Evolution

Unit 2

What is Evolution?

Evolution: The changing of a population’s genotype (genetics) over time.

Charles Darwin contributed the most to the Theory of Evolution.

Darwin wanted a scientific explanation for the diversity of life on Earth.

1831 – Darwin set sail on the H.M.S. Beagle as the ship’s Naturalist. He returned in 1836.

Biogeography: The study of the distribution of organisms around the world.

Rhea

South America

Ostrich

Africa

Emu

Australia

• His stop at the Galapagos Islands influenced him the most.

• He studied the environments on each of the islands and found a lot of animal diversity.

• He found that the animals on the main land were similar but not identical to those on the islands.

• He kept a collection of specimens and studied his collection from the trip for the rest of his life.

• Turn to page 290 in the book. Read 1^st paragraph under “Main Idea”

Read paragraphs 2 and 3 on page 290.

As mentioned, Darwin studied his Galapagos specimens for the rest of his life.

During his ship voyage he also read Lyell’s book “Principles of Geology”

Lyell and other scientists greatly influenced Darwin and helped provide evidence to support his theory of evolution.

James Hutton and Charles Lyell pointed out that the forces shaping the Earth today (volcanoes, earthquakes, erosion, etc.) must have been the same ones which formed the Earth in the past.

They concluded these processes take large amounts of time so the Earth must be millions of years old.

Occasionally there are sudden, larger changes that happen.

Read page 291 in the book.

Glyptodon

Modern armadillo

Jean-Baptiste Lamarck (French Naturalist in 1809) proposed that animals evolved by the use or disuse of physical structures and passed these traits on to their offspring. He did not provide explanations for how these traits were passed on.

Thomas Malthus (1766-1834)

Wrote “Essay on the Principles of Population” in 1798.

“The power of population is so superior to the power of the earth to produce subsistence for man, that premature death must in some shape or other visit the human race”

He argued that the food supply increase linearly, while population size increased exponentially.

Malthus’ writing would ultimately inspire Darwin’s theory of evolution by natural selection.

Thomas Malthus reasoned that a population allowed to grow unchecked would run out of resources.

Darwin had formulated his theory of natural selection by 1844, but he was wary to reveal his thesis to the public because it so obviously contradicted the biblical account of creation. In 1858, with Darwin still remaining silent about his findings, the British naturalist Alfred Russel Wallace independently published a paper that essentially summarized his theory. Darwin and Wallace gave a joint lecture on evolution before the Linnean Society of London in July 1858, and Darwin prepared On the Origin of Species by Means of Natural Selection for publication.

His book was published on November 24^th, 1859.

Evidence for Evolution

• Fossil Record

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• Embryology (Developmental Biology)

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• Comparative Anatomy

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• DNA and Biochemistry

Fossil Evidence

Fossils can also be molds, casts, imprints, eggs, etc.

Fossils provide some of the strongest evidence of organic evolution.

Most fossils occur in sedimentary rock and require special circumstances for them to form.

Ex. Amber, ice, or buried quickly.

Fossil Evidence

Fossils help us build a time line of the Earth’s history and can tell us a lot about an organism.

• How it lived.
• Where it lived.
• What it looked like.
• It’s age.
• What the environment was like.

Fossil Evidence

The fossil record has gaps and is not complete.

No fossil evidence that contradicts evolution has ever been found.

Embryology (Developmental Biology)

Embryology: The study of how animals are formed from an egg to an infant.

All animal species develop from an egg through a fetus with the same development processes.

Vertebrates have groups of cells that develop in the same order and in similar patterns.

Comparative Anatomy

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Homologous Body Structures

Homo = Same

Homologous body structures suggest a common evolutionary origin. (Comes from a common ancestor)

Ex. The forelimbs of tetrapod vertebrates (four legged animals.)

Comparative Anatomy

Homologous limbs may vary in form or functions but are constructed from the same basic bones.

Comparative Anatomy

Analogous Body Structures

Body parts of organisms that do not have a common evolutionary origins but are similar in function.

Comparative Anatomy

Analogous body structures develop because of similar environments, not a similar ancestor.

Comparative Anatomy

Homologous

vs

Analogous

Comparative Anatomy

Vestigial organ: A body structure in a present day organism that is no longer needed, or is used for a different function.

Ex. Pelvis and femur bones in Whales

Comparative Anatomy

Vestigial organs are reduced in size and possess little to no function.

Ex. Wings on an ostrich

Ex. Legs on skinks or snakes

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DNA and Biochemistry

Since DNA is a universal code and all organisms use the same 20 amino acids, we can analyze and compare DNA sequences and proteins used between species.

Vestigal DNA: DNA that is no longer used but is in the genome. (Found many times in dogs)

DNA and Biochemistry

The more similar the DNA, the more closely related the organisms.

DNA and Biochemistry

Polyploids: Organisms with more than two sets of chromosomes.

This condition is common among plants, and certain groups of fish and amphibians.

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Advantages of being Polyploidy

• Organisms tend to be larger and more vigorous.
• Gene redundancy protects against mutation of deletions.
• Organism can asexually reproduce in the absence of sexual mates.

Disadvantages of being Polyploidy

• Nuclear and cell enlargement.
• Tendency to produce cells with an abnormal number of chromosomes.

DNA and Biochemistry

Darwin’s Theory of Evolution by Natural Selection

Strengths:

1. Lots of evidence.

2. Logical and testable mechanism that could

account for the changes.

3. Variation could result in evolution.

Weaknesses:

1. Did not have a clear explanation for the inheritance of traits.

Natural Selection

Natural selection is the choosing of favorable traits in a population which allows the population to better survive or reproduce. More successful individuals are “naturally selected” to live longer and to produce more offspring that share those adaptations for their environment.

• Natural selection acts on phenotypes, or physical traits, rather than on genetic material itself. New alleles are not made by natural selection – they occur by genetic mutations or recombination. Natural selection can act only on traits that already exist.

• Population: Is all the individuals of a species that live in an area.

Variations

Variation is the difference in the physical traits of an individual from those of those of other individuals in the group to which it belongs.

Variations can occur either among members of different species (Interspecific variation) or among individuals of the same species (Intraspecific variation).

The jaguar population is an example of both variation and natural selection at work. (Pg. 295)

After climate change jaguars that had larger jaws and teeth had a higher fitness than others in the population. Jaguars that ate less didn’t necessarily all die or stop reproducing altogether; they just reproduced a little less.

• Fitness: A measure of the ability to survive and produce more offspring relative to others in the population.

Today large teeth and jaws are considered typical traits of jaguars.

Variations can come from two different sources:

• Recombination: (Crossing Over)

Variations

• Mutations: A random change in the DNA. This change must be inheritable (changes in gametes) to cause changes in the population.

Mutation: A random change in the DNA of a gene. This change can form a new allele. Mutations in reproductive cells can be passed on to offspring. This increases the genetic variation in the gene pool. Because there are many genes in each individual and many individuals in a population, new mutations form frequently in gene pools.

Recombination: New allele combinations form in offspring through a process called recombination. Most recombination occurs during meiosis—the type of cell division needed for sexual reproduction. When gametes are made, each parent’s alleles are arranged in new ways. This shuffling of alleles results in many different genetic combinations.

Speciation: Development of a new species from an existing species.

The greater the variation in phenotypes, the more likely it is that some individuals can survive in a changing environment.

A population with a lot of genetic variation likely has a wide range of phenotypes.

Genetic variation is stored in the gene pool.

Gene Pool: All the genes found in the population

Allele frequency: A measure of how common a certain allele is in the population.

To calculate allele frequencies, count the number of times an allele occurs in the gene pool. Then divide by the total number of alleles for that gene in the gene pool.

Types of Natural Selection

1. Stabilizing Selection (Page 320)

2. Directional Selection (Page 319)

3. Disruptive Selection (Page 321)

Stabilizing Selection:

This selection favors the average individual in a population. (Page 320)

Ex. Human baby size; too small and too large are both problems

Directional Selection:

This selection favors one extreme form of a trait. (Page 319)

Ex. Antibiotic resistance in which bacteria are increasingly unable to be killed by antibiotics.

Ex. Tall sunflowers will get more sunlight.

Disruptive Selection:

This selection favors two extreme forms of a trait. (Page 321)

Ex. Rabbits with black or white fur.

Adaptive Radiation

Adaptive radiation: Occurs when an ancestral species evolves into an array of species to fit a number of diverse habitats.

Hawaiian Honeycreeper (Page 299)

Adaptive Radiation is a type of divergent evolution.

Convergent evolution: Distantly related organisms evolve similar traits due to environmental pressures.

Competition: When a species must compete or fight for a limited resource.

If there is less food or resources, then competition will increase

Ex. Brook trout vs cutthroat trout

Competition between viable mates can lead to morphological changes

Ex. Male peacock’s feathers being more elaborate to attract the peahen

Morphology: The form and structure of animals and plants. (Physical change or feature)

Ex. Panda bears have evolved an extra “thumb” on its hands to better feed on bamboo. (Pg. 297)

Ex. Jaguar with larger skull or teeth. (Pg. 295)

Reproductive Isolation: When two formerly interbreeding populations can no longer mate and create fertile offspring.

Reproductive isolation can happen due to different factors such as geographic, genetic, behavioral factors, or temporal isolation.

Reproductive Isolation

Reproductive Isolation (cont.)

Geographic Reproductive Isolation – Populations are separated by a physical barrier.

Examples: Islands in the oceans, large rivers, Grand Canyon

Genetic Reproductive Isolation – Populations have different chromosome numbers.

Ex. Polyploidy: An individual or species with multiple set of the normal chromosomes. This is the fastest form of speciation because it results in immediate reproductive isolation.

Sexual Selection: The choosing of a mate due to specific physical or behavioral traits.

Behavioral Reproductive Isolation – Populations are physically able to mate but do not due to behavioral issues such as courtship or mating behaviors.

Examples of Behavioral Reproductive Isolation

• Female birds choosing mates due to dances, songs, or behaviors

• Patterns of flashes by fireflies (Pg. 333)

• Cow elk breeding with the bull who wins the fight

Over 2000 species of fireflies are reproductively isolated due to different courtship/mating behaviors. Male and female fireflies produce patterns of flashes that attract mates of their own species. For example, Photuris frontalis emits one flash every second, P. hebes emits one flash every 2 seconds, and P. fairchildi produces a double flash every 5.5 seconds.

Birds of Paradise Video

Some behavior changes can lead to increased competition for limited resources.

Bowerbird video

Temporal Isolation: When different mating times prevent reproduction between populations.

If there is a lot of competition for mates, some members of a population may show signs of courtship at different times. Reproductive periods may change to a different time of the year or a different part of the day. These differences in timing can lead to speciation.

Example: Trout

Objective 4: Explain the role of group behavior on individual species’ ability to survive and reproduce.