Evolution

The Big Bang Theory

• The origins of the universe are one of the great mysteries of our world

• While we have no first-hand evidence of the formation of the universe, we do have substantial secondary data

• These various forms of evidence have led to the formation of the Big Bang Theory

• Key stages to consider in the formation of our universe include:

  1.) The Big Bang (13.8 billion years ago)

  • The universe began as a hot, dense point

  • Space, time, and matter were created

  2.) Inflation (Fractions of a second after the Big Bang)

  • The universe expanded faster than the speed of light for a very short time

  • This made the universe smooth and uniform

  3.) Formation of Fundamental Particles (First few seconds)

  • Energy turned into quarks, electrons, and neutrinos

  • Quarks combine to form protons and neutrons.

  4.) Nucleosynthesis (3-20 minutes after the Big Bang)

  • Protons and neutrons fused to create hydrogen, helium, and lithium nuclei

  • The universe was too hot for atoms to form yet

  5.) Recombination (380,000) years later - Formation of Atoms

  • Electrons joined with nuclei to form neutral atoms

  • The light was finally able to travel freely, creating the Cosmin Microwave Background (CMB)

  6.) The Dark Ages (After recombination - a few hundred million years)

  • The universe was mostly dark and filled with gas

  • No stars or galaxies existed yet.

  7.) Formation of Stars and Galaxies (A few hundred million years later)

  • Gravity pulled hydrogen and helium together to form the first stars

  • Stars grouped into galaxies, including the Milky Way

  8.) Formation of Our Solar System (4.6 billion years ago)

  • A giant cloud of gas and dust that collapsed, forming the sun

  • the leftover material formed planets, moons, and asteroids

  9.) Present-Day Universe

  • The universe continues to expand

  • Stars are born and die, forming new elements

  • scientists study dark matter and dark energy to understand the future of the universe

The Formation of Chemical Elements

• Chemical elements are substances that ordinary chemical processes cannot decompose into simpler substances.

  • The number of protons in their nucleus makes them different from one another

  • Some of the most common elements in living things include: Carbon, Hydrogen, Oxygen, Nitrogen, and Phosphorus.

• The first elements to form were also the simplest: Hydrogen and Helium were the first to form and are key to the fusion reactions occurring within stars.

  • One of the main sources of energy in the universe (and therefore on Earth) is solar energy

• The name of the theory which best explains the formation of the solar system is called the Solar Nebula Theory

  • About 4.6 billion years ago, a huge cloud of gas and dust floated in space

  • It began to spin, and the high-density high-pressure core became a protostar, and eventually, the sun

• Evidence for solar nebula theory includes:

  • The placement of the rocky planets, then the gas giants both with the debris that never became a planet between them

  • All planets orbit in the same direction

  • Some meteorites are 4.6 billion years old, the same age as the sun and planets

The Conditions of Early Earth

• 4.6 billion years ago

  • The atmosphere was toxic: CH4, H2, H2O, N2, NH3)

  • There was substantial volcanic activity

  • Meteorite impacts were a regular occurrence

  • Temperature changes were extreme (due to the lack of ozone & those factors listed above)

Key events in Early Earth

• Key events in the formation of Early Earth:

  • Formation of Earth (4.6 billion years ago)

  • First life (prokaryotic bacteria, 3.5 billion years ago)

  • Photosynthesis evolved (2.5 billion years ago)

  • Oxygen revolution (2.4 billion years ago)

  • First multicellular organisms (600 million years ago)

  • First land plants and animals (500 million years ago)

  • First mammals and dinosaurs (230 million years ago)

  • First humans (200,000 years ago)

The Evolution of Photosynthesis

• The jump from single-celled life to complex multicellular life:

  • The jump from simple life to complex life begins 2.4 million billion years ago

    • Photosynthesis: A ‘mistake’ mutation

      • using sunlight to turn into food

    • Cyanobacteria - the first bug to use photosynthesis

    • The cyanobacteria thrive, but the waste product is oxygen, which accumulates in the atmosphere, leading to significant changes in Earth's environment and paving the way for aerobic life forms.

  • Most of life on earth is killed off by oxygen, leading to the evolution of new species that adapted to utilize oxygen for respiration, ultimately resulting in a diverse array of aerobic organisms.

    • As oxygen was released, it changed the entire chemistry of the planet

    • it reacted with the earth’s atmosphere, turning the planet very cold - a snowball planet (lasts for 200 million years)

    • After volcanos rewarm the earth, multicellular organisms thrive and they use oxygen to survive.

• What is photosynthesis

  • The process by which plants and other autotrophs can convert solar energy into chemical energy

  • The first organisms to evolve the ability to do photosynthesis were bacteria, specifically cyanobacteria

  • One of the waste products of photosynthesis is oxygen, which over millions of years changed the composition of the Earth’s atmosphere.

    • Organisms that can exist in the presence of oxygen are called aerobes while those that cannot are anaerobes

The Rate of Speciation

• Speciation is the process through which new species form

• It has been a critical process over the billions of years during which life has evolved on our planet

  • It occurs through natural selection

  • The rate of speciation has been inconsistent over our planet’s history

• The primary influencing factor on changes in speciation rate is environmental conditions

  • Under some conditions, selection occurs quickly or radically

  • Consider a species of snails that had been living with the same basic form for many thousands of years, layers of their fossils would appear similar for a long time.

  • When a change in the environment takes place, such as a drop in the water level, a small number of organisms are separated from the rest in a brief period

  • , essentially forming one large and one tiny population, the tiny population faces new environmental conditions

  • Because its gene pool quickly became so small, any variation that surfaces and that aids in surviving the new conditions becomes the predominant form.

What is Evolution

• Evolution is the change in the heritable characteristics of biological populations over successive generations

• A population is a group of individuals of the same species living in the same place at the same time which can interbreed

  • Individuals cannot evolve in the biological sense

• Before Darwin:

  • Jean-Baptiste Lamarck: Organisms adapt to their environment

  • Georges Cuvier: organisms change over time (fossil evidence)

  • Charles Lyell: the Earth is billions of years old (geological changes)

  • Thomas Malthus: overproduction (economic models)

  • Charles Darwin: Natural Selection

Who was Charles Darwin

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• Charles Darwin was born in 1809, the son of a wealthy English society doctor, he began to formulate his theory in the 1830s and spent almost 20 years perfecting it before he published his book On the Origin of Species

• Alfred Wallace was born in 1823, the son of an English mother and Scottish father who struggled financially

• Both men were naturalists, they studied patterns in nature and were eager to explore the world to study more new species.

• In 1858, just one year before Darwin published his book both men presented their ideas to the Linnaean Society and both men’s ideas were very simillar

What is Natural Selection

• Natural selection occurs through the following mechanism:

  • 1.) Variation: Within a population of one species, there is genetic diversity, which is called variation

  • 2.) Adaptation: Due to natural variation, some individuals will be fitter than others

  • 3.) Overproduction: Fitter individuals have an advantage and will reproduce more successfully than individuals who are less fit.

  • 4.) Descent with modification: The offspring of fitter individuals may inherit the genes that give that advantage

    
    

Differing Selection Pressures

• A selection pressure is an evolutionary force that causes a particular phenotype to be more favorable in certain environmental conditions

• A trait that gives only small benefits to survival and/or reproduction has a low selecting pressure (such as slightly better food gathering)

• A traut that gives significant benefits to survival and/or reproduction has a high selection pressure (such as antibiotics and bacteria)

• Many pests have evolved resistance to pesticides over time

  • Pesticides are chemicals that are designed to kill pests such as insects that eat crops

Sources of Variation

• sexual reproduction is one of the most significant ways in which genetic variation enters a population

  • When two parents combine their haploid gametes this significantly increases the variation in their offspring and the more chromosomes the species have (n) the more possible combinations there are.

  • 2^n = possible combinations where “n” is the haploid number of a species

  • Sexual reproduction requires considerably more work, more risk, and more energy consuming than asexual reproduction.

• Throughout the process of meiosis and sexual reproduction, there are several other ways in which variation is increased.

• 1.) Independent Assortment of chromosomes in Metaphase I and II or meiosis

• 2.) Crossing over of non-sister chromatids on homologous chromosomes during Prophase I or meiosis

• 3.) Occurs during interphase and is completely random: Mutations

  • They can be harmful, beneficial, or neutral

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Evidence for Evolution

• A theory is a well-substantiated explanation of an aspect of the natural world that can incorporate laws, hypotheses, and facts

  • To substantiate the theory of evolution we require evidence, there are several types which we will discuss

• What is a fossil?

  • Fossils can be formed in many ways and may be considered trace fossils or body fossils

  • Trace fossils are fossils of footprints, trails, burrows, feces, or other trace of an animal rather than of the animal itself.

  • Body fossils are the remains of plants, animals, and microorganisms preserved in a geologic context and are what most people think of when they think of a fossil

• Fossil Evidence: types

  • From Body fossils (preserved bones, teeth, shells, etc.):

    • What the organism looked like (size, shape, structure)

    • How species have changed over time (evidence for evolution)

    • What the organism ate (from teeth shape and stomach contents)

    • Relationships between species (comparing fossils to modern organisms)

  • From Trace fossils (Footprints, burrows, feces, etc.)

    • How the organism moved (walking running, or slithering)

    • Where and how it lived (habitat and behaviors)

    • Social behavior (whether it lived alone or in groups)

    • Diet and digestion (from fossilized feces, called coprolites)

  • Both types of fossils help scientists reconstruct past ecosystems and understand how life evolved over millions of years.

• Fossil Evidence: Dating

  • The ability to determine the age of a fossil is important to understanding its role in evolution

  • It is relatively easy to determine the relative age of a fossil (which is older and which is younger) while the absolute age (in years) is much more complex to determine

  • The absolute age of a fossil is determined based on the rate of decomposition of an isotope incorporated into the organism while it was alive or environmental cues (like volcanic ash)

  • Based on how much the isotope has decayed and how fast the rate of decay occurs the age in years can be determined

  • Absolute age can be determined with carbon dating, carbon is incorporated into living things during their lifetime and then after they die it slowly decomposes into N-14

  • The number of years it takes for half of the C-14 to decay into N-14 is called the half-life and it is 5730 years, so we determine how many half-lives have gone by and then multiply that number by 5730 to determine the age of the fossil.

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