Spontaneous Generation

• The idea that life arises from non life

ex. Damp hay and corn in a dark corner give rise to mice.

• Francesco Redi showed that flies and maggots did NOT arise spontaneously from rotting meat.

• Redi hypothesized that flies, no meat, produced other flies.

• In a closed jar with meat in it, no flies were produced.

• In an open jar, maggots formed, leading to flies.

Theory of Biogenesis

• States only living organisms can produce other living organisms.

Pasteur’s Experiment

• Pasteur’s experiment showed that sterile broth remained free of microorganisms until exposed to air.

Origin of Life

• Alexander Oparin and John Haldane suggested the primordial soup hypothesis about the origin of life.

• They thought that if Earth’s early atmosphere had a mixture of certain gases, organic molecules could have been synthesized from simple reactions.

• They thought the sun and lightning might have been the energy sources.

Miller/Urey Experiment

Miller/Urey Experiment

• The two scientist took the hypothesis proposed by Oparin and Haldene and tested it with a glass apparatus.

• They showed for the first time that organic molecules could be produced from gases proposed to have made up the atmosphere of early Earth.

Earth’s early Atmosphere

• Gases that likely made up earth’s early atmosphere:

• H2O –Water• CO2-Carbon Dioxide• SO2- Sulfur Dioxide• CO-Carbon Dioxide• H2S-Hydrogen Sulfide• HCN-Hydrogen Cyanide• H2-Hydrogen• NO FREE OXYGEN (O2)

How the first organic molecule originated:

• Amino acids are not sufficient for life.

• Life requires proteins (many amino acids link together to form a protein)

• In the Miller/Urey experiment amino acids could link together, but did not stay linked.

• One possible mechanism for linking them together would be clay sediment.

First Genetic Code

• RNA was life’s first coding system.

• All organisms contain RNA.

• RNA sequences have changed little over the time.

• RNA can behave like an enzyme.

• Some scientists hypothesize that clay particles could have provided the initial template for RNA replication.

Cellular Evolution

• Fossilized microbes were found in rock 3.5 billion years old.

• This proves that cellular activity had become established very early in Earth’s history.

• Also suggested that early life might have been linked to volcanic environments.

The First Cells

• First cells were prokaryotic.

• Recall that prokaryotic cells are:– Smaller than eukaryotic cells– Lack defined nucleus and other organelles

There are two types of prokaryotic cells:

1. Eubacteria

2. Archeabacteria

Archeabacteria

• Closest relative to Earth’s first cells.• Live in extreme environments, such as hot

springs of Yellow Stone park or the volcanic vents of the deep seea.

• Live in environments similar to earth’s early atmosphere.

• Can live without oxygen.• Chemoautotrophs-get there energy from

chemicals.

Introduction of Oxygen to Earth’s Atmosphere

• 1.8 billion years ago oxygen appeared in the atmosphere.

• The oxygen normally combined with iron to produce iron oxide.

• Earth’s free iron was saturated with free oxygen.

• This caused oxygen to start accumulating in earth’s atmosphere.

Photosynthesizing Bacteria

• Photosynthesizing prokaryotes evolved not long after the archaea.

• Primitive photosynthesizing prokaryotes were called cyanobacteria.

• Cyanobacteria eventually produced enough oxygen to support the formation of an ozone layer.

• This eventually lead to right condition for the appearance of eukaryotic cells.

Endosymbiont Theory

• Eukaryotic Cells appeared in fossil record about 1.8 billion years ago. (same time when oxygen appeared)

• Recall that Eukaryotic cells:- Have a nucleus and membrane bound organelles.- Remember mitochondria is the site of cellular respiration and chloroplasts (Found only in plant cells) are the site of photosynthesis._

• Both mitochondria and chloroplasts are the same size has prokaryotic cells.

• The contain prokaryotic features that lead scientist to believe that prokarytoic cells were involved in the evolution of eukaryotic cells.

Endosymbiont Theory

• 1966 biologist Lynn Margulis proposed the endosymbiont theory.

• According to this theory, eukaryotic cells lived in association with prokaryotic cells.

• In some cases, prokaryotic cells lived inside of eukaryotic cells.

• Could have entered the cell through endocytosis (like most large molecules)

• The relationship was mutually beneficial and eventually the prokaryotic cells became the organelles in Eukaryotic cells.

• EVIDENCE TO SUPPORT THEORY-Mitochondria and chloroplasts have their own circular DNA (just like prokaryotic cells)

-Mitochondria and chloroplasts have their own ribosomes that resembles prokaryotic ribosomes.

- Mitochondria and chloroplasts reproduce asexually by fission, independent from the rest of the cell.

The Origins of Evolutionary Theory

• Evolution refers to the process by which a species of organisms change over time.

• The concept of evolutionary change in organisms is most often associated with the British naturalist Charles Darwin.

• Darwin published the book On the Origin of Species by Natural Selection in 1859.

• Darwin’s ideas built on the work of several other scientists working in a variety of fields.

1. Charles Bonnet:

• The Swiss naturalist Charles Bonnet is credited with being the first person to use the term evolution to refer to organisms.

• Bonnet was studying fossils when he noticed that many of the fossils he examined did not resemble any living animals.

• Bonnet developed a hypothesis called catastrophism to explain these observations. His hypothesis included two main ideas:

1. Earth was subjected to periodic catastrophes that affected the entire planet, killing all living things. Fossils were the remains of those now dead life forms.

2. Following each catastrophe, new life emerged. All these new life forms were slight improvements over earlier life forms. These improved life forms resulted from evolution.

2. Jean-Baptiste Lamarck:

• In 1809, the French biologist Jean-Baptiste Lamarck proposed a new theory of evolution. Lamarck thought that organisms evolved by acquiring characteristics during their lifetimes and then passing on those traits to their offspring. The classic example of Lamarck’s theory of inheritance of acquired traits is the giraffe.

• Lamarck believed that organisms changed due to the demands of their environments.

• In the case of giraffes, Lamarck proposed that the neck of the giraffe become longer during its lifetime because it had to stretch to reach leaves on high branches.

• He also thought that those giraffes passed the acquired trait of a longer neck to their offspring. As a result, over many generations, all giraffes acquired long necks.

• A second part of Lamarck’s theory is the principle of use and disuse.

• Lamarck that the parts of its body an organism used became stronger and would be passed on to offspring.

• By contrast, if an organism did not use a part of its body, that structure would disappear or be lost in future generations.

Influences on Darwin

• In 1831, the British ship H.M.S Beagle set sail on a scientific expedition that covered nearly 65,000 kilometers over five years. Charles Darwin was the naturalist for the expedition. Darwin’s main job was to identify areas suitable for mining.

• Darwin was heavily influenced by the readings of two scientists while on his trip:

Charles Lyell:

1. During the expedition, Darwin read Charles Lyell’s book Principles of Geology.

• Geology is the scientific study of Earth and its features.

• The planet’s great age is important to understanding both geological and biological evolution.

2. Thomas Malthus

• Darwin also read Thomas Malthus’s An Essay on the Principle of Population.

• Malthus wrote that populations will naturally outgrow their food resources, leading to competition for food.

• Organisms will compete for food both with members of their own species and with organisms of other species.

Darwin’s Observations

• Darwin notices a great diversity and a very large number of species. In a South American rain forest, he collected 68 different species of beetles in one day.

• Darwin observed that plants and animals were suited to the environments in which they lived.

• 3. He noticed that different species live in similar ecosystems. For example, Darwin compared grasslands in South America and Australia. The grasslands on the two continents on the two continents had very different animals.

• 4. During his voyage, Darwin began to look at the fossil record. He collected many fossils in South America. When he examined his finds, he observed that some of the fossils resembled modern animals. Others looked very different from any modern organisms.

• Darwin observed the different plants and animals on a group of islands called the Galapagos.

• The islands are close together, but their climates differ greatly.

• The low-lying islands are dry, hot, and sparsely vegetated.

• The islands that have higher elevations get more rain and have much more diverse plant life.

• Darwin also studied the animals of the Galapagos.

• He saw that the shells of land tortoises differed depending on where they lived.

• Tortoises with dome-shaped shells and shorter necks (domed tortoises) lived on wet, highly vegetated islands, where they did not need to stretch to reach food.

• On the other hand, tortoises with curved shells and long necks (saddleback tortoises) lived on drier islands. Those tortoises had to stretch to reach the sparse vegetation.

• Darwin also studied the finches that live in the Galapagos.

• He collected specimens of about fourteen different types of finches.

• The finches were all similar except for the structure of their beaks.

• Darwin observed that each finch’s beak was suited to what the bird ate. He also observed that finches in different habitats fed on different things.

Theory of Evolution

• After his voyage, Darwin spent many years studying the information he had collected. From his observations of the tortoises and finches, Darwin developed two concepts that form the basis of the theory of evolution.

1. Natural Selection:

• The idea that organisms with favorable variations for their environment survive, reproduce, and pass those variations on the next generations. The concept of natural selection was based on Darwin’s observations that many of these variations helped species survive.

2.Reproductive isolation:

• A species is a group of organisms with similar characteristics that can breed with one another to produce fertile offspring.

• The organisms Darwin observed on the various Galapagos Islands were separated by the ocean.

• . The physical separations led to reproductive isolation, an inability or organisms to interbreed due to geographic barriers.

• Reproductive isolation allows different populations of a species to adapt to different environments.

• Over time, differences in their adaptations can become significant enough that different species emerge.

Wallace’s Contributions

• Darwin spent many years analyzing his data and developing his theory. At this same time, another scientist, Alfred Wallace, was also formulating a theory of evolution. Wallace believed that evolution resulted largely from competition among populations for resources a concept that built upon the ideas of Thomas Malthus.

• Darwin and Wallace shared their ideas about evolution with each other.

• They agreed that natural selection was part of evolution.

• However, Wallace thought competition was the driving force behind natural selection, while Darwin stressed reproductive success.

• Both scientists published papers on their ideas in 1858.

• Darwin’s book The Origin of Species appeared the following year.