DESCENT WITH MODIFICATION:A DARWINIAN VIEW OF LIFE

What is Evolution? The change in gene frequencies in a population over time

What is evolution? Organism evolution means changes in populations,

species, or groups of species.

It occurs because:1. Populations vary by the frequency of heritable

traits that appear from one generation to the next.2. These traits are represented by alleles for genes

that modify morphology (form/structure), physiology, or behavior.

3. There is a struggle for survival and most organisms perish. Only those that survive pass their genes on.

Can individuals Evolve?

NO. Individuals can BE different and can survive and pass those genes on or be killed and not.

For an organism to change itself to suit its environment it would need to change the genes (DNA) inside every cell of it’s body.

Most importantly, they would need to change the DNA in their gametes- so the “change” could be passed on to the next generation.

Some individuals are better suited for their environment. They leave more offspring. Over generations, the genetic composition of a population reflects more of their “beneficial” genes.

Historical Context of Evolutionary TheoryParadigm shift from organisms are STATIC to the idea that organisms can CHANGE FORM.

Plato (427-347 B.C.) Two worlds: real/ideal world that is eternal and world of imperfection we perceive through senses. Living things were created in their perfect, static form by the gods.

Aristotle (384-322 B.C.) “scale of nature” all living forms could be arranged on. Each form assigned a rung, all rungs were taken.

LADDER OF LIFE

Aristotle’s "steps of nature," or the "hierarchy of nature”…

Tree of Life

instead of a ladder or hierarchy…

tips of branches

Natural theology

A philosophy dedicated to discovering the Creator’s plan by studying nature- the earth and it’s inhabitants.

1. Adapations were evidence that the Creator had designed each and every species for a particular purpose.

2. Classifying species was a major objective.

Carolus Linnaeus

(1707-1778) Specialized in taxonomy- naming and

classifying the diverse forms of life. Developed binomial nomenclature- a

two part naming system. Developed a system of grouping similar

species into a hierarchy of increasingly general categories. (species- genus- family)

He saw no evolutionary relationships in his groupings.

Georges Cuvier (1769-1832)

Largely developed paleontology- the study of fossils.

Opposed to the idea of evolution. Advocated catastrophism, the principle that

events in the past occurred suddenly and by different mechanisms than those occurring today.

Each boundary between strata corresponded to a catastrophe (drought, flood, super volcano) destroyed many of the local species.

Area repopulated by immigration.

Formation of sedimentary rock and deposition of fossils from different time periods

Fathers of Modern GeologyHutton & Lyell

1795 James Hutton, Scottish geologistExplained Earth’s geologic features by the theory of Gradualism: Speciation occurs gradually, profound change is the cumulative product of slow but continuous processes.

Charles Lyell (1797-1875) geologist incorporated gradualism into the

theory of Uniformitarianism: Geologic processes have not changed throughout Earth’s history (ie. forces that build and erode mountains occur at a steady rate) thus Earth is much older than previously believed.

Strata of sedimentary rock at the Grand Canyon

IMPORTANT CONCLUSIONS: Earth must be very old much older than six

thousand years (it is 4.5 billion years old) Very slow and subtle processes persisting over a

long period of time can add up to substantial change.

Slow but significant changes in environments caused slow but significant changes in species over “geologic time.”

By the end of the 18th century several naturalists, including Darwin’s grandfather Erasmus Darwin, suggested that life had evolved as environments changed.

No one had suggested a mechanism.

The Inheritance of Acquired CharacteristicsJean Baptiste de Lamarck proposed the first explanation that was widely accepted for years.

Three parts:1) Use and disuse described how body parts of organisms can

develop with increased usage, while unused parts weaken. Correct.

2) Inheritance of acquired characteristics described how body features acquired during the lifetime of an organism (such as muscle bulk) could be passed on to offspring. Incorrect.

3) Natural transformation of species described how organisms produced offspring with changes, transforming each generation into a slightly different form that is more complex. Species did not become extinct nor did they split and change into two or more species. Incorrect.

The giraffe

Short neck. Food scarce. Stretch neck. Eat. Have a slightly longer neck. Have offspring with slightly longer

neck. Repeat. Inheritance of Acquired

Characteristics or Lamarckism

Descent with Modification via Natural Selection by DARWIN Charles Darwin 1809-1882

Med school dropout BA Natural Theology Captain Fitzroy- HMS

Beagle - 5 years of travel UNPAID

Galapagos, islands of relatively recent volcanic origin, 900 km west of SA coast.

Gathered mountains of evidence

Waited 20 years to write and publish a groundbreaking book.

Alfred Russell Wallace(1823-1913)

Presented a paper with identical ideas as Darwin on July 1, 1858 at the Linnaean Society meetingWas a botanist who came up with virtually the same concept of natural selection more or less independently through his studies on the Malay archipelago. Darwin panicked because he was not ready with his book yet!

Journey of the H.M.S. Beagle

The historical context of Darwin’s life and ideas.

Tropical Rainforest of South America

Darwin’s Field Research S.American flora/fauna are distinct from European

flora/fauna• S. American temperate species were more closely

related to S. American tropical species than European temperate species

• S. American fossils were distinctly S. American

Darwin’s Field Research Most animal species on Galapagos unique to those

islands, but resemble S. American continental species Darwin’s Finches 13 types

some unique to individual island others found on two or more islands close together

• Darwin proposed• new species could arise from an ancestral population by

gradually accumulating adaptations to a different environment.

• Theory of natural selection as the mechanism of adaptive evolution

On the Origin of SpeciesBy Means of Natural Selection November 24, 1859

Darwins’s groundbreaking book explained what had once seemed a bewildering array of unrelated facts.

He focused on:• Diversity of organisms• Similarities & differences

• Geographic distribution• Adaptations to surrounding

environments

Main Ideas of Natural Selection1) Overproduction of

offspring… populations posses an enormous reproductive potential.

ex. Darwin calculated that two elephants would produce a population of 19 million individuals after 750 years if all offspring survived to reproductive maturity and fostered their normal number of offspring.

Main Ideas of Natural Selection2) Members of a population compete for survival.

Population sizes remain stable- populations

generally fluctuate around a constant size. Resources are limited. Resources such as

food, water, light don’t increase as populations grow larger.

Eventually, the needs of a growing population will exceed the available resources.

As a result, individuals must compete for resources.

Main Ideas of Natural Selection3) Genetic variability exists among

individuals in a population. Most traits reveal considerable

variety in their form.

Main Ideas of Natural Selection

4) Some individuals will be better suited for their environment.

Only the individuals most fit to their environment survive to breed.

Individuals with traits best adapted for survival in the environment are able to out-compete other individuals for resources.

Main Ideas of Natural Selection5) Individuals with the better

adaptations survive and leave offspring who inherit the traits of their parents.

In turn, the best adapted of these offspring leave the most offspring.

Over time, traits best adapted for survival in the environment and the alleles that generate them accumulate in the population.Evolution occurs as advantageous traits accumulate.

Key Points of Natural Selection

1. Populations (groups of interbreeding individuals belonging to a particular species and sharing a common geographic area) are the smallest unit that can evolve. Evolution is measurable over successive generations.

2. Natural selection acts only on heritable variations/phenotypes. (not acquired ones)

3. Natural selection is situational as environmental factors vary from place to place and from time to time. An adaptation in one situation may be useless or even detrimental in another situation.

Natural selection is differential success in reproduction that results from the interaction between individuals that vary in heritable traits and their environment

Summary1. Theory - an accepted hypothesis that

has been tested over and over again without yet being disproved

2. Definition - Evolution is the change in the overall genetic makeup of a population over time

3. Three Basic Components1. Individuals cannot evolve.  Populations

evolve.2. Natural selection is the mechanism of

evolution.3. Evolution occurs situationally (NOT GOAL

ORIENTED).

Artificial Selection

• Humans make breeding choices among livestock, crops, dogs, horses, etc.

ORGANIZE YOUR THOUGHTS!EVIDENCE FOR EVOLUTION

1. Direct Observations2. The Fossil Record3. Homology4. Biogeography

EVIDENCE FOR EVOLUTIONDirect observation

1. Historical examples that support the theory of natural selection

1. Pesticide resistance2. Antibiotic resistance3. HIV4. Sickle Cell Anemia- Malaria

Evolution of insecticide resistance in insect populations

Evolution of drug resistance in HIV

EVIDENCE FOR EVOLUTIONThe Fossil Record

2. Paleontology provides fossils that reveal the prehistoric existence of extinct species. As a result, changes in species and the formation of new species can be studied.

Fossil deposits are often among sediment layers.

Law of superposition states that the deepest layer of earth contains the oldest specimens.

Fossil Record

The fossil record refers to the order in which fossils appear within layers of rock that mark the passing of geologic time.

PATTERNS OF EVOLUTIONHomology3. Comparative anatomy describes two kinds of

structures that contribute to the identification of evolutionary relationships among species. Compares external morphology and internal anatomy

• Homologous structures: have different functions and may look different but may resemble one another in different species because they have evolved from a common ancestor.

• Divergent Evolution: two or more species originate from a common ancestor.

Morphology

Homologous structures: anatomical signs of descent with modification

EVIDENCE FOR EVOLUTION Embryology is the study of

embryos and their development. Reveals similar stages in

development (ontogeny) among related species.

The similarities help establish evolutionary relationships (phylogeny).

Ontogenetic Homology

The human embryo has gills, a post-anal tail, webbing between the toes & fingers, & spends its entire time floating and developing in amniotic fluid has similar salt concentration as ocean water

Figure 22.15

Pharyngealpouches

Post-analtail

Chick embryo Human embryo

EVIDENCE FOR EVOLUTION

Vestigial organs: organs with no apparent function or purpose imply evolutionary relationships to primitive ancestors.

May still be around as an evolutionary relic.

The structure served a purpose in an ancient ancestor but no longer does.

Example: pelvic girdle, hind leg bones in whales

A transitional fossil linking past and present

EVIDENCE FOR EVOLUTION Molecular Biology examines the

nucleotide and amino acid sequences of DNA and proteins from different species.

Closely related species share higher percentages of sequences than distantly related species.

All living things share the same genetic code.

Favors evolution of different species through modification of ancestral genetic information.

For example, more than 98% of the nucleotide sequences in humans and chimpanzees are identical.

Molecular Data and the Evolutionary Relationships of Vertebrates

EVIDENCE FOR EVOLUTION4.Biogeography

• Convergent Evolution• When two unrelated species that

share similar traits arise not from a common ancestor but because each species has independently adapted to similar ecological conditions or lifestyles.

EVIDENCE FOR EVOLUTION

Analogous Structures

body parts that resemble one another in different species, not because they have evolved from a common ancestor

they evolved these similar adaptations independently because they evolved in similar environments with the same selection pressures.

Similar solutions to similar problems

EVIDENCE FOR EVOLUTION

4. Biogeography: geographic distribution of species.

Has revealed that unrelated species in different regions of the world look alike when found in similar environments.

Endemic species are found at that certain geographic location and nowhere else

Continental Drift Theory the breakup of Pangaea can explain the similarity of species on continents that are similar today.

PATTERNS OF EVOLUTION Parallel

Evolution Two related

species making similar evolutionary changes after their divergence.

Marsupial and Placental mammals

PATTERNS OF EVOLUTION Co-evolution

Tit-for-tat evolution of one species in response to new adaptation that appears in another species

Pollinators and flowering plants

Natural Selection in Action

Camouflage

Figure 22.11

(a) A flower mantidin Malaysia

(b) A stick mantidin Africa

• If an environment changes over time

Natural selection may result in adaptation to these new conditions

Natural Selection in Action

Eye spots

Natural Selection in Action

Counter Shading

Natural Selection in Action

Disruptive Coloration

Natural Selection in Action

Mimicry

Monarch or Viceroy Butterfly

Summary Evolution is change

in species over time Heritable variations

exist within a population

These variations can result in differential reproductive success

Over generations this can result in changes in the genetic composition of the population.