Evolution The Nature of

Changeand Variation

What is Evolution?

Simply… a change in living organisms over time

Why study evolution? Evolutionary concepts provide a

solid foundation to much of modern biology

- you can’t fully understand current trends in biology or you will have difficulty understanding evolution

Evolution involves inheritable changes in

organisms through time is fundamental to biology and paleontology

Paleontology is the study of life history as revealed by fossils

Evolution is a unifying theory like plate tectonic theory

that explains an otherwise encyclopedic collection of facts

Evolution provides a framework for discussion of life history

Why Study Evolution?

Many people have a poor understanding of the theory of evolution they hold a number of misconceptions, which include:

evolution proceeds or advances strictly by chance

nothing less than fully developed structures – such as eyes are of any use

there are no transitional fossils – so-called missing links– connecting ancestors and descendants

humans evolved from monkeys – so monkeys should no longer exist

Misconceptions about Evolution

Evolutionary theory is the framework tying together all of biology.

It explains similarities and differences between organisms, fossils, biogeography, drug resistance, relative virulence of parasites, and much more. 

What is a scientific “theory”?

Theories are structures of ideas that explain and interpret facts. 

In the early days...

Prior to 1760 -people believed organisms were fixed- that is they didn’t change

1744-1829 – Jean Baptiste Lamarck Evolution through the inheritance of

acquired characteristics Traits acquired during an organism’s

life could be passed on to their offspring

Giraffes long necks explained by repeated stretching

hypothesis rejected

According to Lamarck’s theory of inheritance of acquired characteristics

Lamarck’s Giraffes

– ancestral short-necked giraffes

– stretched their necks

– to reach leaves high on trees.

– Their offspring were born

– with longer necks

Lamark’s theory was not totally disproved until decades later with the discovery that genes cannot be

altered by any effort by an organism during its lifetime

Lamarck’s Theory

Basic Types of Evolution

Macroevolution = speciation – the formation of new species. The change in species over long periods of time. Not immediately observable.

Microevolution = changes in genes/alleles within a population.

Can be observed in a human lifetime.

Macroevolution/Microevolution

Macroevolution1. Large-scale

changes in gene frequencies

2. Occurs over a longer (geological) time period

3. Occurs at or above the level of species in separated gene pools

4. Consists of extended

microevolution

Microevolution1. Small-scale

changes in gene frequencies

2. Occurs over a few generations

3. Occurs within a species or population in same gene pool

4. Refers to smaller

evolutionary changes

Macroevolution/Microevolution

Macroevolution5. Has not been directly

observed6. Evidence based

on remnants of the

past 7. More

controversial 8. Example: Birds

from reptiles

Microevolution5. Observable

6. Evidence produced

by experimentation

7. Less controversial

8. Example: Bacterial

resistance to antibiotics

If all existing organisms descended with modification from ancestors that lived during the past,

all life forms should have fundamental similarities: all living things consist mainly of carbon,

nitrogen hydrogen and oxygen their chromosomes consist of DNA all cells synthesize proteins

in essentially the same way

Biological Evidence Supporting Evolution

Biochemistry provides evidence for evolutionary relationships

Blood proteins are similar among all mammals Humans’ blood chemistry is related

most closely to the great apes then to Old World monkeys then New World monkeys then lower primates such as lemurs

Biochemical test support the idea that birds descended from reptiles

a conclusion supported by evidence in the fossil record

Evolutionary Relationships

Organisms in all populations possess heritable variations such as size, speed, agility, visual acuity, digestive enzymes, color, and so forth

Some variations are more favorable than others some have a competitive edge in acquiring resources and/or avoiding predators

Not all young survive to reproductive maturity Those with favorable variations are more likely to survive and pass on their favorable variations

Natural Selection—Main Points

In common nonscientific usage, natural selection is sometimes expressed

as “survival of the fittest”

“Survival of the Fittest”

This is misleading because natural selection is not simply a matter of survival - but involves differential rates

of survival and reproduction

One misconception about natural selection is that among animals only the biggest, strongest, and fastest are likely to survive These characteristics might provide an advantage

but natural selection may favor the smallest if resources are limited the most easily concealed those that adapt most readily to a new food source those having the ability to detoxify some substance and so on...

Not only Biggest, Strongest, Fastest

Darwin observed Galapagos finches showing variations in beak shape and size from island to island. He reasoned these differences made the finches better adapted to the food in their particular local environment.Each finch population had developed beaks which were suitable for that particular environment.

Phylogenic Tree

Phylogenic trees trace patterns of shared ancestry between lineages.

Each lineage has a part of its history that is unique to it alone and parts that are shared with other lineages.

Natural selection works on existing variation in a population

It could not account for the origin of variations Critics reasoned that should a variant trait

arise, it would blend with other traits and would be lost

The answer to these criticisms existed even then in the work of Gregor Mendel, but remained obscure until 1900

Limits of Natural Selection

Evidence of Change Fossil Record Embryology Molecular Biology-Amino Acids,

Nucleotides, DNA sequencing, mitochondrial DNA

Anatomy commonalities Various adaptations

EVIDENCE OF EVOLUTION

STRUCTURAL ADAPTATIONS MIMICRY CAMOUFLAGE

http://evolution.berkeley.edu/evolibrary/home.phphttp://science.howstuffworks.com/animal-camouflage2.htm

Fossil Record Fossils are a major source of

information about changes in life during the

distant past In general, fossils show that life has increased in diversity and complexity over time

Fossil Record

Interpretation of the distribution of fossils in the rock initially based on the principle of superposition

- in undisturbed rock layers, older fossils will be found lower in the rock than younger fossils

-radiometric dating confirms this

In general older life forms tend to be less complex

Periods of diversity are interrupted by mass extinctions – followed by new life forms Fossil Record is incomplete – estimated only 1

in 10,000 extinct species are represented – Why?

Embryology All vertebrate embryos have

Gill slits on sides of the throat Post anal tail

The fact that organisms without gills, or tails have them as embryos is taken as evidence of a common ancestry with organisms that had both

Which is the fish, rabbit, human, chicken, tortoise?

Comparative Anatomy

Similarities in structure between organisms was used

to determine evolutionary relationships

Other Proof From Anatomy

Vestigial structures – structures that are greatly reduced with little or no function

- they are thought to be left over from ancestors

Pelvis and leg bones in snakes Reduced toe in horse Appendix in human Coccyx (tail bone) in humans

Vestigial Structures

Comparative Anatomy

Analogous Structures Similar function but

different structure - Insect’s wing, Bird’s

wing and Bats wings – all allow flight, but

are structurally different

Eyes of Mollusks and Vertebrates – both allow sight, but are different in structure

Comparative Anatomy

Homologous Structures Have a similar structure but different

function The forelimbs of vertebrate animals all

have the same structural design, but they have different functions

This similarity of structure shows a common ancestry

Homologous Structures

Analogous structures

Molecular Biology Comparisons of the sequences of

amino acids in proteins or nucleotides in DNA

can show the relationships between organisms

the number of differences in the sequences of amino acids or nucleotides indicates how closely related two organisms are

Hemoglobin Comparison

Species AA differences from humans

Gorilla 1Rhesus Monkey 8Mouse 27Chicken 45Frog 67

Hemoglobin Cladogram

Cladogram (family tree) created from a fossil record

Bird Evolutionary Tree

Phylogenic Trees and Cladograms are also created using comparative DNA sequences.

If the DNA is very similar to each other, it means they share a fairly recent common ancestor.

During his voyage, Darwin observed fossil mammals in South America that are similar to yet different from present day animals.

Ex. Llamas, sloths, and armadillos. The finches and giant tortoises lining on the Galapagos Islands vary from South America, even though they differ in subtle ways.

These observations convinced Darwin that organisms descended with modification from ancestors that lived during the past which was his central claim of the theory of evolution.

Darwin Developed the Theory

Charles DarwinAlfred Wallace

Descent with modification. The Origin of Species. 1859

Species were not created in their present forms but evolved from an ancestral species.

Natural selection, the mechanism by which change occurs (Explanation

of how evolution occurs).

Darwin and Alfred Russel Wallace (1823-

1913) read John Malthus’ book and came to the same conclusion,

that a natural process was selecting only a few individuals for

survival Darwin’s and Wallace’s idea

called natural selection was presented simultaneously in 1859

Darwin and Wallace