Reveal Our “Family Tree” � While there are still gaps in the fossil record, clear connections do exist showing the transition between all major groups of vertebrates: � fish to amphibians � amphibians to reptiles � reptiles to birds � birds to mammals

Anatomical Record � � Homologous Structures – a physical structure that over time diverges in form and function Homologous structures lead to “Divergent Evolution” Analogous Structures – physical structures that are initially different in form and function but over time converge to have a similar form and function Analogous structures lead to “Convergent Evolution” � Forelimbs of vertebrates (human versus horse) � Wings of birds and bats (arm bones versus hand bones)

Molecular Record � � Due to the mechanism of evolution, one should observe the more distant the relatives, the less similar their genomes will be Conversely, the closer the evolutionary relatives, the more similar their genomes will be In reality, the genetic evidence supports the previous statements, which in turn further strengthens theory of evolution This same pattern of divergence as the evolutionary relatives become less similar can also be seen at the level of the protein

Molecular Record

Evolution’s Critics � Arguments advanced by Darwin’s Critics: � 1. Evolution is not solidly demonstrated …. Evolution is just a theory � 2. There are no fossil intermediates (in the 1800’s) � 3. The Intelligent Design argument - “The organs of living creatures are too complex for a random process to have produced. ” � 4. Evolution violates the second law of thermodynamics – “tendency of the universe toward disorder”; what the law really states: “disorder increases in a closed system”

Evolution’s Critics � 5. Proteins are too improbable � 6. Natural Selection does not imply evolution � 7. Life could not have evolved in water

Population Genetics � � If the allele frequencies of a population are not changing, then the population is not evolving … this is “Hardy-Weinberg equilibrium” There are many factors that can propel a population out of Hardy-Weinberg equilibrium: � 1. change in size of the population � 2. immigration � 3. genetic mutations � 4. monogamous nonrandom matings

Population Genetics � � In order for a species to remain extant genetic diversity is very important There are several factors that enhance genetic diversity: � 1. many individuals of a species � 2. many populations of a species � 3. immigration and emigration � 4. constant reproduction � 5. minimal inbreeding

Conservation Genetics � � � Conservation geneticists use their knowledge and understanding of DNA to increase genetic diversity through breeding They artificially control/manipulate which individuals are able to breed in order to encourage an increase in genetic diversity As the endangered species total number and variation in the gene pool increase, the likelihood the species will survive increases

More Evolution Terms � � � Genetic Drift – random fluctuations in allele frequencies in a small population over time Founder Effect – the effect by which rare alleles and combinations of alleles may be enhanced in new populations ( an island) Bottleneck Effect – a catastrophic event that greatly reduces the size of a population thereby greatly reducing the genetic variation of the population

Types of Natural Selection

Types of Natural Selection � � � Stabilizing Selection – extreme phenotypes are eliminated (baby birth weight) Disruptive Selection – the common intermediate phenotype is eliminated and the extreme phenotypes are preserved (finch beaks are large and small) Directional Selection – one extreme phenotype is eliminated (minimal presence of phototropism in fruit flies)

Sickle Cell Anemia “Stabilizing Selection” � � � Blood clotting disorder found in Americans of Central African decent and in those people still residing in Central Africa It is a painful disorder that reduces the bloods ability to carry oxygen due to the shape of the hemoglobin; the sickle shape of the hemoglobin causes it to get caught in the tiny capillaries of a person’s circulatory system thereby causing extreme discomfort; Someone with the disorder usually has a shortened lifespan It does serve a purpose, especially in Central Africa: those people with it are much less susceptible to Malaria, which is often deadly Homozygotes for sickle cell anemia die early in life, Heterozygotes are resistant to Malaria, Homozygotes that do not have sickle cell anemia will die if they contract Malaria

Environment versus Evolution � � � If there is no change in the environment, then there is no need for physical changes in a species However, the only thing that stays the same is that the environment changes The abiotic changes in the environment make it more likely for species mutations to be demonstrated in the population

The Peppered Moth Example

What Makes A Species � � A species is defined as those individuals that can mate with each other and produce offspring that are reproductively capable themselves Speciation is the process by which new species develop from already existing species How does speciation occur? (Darwin’s Finches) Speciation occurs via “Isolating Mechanisms”

Isolating Mechanisms