Theory of EvolutionChapter 15

01.24.08 / 01.25.08

Definition

• Evolution is the process of change in the inherited characteristics within populations over generations such that new types of organisms develop from preexisting types.– “decent with modification”

or

• Evolution is the change in a population’s allele frequency across generations

Ideas of Darwin’s Time

• Scientific understanding of evolution began to develop in the 17th and 18th centuries as geologists and naturalists compared geologic processes and living and fossil organisms around the world.– uniformitarianism

Ideas of Darwin’s Time

• In the early 1700s, Carl Linnaeus developed a system for classifying animals by their similarities

• Linnaeus was motivated by his belief in Natural Theology

• “The flowers' leaves…serve as bridal beds which the Creator has so gloriously arranged, adorned with such noble bed curtains, and perfumed with so many soft scents that the bridegroom with his bride might there celebrate their nuptials with so much the greater solemnity.”

Ideas of Darwin’s Time

• Evolution (change over time) was accepted well before Darwin was even born– But, what caused it?

• Lamarck’s inheritance of acquired characteristics (1809)– Examples included:

• Webbed feet of birds• Long neck of giraffes

– This explanation was never widely accepted

Ideas of Darwin’s Time

• Evolutionary theory significantly related to:– Adam Smith’s capitalism (1776)

• Self-interest

• Invisible Hand

– Malthus’s view of overpopulation (1798)• Population increases exponentially, while

resources increase arithmetically

• Mass starvation is the consequence

Ideas of Darwin’s Time

Organic life beneath the shoreless wavesWas born and nurs'd in ocean's pearly caves;First forms minute, unseen by spheric glass,Move on the mud, or pierce the watery mass;These, as successive generations bloom,New powers acquire and larger limbs assume;Whence countless groups of vegetation spring,And breathing realms of fin and feet and wing.                 Erasmus Darwin The Temple of Nature, 1802

Darwin’s Ideas

• Darwin’s father was a physician, so Darwin needed a respectable job, too– He went to medical school, but dropped out

because surgery freaked him out– He then studied theology because being a

minister was a decent career for upper-class men with few other skills

– He eventually gave that up and asked his family for money to travel on the HMS Beagle

Darwin’ Ideas

• Darwin was raised in the religious tradition of Natural Theology

• His studies of the world made him question the goodness of God because he saw suffering and futility

• The death of his daughter in 1851 finalized his move toward agnosticism

Darwin’s Ideas

• During his 5-year trip on the Beagle (1831-1836), Darwin published a paper on geology, which made him a well-respected scientist

• In 1839, he wrote about natural selection, but he did not submit it for publication

• In 1858, Alfred Wallace wrote to Darwin asking him to read over a paper on natural selection

Darwin’s Ideas

• Darwin argued that:– descent with modification occurs– that all species descended from common ancestors, – that natural selection is the mechanism for evolution.

• Natural Selection– Organisms in a population adapt to their environment

as the proportion of individuals with genes for favorable traits increases.

– Those individuals that pass on more genes are considered to have greater fitness.

Darwin’s Ideas

• Natural Selection occurs through:– Overproduction do you see Malthus?

– Genetic variation

– Struggle to survive– Differential reproduction do you see Smith?

Evidence for Evolution

• Four main lines of evidence– Fossil record– Biogeography– Anatomy and embryology– Biological molecules

• Evolutionary descriptions often involve a combination of evidences

Video

• Time to watch a podcast: – “Evidence for Evolution”

Fossil Record

• The fossil record shows that the types and distribution of organisms on Earth have changed over time.

• Fossils of transitional species show evidence of descent with modification.– Note: Some scientists disagree with the term

transitional species

Biogeography

• Biogeography, the study of the locations of organisms around the world, provides evidence of descent with modification.– Most Australian mammals are marsupials– Wallace divided the world into 6

biogeographical realms• Note: His idea was developed before continental

drift

Anatomy & Embryology

• analogous structures are similar in function but have different evolutionary origins. – Think analogies, things that are different, but

have a functional similarity

• homologous structures have a common evolutionary origin.– homo means “same,” so these are structures

from the same origin

Anatomy & Embryology

• vestigial structures are parts that have no current function, but were used in an ancestor– The human tailbone

• Although this is used to hold muscles in place

– Whale pelvises– The human appendix was once thought to be

a vestigial structure, but is not thought to play an important role in healing from intestinal disease

Anatomy & Embryology

• Related species have very similar embryological processes

Biological Molecules

• Similarity in the subunit sequences of biological molecules such as RNA, DNA, and proteins indicates a common evolutionary history.– There is a lot of current debate around issues

of junk DNA

Developing Theory

• Modern scientists integrate Darwin’s theory with other advances in biological knowledge.

• Theories and hypotheses about evolution continue to be proposed and investigated.

Evolution in Action

• Ongoing examples of evolution among living organisms can be observed, recorded, and tested.

• In convergent evolution, organisms that are not closely related resemble each other because they have responded to similar environments.

Evolution in Action

• In divergent evolution, related populations become less similar as they respond to different environments.

• In adaptive radiation, a single group of organisms goes through divergent evolution in a new environment.– Darwin’s finches– Caribbean anoline lizards

Evolution in Action• Artificial selection is when humans choose to

change the traits of animals– Domesticated animals, such as various dog

breeds are examples• Artificial selection often causes health problems• Purebred dogs have more health problems than

mutts and certain breeds are known for certain problems

– In a similar irony, the concept of a “pure race” of humans is harmful to the gene pool

• Cystic Fibrosis is much more common in whites than blacks

• Sickle Cell is much more common in blacks than whites

Evolution in Action

• Coevolution is the process of two or more organisms affecting each other’s change– coevolution does not imply codependence– antibiotic resistance among bacteria is an

example– Based on the characteristics of a specific

flower in Madagascar, Darwin predicted the size and shape of a moth that was not discovered until 40 years later