2.1 Section Objectives – page 35 Identify how natural selection can create new species. Today’s Objective: Can be found in the book: Pg

Section 15.2 Summary– pages Stabilizing selection is a natural selection that favors average individuals in a population. There are three different types of natural selection: stabilizing, directional, and disruptive. NATURAL SELECTION Middle sized Siberian Huskies are selected for Evolution will not occur

Stabilizing Selection Example: human birth weight. Babies of low weight lose heat more quickly and get ill from infectious disease more easily, whereas babies of large body weight are more difficult to deliver through the pelvis

Section 15.2 Summary– pages Directional selection occurs when natural selection favors one of the extreme variations of a trait. NATURAL SELECTION This type of selection can lead to rapid evolution of a population.

Examples: Directional Selection Peppered Moths: as the environment changes, so do the traits that are fit for the new environment. In the case of the moths, the forests changed from light to dark and selection moved in the direction of darker moths Antibiotic Resistance Pesticide Resistance

Section 15.2 Summary– pages In disruptive selection, individuals with either extreme of a trait’s variation are selected for. NATURAL SELECTION This results in eventually having no intermediate form of a trait, and leading to two separate species.

What type of selection? Tortoise neck length –Short grasses, for short-necked tortoises –Tall grasses, for long-necked tortoises –No grasses for average-necked tortoises, so over time, they are selected against Disruptive Selection

What type of selection? Lizard body size: –Large lizards are easily seen by predators, but smaller lizards cannot run as fast to escape the predators –Mid sized lizards are most fit in the environment, so they survive and reproduce more often, changing the allele frequencies in the population

What type of selection? Anteater tongue length: –Anteaters with long tongues are most fit because of the depth of the nests of the termites they eat.

So…what is a species? –A population whose members can interbreed & produce viable, fertile offspring –Being reproductively compatible is a key component Western Meadowlark Sturnella magna Eastern Meadowlark Sturnella neglecta Distinct species: songs & behaviors are different enough to prevent interbreeding

Section 15.2 Summary– pages The evolution of new species, a process called speciation. This occurs when members of similar populations change so much from each other that they no longer interbreed to produce fertile offspring. SPECIATION

Section 15.2 Summary– pages In nature, physical barriers can break large populations into smaller ones. Geographic isolation occurs whenever a physical barrier divides a population and over time they change and become two different species. SPECIATION

Section 15.2 Summary– pages SPECIATION

Section 15.2 Summary– pages SPECIATION

Section 15.2 Summary– pages SPECIATION

Section 15.1 Summary – pages Most of the evidence for evolution is indirect, coming from sources such as fossils and studies of anatomy, embryology, and biochemistry. EVIDENCE

Scientists believe that the fact that ALL LIVING THINGS have A,T,C, and G in their DNA and all use the same coding for proteins means we are all related in some way. BIOCHEMISTRY

Anatomical evidence One form of evidence in the unity of life…..

Science sees structural similarities as evidence that organisms evolved from a common ancestor. Structural features with a common evolutionary origin are called homologous structures. Homologous parts are similar in structure, but may be very different in specific function. Whale forelimb Crocodile forelimb Bird wing

The body parts of organisms that do not have a common evolutionary origin but are similar in function are called analogous structures. Analogous parts are very different in structure, but perform similar functions.

Section 15.1 Summary – pages Vestigial structure—a body structure in a present-day organism that no longer serves its original purpose, but was probably useful to an ancestor. ANATOMY Video clip

Section 15.1 Summary – pages An embryo is the earliest stage of growth and development of both plants and animals. Embryos of different species have similar pharyngeal pouches and tails. EMBRYOLOGY

Section 15.1 Summary – pages Scientists believe the shared features in the young embryos of different species suggest evolution from a distant, common ancestor. Fish ReptileBirdMammal Pharyngeal pouches Pharyngeal pouches Tail EMBRYOLOGY

ChickenTurtle Rat