The Process of Evolution

Darwin’s Theory of Evolution

• The theory of evolution explains how a species or type of organism changes over time.

• The theory of evolution was first proposed by the English scientist Charles Darwin.

Darwin’s Theory of Evolution• Darwin traveled on H.M.S.

Beagle to a group of isolated islands off the coast of South America called the Galapagos Islands.

• His studies in the Galapagos Islands lead to his publishing the book On the Origin of Species. It was in this text that Darwin first presented his ideas on evolution.

Darwin’s Theory of Evolution

• Darwin studied a group of birds called finches while on the islands. He noted that some species of finches were very different from each other in the shapes of their beaks.

Darwin’s Theory of Evolution

• Darwin suggested that these species of finches shared a common ancestor and that, over time, each species’ had adapted beaks suitable to the type of food that was available on their particular island.

Darwin’s Theory of Evolution

How does evolution occur?

A Struggle for Existence

• Though a plant may produce hundreds of seeds, only a few of those seeds will grow into mature plants.

• In fact only a relatively small number of offspring of any species survive to produce their own offspring…why?

A Struggle for Existence• Organisms must compete for

limited resources such as food and shelter.

• Organisms must cope with predators, animals that feed on other animals and parasites, organisms that live on or within another organism.

• Organisms must be able to handle extremes of climate such as heat and cold.

Genetic Variation• You may have your “mother’s

ears” or your “grandfather’s eyes”.

• By way of reproduction, characteristics are passed on from parents to offspring.

• The resulting offspring resemble their parents and each other, however; they show some differences.

• The differences among offspring are called genetic variations.

Genetic Variation

Genetic variation can occur in either one or two ways.

• The traits of the offspring are the result of a new assortment of traits inherited from both parents.

• Mutations, or sudden changes may occur in the genetic material of an organism.

Genetic VariationTypes of Genetic Variation

• Structural or anatomical: differences in the body of an organism (muscle size or thickness of fur).

• Physiological: differences in the functioning of the organism (resistance to disease, digestion).

• Behavioral: differences in how an organism reacts (mating display, feeding time).

Genetic Variation

Types of Genetic Variation

• Chromosomal and genetic: differences in the arrangement of genetic information along the chromosomes.

• Molecular: differences in molecules that make up an organism and allow it to function (enzymes).

Summary …• There is a struggle for existence, which limits the number of

survivors.

• There are differences among offspring due to individual variations.

That being the case …. What decides which individuals survive to reproduce and become parents of the next generation?

Natural Selection• Special characteristics

that make an organism well suited to a particular environment are called adaptations.

• Whatever slight variations an organism has that gives it an advantage over other organisms would make it more likely to survive and pass on its genetic variations to future offspring.

Natural Selection

• The process, whereby conditions of life determine which organisms have survival advantages and are more likely to reproduce is called natural selection.

• The gray moth in this picture is more likely than the black moth to survive and reproduce.

Artificial Selection

• The selection by humans of organisms with specific, desired characteristics is known as artificial selection.

Antibiotic Resistant Bacteria

Evidence for Evolution

Creating a Family Tree• Biologists try and understand

the relationships that exist among different species.

• Simple diagrams can be used to represent these relationships.

• These diagrams can illustrate which animals evolved from common ancestors and at what time in the past this occurred.

Homologous and Analogous Structures

• One way to determine the relationship among organisms is to find characteristics they share that they inherited from a common ancestor. These similar features are called homologous structures.

• The forelimbs of these four animals are homologous – they are all made up of the same types of bones.

Homologous and Analogous Structures

• Not all similarities mean that organisms evolved from a common ancestor.

• When organisms evolve similar traits because they live in similar environments we call that process convergent evolution.

• The features shared by the organisms through convergent evolution are called analogous structures.

Evidence From Fossils• Fossils are traces or remains

of dead organisms that have been preserved by natural processes.

• Fossils can be formed when organisms are trapped in amber or in ice. Fossils can be formed by the gradual replacement of the organism’s remains by other substances. Fossils can be formed if the plant or animal creates an impression.

The Age of Fossils• A fossils relative age can be

determined by observing the layers of sedimentary rock in which the artifact was found.

• The age of the fossils found in the layers can be related to the ages of the layers..

• This method in which we are able to determine if one fossil is younger or older than another is called relative dating.

The Age of Fossils

• Determining when the fossil was actually formed is called absolute dating and depends upon radioactive isotopes.

• Over time, radioactive isotopes decay into different elements. By measuring the amount of each element present in the sample, the length of time since the fossil was formed can be calculated.

• For example, over time carbon-14 will decay into carbon-12. Carbon dating can be used to date the remains of living organisms that are less than 50,000 years old

Evidence From Comparative Anatomy

• Organisms may have body structures which have no function but are similar to more fully developed structures in another organism – these are called vestigial structures.

• Humans posses a vestigial structure called the appendix at the base of the small intestine. The appendix is similar to the cecum in rabbits which is used to digest plant materials.

Evidence From Comparative Anatomy

• The fact that a similar organ in one species is still useful is evidence that humans evolved from an ancestor that once had this larger, functional structure.

• These vestigial structures support the idea that species have evolved over time as a result of natural selection.

Evidence From Comparative Embryology

• Embryos of various organisms are surprisingly similar.

• At this first stage of their development, each of these embryos has a tail and slits in its neck.

• These similarities indicate that long ago these animals shared a common ancestor.

Evidence From Comparative Biochemistry

• Biochemistry is the chemistry of living things.

• All organisms store genetic information that is passed on from one generation to the next in DNA molecules in a manner that is almost exactly the same.

Evidence From Comparative Biochemistry

• Proteins are molecules in living organisms used to build structures, to transport materials, to send signals, to provide defense and to control metabolic activities.

• Proteins from different species can be compared. Those species with the fewest differences are more closely related.

Evidence From Comparative Biochemistry

• During DNA hybridization, DNA from two different organisms can be compared to see how similar they are.

• The more similarities the more closely related the species are.

Patterns of Evolution

• Most often as species evolve from a common ancestor they become increasingly different from each other – this is known as divergent evolution.

• Animals that are not closely related but have developed similar adaptations exhibit convergent evolution.

Patterns of Evolution

• Parallel evolution is when two distinct species which have evolved from a common ancestor continue to change in similar ways.

• Both pterodactyls and birds developed the body structures necessary for flight separately from each other.

Patterns of Evolution

• Because the environment always includes other living organisms, species frequently change because of, or along with, changes in species around them.

• Evolving alongside another species is called coevolution.

Pace of Evolution• Researchers disagree

about the details of the process of evolution.

• When evolution occurs through small, steady steps, we call the process gradualism.

• When evolution occurs in sudden big jumps with long periods of little or no change, we call the process punctuated equilibrium.

Extinction• Extinction is the

disappearance of a species from Earth.

• Extinction occurs when a species is no longer able to produce more members of its own type because it can not adapt to the environment.

• Human activities have had a significant impact on the rate of extinction.

• Before a species becomes extinct they become endangered – examples include the African elephant and giant panda.

Taxonomy• Taxonomy is the science of

naming and classifying organisms according to shared characteristics.

• Organisms are grouped according to their evolutionary relationships – the smallest group is the species, similar species placed together in a larger group called genus.

• Kingdom, Phylum, Class, Order, Family, Genus, Species.

Taxonomy• The five main Kingdoms

include: Monera, Protists, Fungi, Plants and Animals.

• The scientific name of a species consists of two parts – the first part is the genus, the second part is the species or specific name.

• For example a red oak is Quercus rubra, a white oak is Quercus alba. This taxonomic naming system is called binomial nomenclature.

The Search for Human Origins

• About 130 million years ago, reptiles such as dinosaurs were the dominant large animals on Earth – in a relatively short period of time, they became extinct.

• About 70 million years ago, faced with fewer reptile competitors, an enormous variety of mammals evolved.

The Search for Human Origins• One groups of mammals

called primates, used opposable thumbs to adapt to life in trees.

• The order of primates includes prosimians, monkeys, apes, and humans.

• The higher primates including apes and humans are known as hominids.

Hominids: The Earliest Humans• Approximately 20 million years

ago, large changes in climate caused forested areas to diminish.

• An African Ape evolved and that became the common ancestor of both chimpanzees and humans.

• This does not mean that our ancestors were chimpanzees – it does mean that we are closely related.

Why Did Early Hominids Walk on Two Feet.

• Our earliest hominid ancestors lived in the trees – due to a changing environment, there was a shift from the forests to the open grasslands.

• By being upright in the grasslands, early hominids could see danger approaching.

• This could be a tremendous evolutionary advantage and could have easily led to the evolution of life on two feet.

Our own Genus• Hominids in the genus Homo

are characterized by having large brains, which sets them apart from all other primates.

• Homo erectus is considered to be the first ancestor within our genus.

• H. erectus was known to build fires, live in caves, wear clothes and manufacture tools

Our own Genus• Homo erectus colonized a

variety of places in Africa, Asia, Europe and Australia.

• These early humans included the Neanderthals and the Cro-Magnons, known for there large brains, tools, and clothing.

• Our own species, Homo sapiens evolved from H. erectus – exactly where and when is still being debated.