Chapters 22-25Evolution

Evolution

The definition of Evolution is:

change over time

Biological Evolution is:

genetic change in population over time

process by which modern organisms have descended from ancient organisms (slow change over long time)• Even relatively quick evolution takes hundreds of thousands of years

History of Evolutionary TheoriesPlato (427-347 B.C.) 2 worlds – 1 perfect, 1 imperfect. No change in organisms

Aristotle (384-322 B.C.) Organisms placed on “ladder of complexity / perfection” (scala naturae) No change

Judeo-Christian culture tried to explain the Creator’s plan as observable, natural phenomena – Natural Theology

History of Evolutionary TheoriesCarolus Linnaeus (1707-1832) Designed modern taxonomic system (binomial nomenclature)

From this system, we can (he didn’t) now infer evolutionary relationships between different groups

Geologists:Georges Cuvier

James Hutton

Charles Lyell

History of Evolutionary TheoriesGeorges Cuvier (1769-1832) helped develop Paleontology – study of fossils

Discovery of fossils (extinct species, similarities to modern species) put some doubt into Earth’s age and the origin of species

Cuvier explained differences in strata with “catastrophism” – floods, droughts, volcanoes, etc. changed local areas drastically over short periods of time

• Organisms did not change, just migrate

History of Evolutionary TheoriesJames Hutton (1726-1797) proposed that rocks, mountains, and valleys have been changed by water, wind, temperature, volcanoes, and other natural forces

He described the slow processes that shape Earth as “gradualism”

History of Evolutionary TheoriesCharles Lyell (1797-1875) – agreed with Hutton and said that scientists must always explain past events in terms of observable, PRESENT events and processes (“uniformitarianism” – what happens today happened yesterday)

They theorized Earth was much older than a few thousand (6,000) years, which didn’t set well in the traditional timeframe of Creationism

Age of the EarthWe now know Earth is approximately 4.5 billion years old

Darwin used the work of Hutton and Lyell as a basis for his theories of slow change over time. Darwin’s work was a biological duplicate of Hutton and Lyell’s works in geology.

Geologists study Earth’s rocksFossils are preserved remains of ancient organisms

As fossils are found that don’t resemble organisms today, evidence increases that Earth has changed and that organisms have changed with it

Biologists and geologists date Earth’s past with the help of rocks

Geological Time ScaleRELATIVE DATING

Technique used to determine age of fossils relative to other fossils in different strata

This technique is VERY approximate

Geological Time Scale

ABSOLUTE (RADIOMETRIC) DATING

Using radioactive elements in rock that decay at a steady rate to determine age

Decay measured in terms of HALF-LIFE

• Half-life – time required for half the radioactive atoms in a sample to decay

Radioactive Decay

During radioactive decay, the atoms of one element break down to form something else

6 protons

4 neutrons5 protons

4 neutrons

Lose a proton

Rocks contain radioactive elements, each having a different half-life

EXAMPLES:

Uranium-238 Lead-206 HL = 4.5 B yrs

Potassium-40 Argon-40 HL = 1.3 B yrs

Carbon-14 Nitrogen-14HL = 5770 yrs

Scientists often date rocks using Potassium-40, which decays to form the stable element Argon-40

It has a half life of 1.3 billion years

This is used to date the oldest rocks on earth

K-40

Formed 1.3 B yrs

K-40 Ar-40 Ar-40

2.6 B yrs

Uranium and Potassium are useful for dating rocks

Carbon-14 is useful for dating things that were once alive such as wood, natural fiber, or cloth

C-14 is in the atmosphere; living things take it in their cells. After the organism dies, it doesn’t take in any more C-14. We can then compare the amounts of C-14 to N-14, knowing its half-life, to determine the age of the sample

Fossil Evidence

Found in Sedimentary rock: layers of sand, silt, and clay in streams, lakes, rivers, and seas form rock that may have trapped living organisms

Fossil records – Show change over time. Some time frames are missing, but will show change of climate and geography.

Ex: Shark teeth in Utah

How can this be?

Jean Baptiste de Lamarck (1744-1829)

He also recognized that organisms were adapted to their environments and that they change

He relied on three ideas:

1. A desire to change (innate drive for perfection)

2. Use and disuse (Giraffe’s necks and vestigial organs)

3. Inheritance of acquired characteristics

Darwin’s Dilemma

Set sail around the world in 1831 on HMS Beagle on a 5 year voyage

He had prior knowledge of geology (Lyell was a good friend) and agriculture that helped influence the development of his theory

Anchored all along the way and took samples from each place

Darwin’s Dilemma

He collected and studied beetles from Brazil, birds from Chile, and iguanas, tortoises, and finches from the Galápagos Islands

He noticed similarities between mainland (Ecuador) and Galapagos finches

Later, he noticed differences in beak size among finches from different islands in the Galapagos

Darwin’s Dilemma

Thomas Malthus – wrote paper on population growth in Great Britain

Population grows exponentially

Limiting factors on growth (carrying capacity)

• Food

• Area

• Resources

Darwin’s DilemmaDarwin applied Malthus’, Hutton’s, and Lyell’s work to species’ ability to change, and called the mechanism Natural Selection

Nat.Sel.: Process by which organisms with favorable variations survive and produce more offspring than less well-adapted organisms

He was sure Nat.Sel. was true, but he feared public ridicule. So, he kept his ideas to himself

Darwin’s DilemmaAlfred Russel Wallace (1823-1913), working independently, came to the same conclusions as Darwin

He sent a manuscript to Darwin, basically for proofreading

“I never saw a more striking coincidence… so all my originality, whatever it may amount to, will be smashed.” – Charles Darwin

Letter to Charles Lyell, June 18, 1858

Darwin quickly abridged and published his work “On the Origin of Species”

Darwin’s Natural SelectionErnst Mayr, an evolutionary biologist, has dissected the logic of Darwin’s theory into three inferences based on five observations (Pg. 435)

Observations:

Tremendous fecundity

Stable populations sizes

Limited environmental resources

Variation among individuals

Heritability of some of this variation.

Darwin’s Natural SelectionObservation #1: All species have such great potential fertility that their population size would increase exponentially if all individuals that are born reproduced successfully.

Darwin’s Natural SelectionObservation #2: Populations tend to remain stable in size,except for seasonal fluctuations.

Observation #3: Environmental resources are limited.

Darwin’s Natural SelectionInference #1: Production of more individuals than the environment can support leads to a struggle for existence among the individuals of a population, with only a fraction of the offspring surviving each generation.

Darwin’s Natural SelectionObservation #4: Individuals of a population vary extensively in their characteristics; no two individuals are exactly alike.

Observation #5: Much of this variation is heritable.

Darwin’s Natural Selection

Inference #2: Survival in the struggle for existence is not random, but depends in part on the hereditary constitution of the individuals.

Those individuals whose inherited characteristics best fit them to their environment are likely to leave more offspring than less fit individuals.

Darwin’s Natural Selection

Inference #3: This unequal ability of individuals to survive and reproduce will lead to a gradual change in a population, with favorable characteristics accumulating over the generations.

Evidence in Living Organisms

Comparative embryology:

All vertebrate embryos look similar to one another in early development, with the development of a tail and gill arches

• Ernst Haeckel made early drawings – later exposed as frauds.

• Gave fuel to anti-evolutionists

Evidence in Living Organisms

Comparative embryology:

These anatomical similarities indicate similar genetics are at work

Become more dissimilar as they grow

• Cell specialization and differentiation

Common ancestor?

Evidence in Living Organisms

Evidence in Living Organisms

Comparative anatomy:

Homologous Structures

Analogous Structures

Vestigial Organs

Evidence in Living Organisms

Homologous Structures – structures that are similar in anatomy, but may serve very different functions

Ex: cat, whale, and human forearm

Homologous Structures

FlyingFlying SwimmingSwimming RunningRunning GraspingGrasping

Evidence in Living Organisms

Analogous Structures – structures that serve similar functions, but have evolved independently of each other

NotNot homologous; homologous;notnot analogous analogous Homologous;Homologous;

notnot analogous analogous

NotNot homologous; homologous;analogousanalogous

Homologous; Homologous; analogousanalogous

Evidence in Living Organisms.

Vestigial organs – organs that have little or no purpose in the organism; may become smaller or even disappear

Ex: Tailbone or appendix in humans

Ex: Tiny leg bones in snakes (boas and pythons) thought to come from 4 legged ancestor

Evidence in Living Organisms

Comparative biochemistry and molecular biology:

All cells have DNA, RNA, ribosomes, the same 20 amino acids and use ATP to do work

Similarities in biochemistry indicate relationship

Evidence in Living Organisms

Cytochrome c is a highly conserved respiratory protein containing 104 amino acids in humans

Evidence in Living Organisms

Amino acid differences of hemoglobin between species