Evolution Genetic change in population or species over generations.

Look at us now!!! Put some clothes on!

Theories of Evolution I. Lamarck’s Explanation: –French scientist ( ) –Proposed that similar species descended from a common ancestor (fossil records) –He hypothesized that acquired traits were passed on to offspring.

Acquired Trait It’s not determined by genes! Instead, it arises during an organism’s lifetime as a result of the organism’s experience or behavior. –Ex: 1. webbed foot on water birds resulted from repeated stretching of the membrane between the toes – 2. tails – if you don’t use it you loose it!

Thomas Malthus –Said, “much of human suffering – disease, famine, homelessness and war was the inescapable consequence of the human populations potential to grow much faster than the rate at which supplies of food and other resources could be produced –Resources couldn’t keep up with the increase in population this kept the population number down.

What were some of Darwin’s observations… 1. OVER PRODUCTION OF OFFSPRING all species tend to produce excessive numbers of offspring 2. HERITABLE VARIATIONS – individuals of a population vary extensively in their characteristics and that many are inherited 3. LIMITED NATURAL RESOURCES – environmental resources are limited

EVOLUTION and NATURAL SELECTION is NOT the same thing!! Evolution = genetic change Natural Selection = over production, limited natural resources and heritable variation influence a gradual change in the population!!

Charles Lyell (Scottish Geologist) Darwin was strongly influenced by his book Principles of Geology Gradual forces gradually change Earth’s surface and these forces are still operating today. Because of Lyell, Darwin believed that slow natural processes such as growth of mountains due t o earthquakes could account for the presence of marine fossils on the top of mountains! Natural catastrophes very important in evolution

Last one! Alfred Wallace: –Had theory IDENTICAL to Darwin! –Caused Darwin to publish “Origin of Species” by means of natural selection!!!

Beginning of Modern Evolutionary Theory II. Charles Darwin ( ) & Alfred Wallace ( ) –“natural selection”-hypothesis that organisms best suited to their environment reproduced more successfully than other organisms –Darwin & Wallace announced their hypotheses at the same time –Darwin’s name became more associated with evolution  The Origin of Species published

Darwin’s Voyage on the Beagle Sailed in 1831 for five years Collected specimens and kept careful records of his observations Sailed to South America (Galapagos Islands) and the South Pacific

Darwin’s Findings 1. returned to England in October collected 13 similar but separate species of finches. 3. Each finch species had a distinctive bill for specialized food source. Implied that the finches shared a recent common ancestor

Darwin’s Finches

Darwin’s Findings

A GRUB!!!!!!! !

Darwin’s Theories TWO THEORIES; –1. DESCENT WITH MODIFICATION – The newer forms appearing in the fossil record are actually the modified descendants of older species Organisms similar to each other come from a recent common ancestor, organisms that are more dissimilar such as finches and armadillos share a more remote ancestor

Continue… 2. MODIFICATION BY NATURAL SELECTION – states HOW evolution occurs. –Organisms having traits that make them better suited for survival tend to leave more offspring than organisms with fewer beneficial traits. Darwin called the different degrees of successful reproduction among organisms in a population NATURAL SELECTION

Evidence to support Darwin’s theory: Biogeography – the geographic distribution of species, first suggested to Darwin that organisms evolve from common ancestors Comparative Anatomy – the study of the body structures in different organisms, anatomical similarities gives evidence of a common ancestor

Continue… Homologous structures – structures that are similar in different species of common ancestry but have different functions Comparative embryology – closely related organisms often have similar stages in their embryonic development Fossils – imprints or remnants of organisms that lived in the past

Biogeography Biogeography – is the study of the geographical distribution of fossils and of living organisms. –A comparison of recently formed fossil types with types of living organisms in the same geographic area shows that new organisms arise in areas where similar forms already lived. Ex: armadillos in North & South America where glyptodonts lived in the past.

Armadillos

Glyptodonts

Evidence of Evolution 1. HOMOLOGOUS STRUCTURES: similar features that originated in a shared ancestor –Similar in structure BUT differ in function!! –Ex: penguin, bat, alligator, & human (all derive from the same embryological structures) –These examples i.e. share a fairly recent common ancestor

Homologous Structures

Continue… 2. ANALOGOUS STRUCTURES: Similar functions BUT differ in structure and embryological development –Ex: wings of a hummingbird and humming moth – both can hover to feed

Analogous Structures

Continue… 3. Vestigial Structure: Features that were useful to an ancestor, but they are not useful to the modern organism that has them. –Ex: tailbone in humans, appendix, some snakes have tiny pelvic bones and limb bones, some whales have pelvic bones along with four chambered stomach like a cow!

Vestigial Structures

Continue… 4. Similarities in Embryology –Ex: all vertebrate embryos are similar, but those similarities fade as development proceeds – evidence that indicates that vertebrates share a common ancestor

Vertebrate Embryos

Continue… 5. Similarities in Macromolecules: The more similar homologous proteins are in different species, the more closely related the species are thought to be. –Ex: the amino acid sequence in human hemoglobin and gorilla hemoglobin differ by ONE amino acid –While the Hb of humans and frogs differ by 67 amino acids!!

What’s natural selection? A mechanism of evolution that allows for differential (unequal) success in reproduction Examples: –Finches – dry years  large beaks (stronger) –Finches – wet years  small beaks –Insecticides  evol. Of hundreds of species

WAIT!!!!! What do you think of this?? Oh boy!

Let’s sum it up! SURVIVAL OF THE FITTEST! –Those whose characteristics adapt them best to the environment are most likely to survive and reproduce!! –Favored traits will be seen more and more while unfavored ones will be seen less and less in ensuing generations –EVOLUTION IS MEASURED IN A POPULATION NOT IN ONE INDIVIDUAL!

Patterns of Evolution 1. Coevolution: the change of two or more species in close association with each other is called coevolution –Predators and their prey sometimes co-evolve Ex: “tropical region” bats feed on nectar –Bats have slender muzzle and long tongue that help them to feed,flowers are light in color which helps bats to see them at night and have a fruity odor that is attractive to the bats.

Tropical Bats!

Baby Bats!!

CLOSE UP!!!! COOL!

Flowers with Nectar!

Continue… 2. Convergent Evolution: occurs when the environment selects similar phenotypes, even though the ancestral types were quite different from each other. –Analogous structures, such as similar fins in very different animals, are associated with convergent evolution Ex: sharks and porpoises

Porpoises

Sharks

Continue… 3. Divergent Evolution: two or more related populations or species become more and more dissimilar. Divergence is nearly always a response to differing habitats and can result in new species –A) adaptive radiation: many related species evolve from a single ancestral species ex: Galapagos finches –B) artificial selection: all domestic dogs are the same species “Canis familiaris”

Darwin’s ideas are supported by ARTIFICIAL SELECTION Artificial Selection –The selective breeding of desired traits that in fact modify species. Whoa nelly!!! Ex. Domestic dogs, cats, and plants –Broccoli, caulif., cabbage, brussel sprouts,

Canis familiaris !

So Darwin reasoned that if.. So much change could be achieved in a relatively short period of time by artificial selection, then over millions of years and hundreds of thousands of generations, natural selection should be able to modify species considerable. –YEAH BOY, UH-HUH

POPULATION GENETICS Populations  a group of individuals of the same species, living in the same place at the same time Populations are the smallest unit that can evolve.

How can we measure evolution? As a change in the prevalence of certain traits in a population over several generations

Individuals of a population do NOT evolve AGAIN… Natural selection acts on individuals-their char. Affect their chances of survival and reproduction. Evolution is only apparent when a population is tracked over time

Darwin understood evol., but didn’t understand the genetic basis of a population change… Today we know: –Spontaneous mutations may produce new traits –Segregation & indep. Assort. Produce variations in gametes & thus in offspring –Genes are passed through gametes from parents to offspring

MODERN SYNTHESIS Theory developed in the 1940’s Includes genetics and evolution!! POPULATIONS ARE THE UNITS OF EVOLUTION BASED ON NATURAL SELECTION

CONTINUE.. Modern synthesis deals with THE RELATIONSHIP BETWEEN POPULATIONS AND SPECIES SPECIES=group of organisms that can reproduce fertile offspring!

Where the species live matters! Species distributed over a geographic range –> have different gene pool THAN Species localized  due to water, islands, mountains etc.!!!

Studying evolution at the population level scientist focus on the GENE POOL GENE POOL IS THE SUM OF THE GENES IN A POLULATION! (It’s where all members of the next generation get their genes!)

MICROEVOLUTION When allele frequencies in a population change over generations, this is evolution at its smallest scale. (genes are represented by alleles) Ex: gene for the color of your eyes has many alleles – B,b)….

Let’s Review! 1. What is a GENE POOL? –Sum of genes in a population that will be passed on!!

What is microevolution? when allele frequency in a population change over generations this is evolution at its SMALLEST scale.

Remember! Sexual reproduction on its own does NOT cause microevolution Other agents must also act on the population! (environment)

There are several potential cause of microevolution: 1. Genetic Drift: - a) bottleneck effect - founder effect 2. Gene Flow 3. Mutation

Genetic Drift A change in the gene pool of a small population due to chance!

Genetic Drift Ex: Northern Elephant Seal (extinct)

The Bottleneck Effect Genetic drift resulting from an event that drastically reduces population size! Ex: hunting to the point of extinction!

The Bottleneck Effect *

Bottleneck Effect !

The Founder Effect Genetic drift that results from the colonization of a new location by a small number of individuals – small size, less representative of the gene pool.

Founder Effect Ex: Amish residents of Lancaster County, PA – Ellis-van Creveld Syndrome

Genetic Drift & Founder Effect Symptoms: short arms & legs, extra fingers, & in some cases heart defects.

Gene flow When fertile individuals move into or out of a population or when gametes are transferred between populations.

Gene Flow *

Gene flow *

Mutations A random change in an organism ’ s DNA that may create a new allele.

mutation HUH??

HARDY-WEINBERG EQUILIBRIUM Allele frequency with ONLY sexual reproduction involved! NO OUTSIDE AGENTS

VARIABLES p = dominant q = recessive 2pq = heterozygous p + q = 1 p 2 + 2pq + q 2 = 1

5 Conditions are required for Hardy-Weinberg Equilibrium 1. no mutations 2. no migration 3. very large population size

Continue… 4. random mating 5. NO NATURAL SELECTION OCCURS!

Hardy-Weinberg Equillibrium Conditions rarely met by a natural population Gives us a basis to compare nonevolving population vs. actual ones with gene pools that are changing!

Patterns of Selection Stabilizing Selection or Balancing Selection Disruptive Selection or Diversifying Selection Directional Selection

Stabilizing Selection Stabilizing selection is a type of natural selection that favors the average individuals in a population. This process selects against the extreme phenotypes and instead favors the majority of the population that is well adapted to the environment. Stabilizing selection is often shown on a graph as a modified bell curve that is narrower and taller than the norm.

Stabilizing Curve

Disruptive Selection Disruptive selection is a type of natural selection that selects against the average individual in a population. The make up of this type of population would show phenotypes of both extremes, but have very few individuals in the middle. Disruptive selection is the rarest of the three types of natural selection.

Directional Selection Directional selection is a type of natural selection that favors one extreme phenotype over the mean or other extreme. This phenomena is usually seen in environments that have changed over time. Changes in weather, climate, or food availability lead to directional selection.