Evolution

is the process of biological change by which descendants come to differ from their ancestors.

Darwin was struck by the variation of traits between species of finches in the Galapagos Islands. The most striking difference among them are their beaks.

Their beak shapes seemed well suited to their diets. These observations led Darwin to realize that species may somehow be able to adapt to their surroundings. An adaptation is a feature that allows an organism to better survive in its environment.

The Theory of Evolution by Natural Selection

Charles Darwin challenged traditional views of a young Earth inhabited my unchanging species. In 1859, Darwin published convincing evidence that the many species of organisms presently inhabiting Earth are descendants of ancestral species, that is, species evolve. Most importantly, Darwin proposed a reasonable mechanism explaining how species evolve by natural selection.

Darwin reasoned that populations in nature were also limited by factors such as food, water, shelter, disease, and predation, and organisms had more offspring than can ever survive.

A population is all the individuals of a species that live in an area.

The individuals in a population vary in their characteristics or traits. A variation is the difference in a physical trait of an individual from those of other individuals in the population. The individuals in a population are the same species, but they are not identical. Variation? ___________________Color and pattern

Example of Natural selection in jaguars. 11,000 years ago, jaguars faced extinction. Some jaguars in the population had larger jaws. Variation? ____________ Larger jaw

There were fewer of their usual prey, mammals. There was an abundance of shelled reptiles. Those jaguars with larger jaws were able to eat the shelled reptiles. Favorable variation? ___________ Larger jaw

If the variation allows the individual to better survive in its environment, then we call that variation an adaptation. The individual is better adapted to its environment. An adaptation is any heritable characteristic that increases an organism’s ability to survive and reproduce in its environment. Adaptation in the jaguars? ____________ Larger jaw

Individuals with the adaptation have greater fitness. Fitness describes how well an organism can survive and reproduce in its environment.

Individuals with the adaptation will be able to eat more, and produce more offspring. The adaptation will be inherited by its offspring, making the offspring better adapted to the environment. The offspring will eat more, reproduce more offspring, and pass its adaptation/genes to its offspring.

The jaguars with larger jaws survived, and reproduce more offspring. Their offspring inherited the larger jaws and they survived and produced more offspring.

Eventually, the population will consists only of individuals with the adaptation. More and more individuals in the population will have the new adaption. In time, the number of individuals that carry the favorable adaptation will increase in the population. Simultaneously, individuals that do not have the adaptation will die, or produce fewer offspring. Evolution has occurred. The nature of the population has changed.

Larger jaws became a more common trait in the population. Over many generations, jaguars evolved larger jaws.

Darwin further suggested that organisms differ from place to place because their habitats present different challenges to survival and reproduction. Each species has accumulated adaptations in response to its particular environment resulting in evolution of the species.

Natural selection is a mechanism by which individuals that have inherited beneficial adaptations produce more offspring on average than do other individuals.

Darwin’s Theory Darwin’s theory of evolution by natural selection is supported by four major points

This leads to a struggle for existence (competition) among individuals of a population, with only a small fraction of their offspring surviving each generation. 1. Overproduction & Struggle for Existence Individuals produce more offspring than the environment can support.

2. Variation and Adaptation Members of a population vary extensively in their traits. This variation is heritable. Some variations or adaptations make an organism better suited to its environment and increase an organism’s chance of survival and reproduction.

3. Survival of the Fittest The individuals that have the greatest fitness survive and reproduce more offspring. Individuals with low fitness die before reproducing or reproduce few offspring.

4. Natural Selection Over generations, the individuals with the adaptation tend to accumulate in the population. Natural selection will result in species with adaptations that are well suited for survival and reproduction in an environment.

EVIDENCE OF EVOLUTION

Fossils provide evidence that Earth is very old…4.6 billion years old Life is very old…3.5 billion years old Life on Earth has changed…evolved

Fossils show a pattern of development from early ancestors to modern descendants.

Fossils offer the most direct evidence that evolution takes place.

Comparative Embryology Development of embryos tell an evolutionary story – Very different animals have similar structures during development At an early stage of development, all vertebrate embryos have “gill slits” At an early stage of development, all vertebrate embryos have “gill slits” Very different animals! But they share a common ancestor Develop into gills develop into structures of ear and throat.

During early stages of development, all vertebrate embryos have a tail. LizardTortoisePigHuman Why? We share a common ancestor!

The similar features of embryos in very different organisms suggest evolution from a distant common ancestor. FishHuman We share a common ancestor! Very similar!!!

Comparisons of the anatomy of different types of organisms often reveal basic similarities in body structures even though the structure’s functions may differ between organisms. Anatomy

Homologous Structures Sometimes very different animals have very similar arrangement of bones. – limbs that perform very different functions are built from the same kinds of bones. WHY?

Homologous structures are similar structures that appear in different organisms and have different functions. These very different animals share a common ancestor. --- As different groups of vertebrates evolved, their bodies evolved differently. --- But similarities in bone structure can still be seen. Homologous structures provide evidence of a common ancestor.

It would be unlikely for many species to have such similar anatomy if each species evolved independently.

Some organisms have similar structures, however, they are not closely related. Some structures found in different species have the same functions but they did not evolve from a common ancestor. The wings of bats and insects are analogous structures.

Analogous structures are structures that perform a similar function, such as flight, but did not evolve form a common ancestor. These two organisms have similar needs caused by the environment, so they evolved similar structures. They do not share a common ancestor. They both had a need to ____, so they evolved ______ independently.flywings

Lion Pelvis What is one function of the pelvis? _________________ Aids in locomotion

Some organisms have structures that seem to lack any useful function, or are no longer used for their original purpose.

Vestigial structure is a remnant of a structure that served an important function in the organism’s ancestor. Vestigial Structures Why do whales and snakes have a vestigial pelvis?

Whales evolved from terrestrial ancestors with four legs. Snakes evolved from lizards with four legs. The human appendix is a vestigial structure, reduced from the cecum of primate ancestors, which was involved in digestion of significant plant material.

The whale’s missing link Hind leg bones on a whale fossil Vestigial Structure

amino acid amino acid amino acid amino acid amino acid amino acid amino acid amino acid amino acid amino acid amino acid amino acid Protein A in Humans amino acid amino acid amino acid amino acid amino acid amino acid Protein A’ in Chimps Protein A ‘’ in Lemurs One amino acid difference Humans and Chimps are closely related Proteins: Species that share a more recent ancestor have fewer amino acid sequence differences. Biological Molecules

Proteins: Species that share a more recent ancestor have fewer amino acid sequence differences. amino acid amino acid amino acid amino acid amino acid amino acid amino acid amino acid amino acid amino acid amino acid amino acid Protein A in Humans amino acid amino acid amino acid amino acid amino acid amino acid Protein A’ in Chimps Protein A ‘’ in Lemurs Various amino acid differences Humans and Lemurs are distant relatives

Biological Molecules LampreyFrogBird Dog MacaqueHuman Comparing Protein Structure Number of amino acids different from human hemoglobin Number of amino acids different from human hemoglobin A B C D E Which organism is most closely related to humans? ______________ Organism A Which organism is the least related to humans? ______________ Organism E

DNA Sequences: Closely related species share a greater proportion of their DNA than do more distantly related species. Our DNA is approximately 95% identical to a chimpanzee’s DNA.

LET’S ALSO REMEMBER… All living things use the same genetic code! TTA codes for Leucine in bacteria as well as in human. The most logical explanation is that all species descended from a common ancestor.

TAIL What type of structure is it? homologous structure analogous structure vestigial structure mammal fish Not closely related

What are these bones an example of? __________________________ Structure of bones? ________________ Function of bones? ________________ very different very similar grasping flying walkingswimming Homologous structures Why are homologous structures important? ____________________________________ They provide evidence of a common ancestor…evolution.

Pelvic bones provide support for walking. Whales have a much reduced pelvic bones. This is an example of: Homologous structure Analogous structure Vestigial structure