Theories of Evolution Development of Theories

Change The only constant in the universe is change. Species HAVE changed over time. Many species have come and gone, and new species have emerged. Scientific evidence suggests that all of life is united by descent from the first microbes that appeared on early Earth.

Ideas 1859 -- Darwin published The Origin of Species evolution -- all of the changes that have transformed life over time Before Darwin, 2 ideas prevailed species do not change Earth is less than 10,000 years old and unchanging

What was the name of Darwin’s book? The Origin of Species

Jean-Baptiste Lamarck (1744-1829) First person to suggest that life evolved The law of Use and Disuse Inheritance of acquired characteristics

Lamarck believed that giraffes stretched their necks to reach food Lamarck believed that giraffes stretched their necks to reach food. Their offspring and later generations inherited the resulting long necks

Do you believe this is true?

THIS IS FALSE. an acquired characteristic would have to somehow modify the DNA of specific genes in order to be inherited. But, he was the first to propose that species change according to their environment.

Charles Darwin

Darwin’s Observations The Voyage of the Beagle 1831: HMS Beagle started trip around the world mission -- chart the South American coastline Darwin's main interest was to study the geology, plants, and animals encountered on the voyage. 5 year trip

How long was Darwin’s trip?

Observations Lead to a Question 13 species of finches unique to Galápagos islands ALL most closely resemble 1 finch species living on the South American mainland. The hypothesis: the islands were colonized by a single finch species that strayed from the mainland -- This bird adapted differently to the different habitats on each island key characteristic of the finches -- beaks adapted to the foods available on the each island How did these different beaks arise? -- through natural selection

The Origin of Species Darwin’s book Darwin's Two Main Points First, species of organisms living on Earth today descended from ancestral species. Early organisms spread to different parts of the earth Adapted to environment over millions of years. Darwin called this descent with modification. Second, natural selection is the mechanism for evolution. process by which individuals with inherited characteristics well-suited to the environment leave more offspring on average than do other individuals.

What is Natural Selection?

Most giraffes used to have short necks, but some had slightly longer necks. When the food on the lower branches was eaten, many of the giraffes with shorter necks died of starvation, leaving the ones with slightly longer necks to survive and reproduced. Through many generations, the giraffes with longer necks became the most common.

Examples of Struggle For Existence A oak tree can produce thousands of seeds each summer. Which seeds will form a tree? One oyster can produce millions of eggs each year. However, most offspring die before reaching maturity, and only a few of those that survive manage to reproduce. Which oyster eggs will survive?

Darwin’s Theory: Natural Selection (Based on his observations) Variation exists within all species Populations always tend to increase The amount of resources is limited There will be a struggle for the available resources Organisms who are most fit will live longer and have more offspring. (The offspring will inherit advantageous traits)

Ideas From Geology Charles Lyell and James Hutton said gradual geologic processes such as erosion could explain the physical features of today's Earth. Mountains, canyons, rivers, etc. Geologic evidence points to 2 conclusions: 1st-- the slow processes of mountain building and erosion shows that Earth must be very old. 2nd-- the slow, gradual processes occurring over vast spans of time causes big changes on Earth. Darwin applied idea of gradual change to the evolution of Earth's life forms.

Why did Lyell and Hutton suggest the Earth was older than previously thought?

Malthus Malthus wrote essays on human suffering, disease, homelessness, and starvation Malthus said these conditions were due to humans reproducing faster than food supplies would allow Darwin applied Malthus's ideas to all species. Production of more individuals than the environment can support leads to a struggle for existence. This concept helped Darwin to propose a mechanism of evolutionary change.

Can you name an example where organisms struggle for survival?

Pesticides = Natural Selection in Action Pesticides: poisons used to kill insects 100’s of insects have developed pesticide resistance Survivor bugs after the first pesticide treatment had genes that somehow enabled them to resist the chemical attack. Survivor’s offspring inherited the genes for pesticide resistance. A pesticide does not create resistant individuals, but selects for resistant insects that are already present in the population.

Artificial Selection = Humans Choose Traits selective breeding of plants / animals produce offspring w/genetic traits that humans want plant breeders improve traits -- grain production, disease resistance, protein content animal breeders select for growth rate or temperament Breeders play the role of the environment, allowing only those plants or animals with desired traits to reproduce.

Origin of Variation 1.) Genetic Recombination (Sexual reproduction. Meiosis, Crossing over and random fertilization) 2.) Mutation (Produces New Genes)

Factors which Change Genetic Equilibrium (ie. Cause Evolution) 1. Natural Selection: Favoring one genotype over another. Ex. H. B. Kettlewell

Types of Selection a) Directional Selection- constant genetic change of one type. Ie. Giraffe’s necks getting longer. Dinosaur size increasing

Types of Selection b) Stabilizing Selection- Selection that favors the average and eliminates the extremes. The population becomes more alike

Siberian Huskies – sled dogs (35-60 lbs.) Too heavy – too slow and potentially sink in snow Too light – not strong enough to pull sleds The population all becomes similar to each other

Types of Selection c) Disruptive selection- Selection that favors the extremes and eliminates the average. Population becomes more different. This can lead to new species

Meteor hit Earth 65 mya Food was depleted, dust blocked the sun, tsunamis and wildfires were plentiful. Larger (average) animals who need lots of oxygen and food, died out quickly.

Types of Selection

Factors which Change Genetic Equilibrium (ie. Cause Evolution) Gene flow- Movement of organisms in or out of a population Mutation- change in a gene form that is unequal. Ie. Change form gene A to a more than a to A. Genetic Drift- change in gene frequency due to random chance (some genotypes may mate more than another just due to chance) Isolation- separation of a population so it can’t interbreed. Either genetic or geographic

Patterns of Evolution Divergent evolution-Two separate species becoming more different due to different selective pressures in different environments (human foot vs. ape foot) Adaptive Radiation- process by which species adapt to a variety of habitats Speciation- formation of two separate species from one (different species can no longer breed)

Divergent Evolution Different selective pressures caused different traits to become more common in certain environments.

SPECIATION

2. Convergent Evolution- the process by which distantly related organisms become more similar due to similar selective pressures in similar habitats