Principles of Evolution

BIO 101

Life Science

Dr. D. L. Daley


Evolution: A Definition

Change in a line of descent overtime.


Change over time in the characteristics of populations

Evolution in Action

Peppered moth (Biston betularia ) - England

Prior to mid-19th century - most moths were light colored - speckled light-gray wings which were hard to see against lichen covered trees

Dark wing moths were very rare

Evolution in Action

Howeve ras the century progressed the soot of the industrial revolution darkened the habitat of the moth.

Lichens on the trunks of trees are sensitive to pollution - died.

Light wing moths were now more visible to birds that preyed on them.

Evolution in Action

However some moths were dark and thus were not easily visible.

As pollution increased so did dark moths

In1886 - 98% of moths in some industrial areas were dark-winged

Thus light moths were eaten & dark ones survived

Evolution in Action

In1952 strict pollution controls went into effect - lichens on the trunks of trees made a come back (tree trunks thus are getting lighter over time)

As you might predict - the frequency of dark-wing moths is also declining

More recent research (Majerus,1998) suggests that bird predation may not be only one factor in the story of the peppered moth and that other factors such as migration and differential behavior help explain the rise and then fall in the dark form of the peppered moth

Camouflage in Moths



Evolution: Core Principles

Common Descent With Modification

Groups of living things can undergo modification in successive generations.

These changes can sometimes result in the formation of new species.

One species separating into two and these separating further

Videotape example

Evolution: Core Principles

Natural selection

The “fit” of an organism with its environment selects those traits that will be passed on with greater frequency to the next.

Redwood tree example

Why are redwood trees so tall?

Darwin’s Contribution

1.He developed existing ideas about descent with modification while providing a large body of evidence in support of them.

2.He was the first to perceive natural selection is the primary force behind evolution.

Note: Alfred Russel Wallace working separately, came to the same conclusion also in1858

Darwin’s Insights: After his Voyage

Started with Darwin’s collections of birds

He originally thought were blackbirds, wrens, warblers and finches

Actually separate species of finches.

Related to an ancestral species found on the mainland of South America

Thus members of the ancestral species had come by air to the Galapagos

Then fanning out to separate islands - they diverged over time into separate species

Darwin’s Finches





Modern Definition: Evolution

Any change in gene frequency in a population of organisms.

Evolution refers to what happens to populations (groups of interbreeding organisms) not entire species.

Gene Frequency

Refers to the proportion of each form of a gene at a given locus relative to the total number of genes at that locus in a group of organisms

Also called allele frequency


Blood type example!

Darwin and Wallace - Mechanism of Evolution

In1858 Charles Darwin and Alfred Wallace working separately - proposed a simple mechanism for evolution

Darwin was the first to put it in writing (1842) - not published

16years later he received a draft of a similar paper from Wallace

Thus he could not delay - Darwin submits a paper

Wallace sent his paper in also

Both presented their work to the Linnaean in London in 1858

Natural Selection

Some individuals are more successful than others in surviving and hence reproducing, owning to traits that give them a better “fit” with their environment

Thus the alleles of those who reproduce more will increase in frequency in a population.

Evidence for Evolution

Radiometric dating

The earth is old - 4.6 billion years

The placement of fossils

Looking at the same geologic layers worldwide, showed that the same general fossils are found

Also as you go up through new strata more complex organisms are found

Fossils: Archeopteryx






Evidence for Evolution

Comparative anatomy

Horse hooves and human hands despite outward differences are similar in the number and position of their bones

Homologous Structures






Functionless Structures Inherited from Ancestors

Evolution by natural selection - explains curious circumstances of vestigial structures that serve no purpose


Molar teeth in vampire bats that live on a diet of blood & thus do not chew their food

Pelvic bones in whales and certain snakes - these are vestigial and are clearly homologous to structures that are found in use by other vertebrates

Their continued existence - best explained as “evolutionary baggage”

Convergent Evolution and Analogous Structures

Some similarities in structure stem from convergent evolution - here natural selection causes nonhomologous structures that serve similar functions to resemble one another

Any example is that birds and insects both have wings - they however did not arise by modification of structure inherited from a common ancestor - rather natural selection favored flight in both groups and they evolved superficially similar structures - wings

Embryological Similarity Suggests Common Ancestry

In early developmental stages fish, turtles, chickens, mice and humans all develop tails and gill slits

As adults only fish retain gills and only fish, turtles and mice retain substantial tails


Ancestral vertebrates possessed genes that directed the development of gills and tails and all descendents still have those genes

In fish the genes for tails are active throughout development

In chickens and humans these genes are only active in early development

Modern Analyses Reveal Relatedness

A comparison of DNA of different organisms can reveal their relatedness

A powerful demonstration of relatedness emerges when molecular comparisons are made between organisms that have no anatomical features in common

Cytochromec is an example, this protein is found in all plants, animals and many single celled organisms - in all these organisms it performs the same function

The widespread presence of this protein is excellent evidence that these diverse organisms shared a common ancestor that had cytochrome c in its cells

Moreover, the more closely related the species the more similar is the exact sequence of the protein

Cytochromec between humans and mice only a 10% difference exists

Cytochromec between humans and corn the difference is about 33%

How Does Natural Selection Work?

Based on 4 postulates about population of organisms

1.Individual members of a population differ from one another in many respects

2.At least some of the differences among members are due to characteristics that may be passed from parent to offspring

3.In each generation, some individuals in population survive and reproduce successfully but others do not.

4.The fate of individuals is not determined entirely by luck. Instead, an individual’s likelihood of survival & reproduction depends upon its characteristics.  Thus individuals with advantageous traits survive longest and leave the most offspring - natural selection

Artificial Selection

One line of evidence supporting evolution by natural selection come from artificial selection.

In a few thousand years humans have produced radically different dogs by performing selective crosses

In fact if some of these dog breeds were found in the wild they would be considered separate species

Therefore natural selection could by an analogous process acting over millions of years and produce the spectrum of living organisms