Evolution

Life Science: Chapters 10, 11 and 12Biology: Chapters 14, 15 and 16

Early Naturalists

• Carolus Linnaeus – (1735) He proposed a system of organization for plants, animals and minerals based on their similarities

• George Buffon – (1749) He discussed ideas about relationships between species and sources of biological variation

• Jean Baptiste-Lamarck – (1809) presented evolution as occurring due to environmental change over long periods of time

Ideas that Led to a Theory

• Geologic Change – the common view was that the earth was only 6000 years old and that organisms did not change. Fossil evidence played a key role in this idea.– Catastrophism – Volcanoes, floods and other natural

disasters were the cause of extinction and the formation of all land forms.

– Gradualism – the idea that changes on Earth occurred by small steps over a long period of time

– Uniformitarianism – geologic processes add up over long periods of time to cause great change

Charles Darwin

Charles R. Darwin (1809-1882) was a British naturalist who was made famous by theorizing that processes such as natural selection and descent with modification played on species over time, leading to evolution. He published these theories and supporting evidence in his book, On the Origin of Species, in 1859.

Darwin collected evidence during his voyage around the world on the merchant vessel, the HMS Beagle. The trip lasted five years, and during this time, Darwin collected many samples, especially from the Galapagos Islands.

During his visit to the islands, Darwin noted that the unique creatures were similar from island to island, but perfectly adapted to their environments which led him to ponder the origin of the islands' inhabitants.

Among those that struck Darwin so greatly were the finches that are now named in his honor. Darwin would later base some of his thought from the supposing that these finches were all descendants of the same lineage.

Evolutionary Principles

• Descent with Modification - Darwin proposed that subsequent generations exhibited small changes that eventually built up in a population over time, leading to great change

• Variation – Darwin compared wild a domesticated species and noted many variations. He suggested the source of variation was “reproductive elements prior to conception.”

• Adaptation – Observations in the Galapagos led him to theorize that animals that are better suited to their environment produce more offspring and that eventually leads to change of the entire population.

Modes of Selection

• Natural Selection – individuals that have inherited beneficial adaptations produce more offspring than do other individuals, therefore only adaptations that give an advantage tend to stay in a population

• Artificial Selection – humans intervene and breed for certain purposes and traits

• Sexual Selection – the ability to produce offspring is dependent on one or more individuals choosing a mate based on desired traits or abilities

Natural Selection

• Natural selection is a mechanism by which individuals that have inherited beneficial adaptations produce more offspring on average than do other individuals.

Four Main Principles of Natural Selection

• Variation– The heritable differences in every population are the basis

for natural selection• Overproduction

– Having many offspring ensures that many will survive, but also increases competition

• Adaptation– Some variations make some individuals better suited for

their environment• Descent with Modification

– Over time, all individuals will exhibit the beneficial trait

Darwin’s Evidence

• Fossils – Scientists look to fossils to study long periods of time and how organisms changed

• Geography – comparing species in one island to species on other islands and even mainland South America led Darwin to believe that the land masses were once joined

• Embryology – Studying how an organism develops illuminates similarities among species

• Anatomy – Comparing body parts of different species also shows similarities that suggest a common ancestor

Anatomical Structures as Evidence

• Homologous Structure – a similar structure that appears in different organisms and has different functions

• Analogous Structure – structures that performs a similar function but are not similar in origin

• Vestigial Structure – remnants of structures or organs that had a function for early ancestors but are no longer needed or functioning in the modern population

Genetic Variations

• Genetic variation in a population increases the chance that at least some individuals will survive

• Genetic variation comes from several sources:– Mutation – a random change in DNA of a gene– Recombination – new allele combinations formed

in offspring

Studying Genetics• The combined alleles of all the individuals in a population is called the

gene pool.• Scientists study how frequently alleles occur in a gene pool.• Sometimes, certain alleles move from one population to another

through interbreeding or migration. This is called gene flow.• However, completely due to chance, some alleles either disappear or

become more frequent (or fixed) in a population over time. This is called genetic drift.

• Genetic drift usually only happens in small populations causes to loss of genetic diversity. There are two types:– Bottleneck Effect – genetic drift that happens after a catastrophe greatly

reduces the population size– Founder Effect – genetic drift that occurs after a small population colonizes an

new area

How a Species is Made

• Reproductive Isolation – when members of different populations can no longer successfully mate with one another

• Behavioral Isolation – caused by differences in courtship or mating behaviors

• Geographic Isolation – physical barriers prevent mating of populations

• Temporal Isolation – timing prevents mating between populations

• Speciation – the rise of two or more species from one common ancestor

Patterns in Evolution

• Convergent Evolution – two species evolve toward similar characteristics

• Divergent Evolution – closely related species evolve in different directions

• Coevolution – two or more species evolve is response to changes in each other

• Extinction – a species as a whole is unable to adapt to changes in its environment and dies out

• Punctuated Equilibrium – pattern of speciation that states that episodes of speciation occur suddenly

• Adaptive Radiation – diversification of one ancestral species into many different species

Predicting Genotypes in a Population

• Hardy-Weinberg Equilibrium – used to predict the frequency of genotypes in a population

•p2+2pq+q2=1

Hardy-Weinberg Disclaimers

• In order for a population to be in Hardy-Weinberg Equilibrium, it must fulfill 5 criteria– Large population– No immigration or emmigration– No mutations– Random mating– No natural selection