THE THEORY OF NATURAL SELECTION

Chapter 13 Section 1

Grade 10 BiologySpring 2011

Objectives

Identify several observations that led Darwin to conclude that species evolve

Relate the process of natural selection to its outcome

Summarize the main points of Darwin’s theory of evolution by natural selection as it is stated today

Contrast the gradualism and punctuated equilibrium models of evolution

Bell Ringer

Write down what you already know about evolution

Biography of Darwin

Darwin was a poor student, disinterested in subjects his father wanted him to engage in

Attended medical school but was repelled by surgeries and often skipped lectures

Was often found outdoors collecting biological specimens

Completed a degree in theology but was interested in natural sciences

Biography of Darwin

In 1831, Darwin was recommended for a position as a naturalist on the HMS Beagle

Science Before Darwin

Idea that each species is a divine creation that exists, unchanging, as it was originally created

Scientists had begun to seek to explain the origins of fossils Tried to explain their observations by altering

traditional explanations of creation Others proposed various mechanisms to explain how

living things change over time

Science Before Darwin

Lamarck’s theory Over the lifetime of an individual, physical features

increase in size because of use or reduce in size because of disuse

These changes are then passed on to offspring Is incorrect, but correctly pointed out that change in

species is linked to “physical condition of life”

Darwin’s Observations

Read Lyell’s book Principals of Geology, that proposed that the surface of the Earth changed slowly over many years

Visited different places, where he saw things that he thought could be explained only by a process of gradual change Extinct Armadillo fossils similar but not identical to

present species

Darwin’s Observations

Galapagos Islands Many plants and animals resembled those of coast Hypothesized that ancestors of Galapagos species

migrated to islands from South America long ago and changed after they arrived Called it decent with modification- evolution

Growth of Populations

Malthus Wrote that human populations are able to increase

faster than the food supply can Unchecked populations grow by geometric

progression Food supplies grow by arithmetic progression Proposed human population do not grow unchecked

because death caused by disease, war, and famine slows population growth

Growth of Populations

Population: consists of all the individuals of a species that live in a specific geographical area and that can interbreed

Evolution by Natural Selection

Darwin realized Malthus’s hypothesis about human population applied to all species

Every organism has potential to produce many offspring during its lifetime

In most cases, only a limited number of offspring survive to reproduce

Evolution by Natural Selection

Darwin connected Malthus’s ideas with his own observations and ideas

Individuals that have physical or behavioral traits that better suit their environment are more likely to survive and will reproduce more successfully than those that do not have such traits Natural Selection

Natural Selection

Evolution by Natural Selection

In time, the number of individuals that carry favorable characteristics that are also inherited will increase in a population Nature of population will change- evolution

Evolution by Natural Selection

Proposed organisms differ from place to place because their habitats present different challenges to and opportunities for survival and reproduction

Adaptation: is an inherited trait that has become common in a population because that trait provides a selective advantage

Publication of Darwin’s Work

1844, Darwin wrote down his ideas about evolution and natural selection

Published in 1858 Presented with Alfred

Wallace who was coming to the same conclusion as Darwin was about natural selection and evolution

Darwin’s Theory

1. Inherited variation exists within the genes of every population or species (the result of random mutation and translation errors)

2. In a particular environment, some individuals of a population or species are better suited to survive (as a result of variation and have more offspring- natural selection)

Darwin’s Theory

3. Over time, the traits that make certain individuals of a population able to survive and reproduce tend to spread in that population

4. There is overwhelming evidence from fossils and many other sources that living species evolved from organisms that are extinct

Darwin’s Ideas Updated

Change Within Populations: Now know genes are responsible for inherited traits Certain forms of a trait become more common in a

population because more individuals in the population carry the alleles for those forms

Natural selection causes the frequency of certain alleles in a population to increase or decrease over time

Mutations and recombination of alleles that occurs during sexual reproduction provide endless sources of new variations of natural selection to act upon

Darwin’s Ideas Updated

Species Formation: The environment differs from place to

place Populations of the same species living in

different locations tend to evolve in different directions

Reproductive isolation: condition in which two populations of the same species do not breed with one another because of geographic separation, difference in mating periods, or other barriers to reproduction May eventually become unable to breed

together

Darwin’s Ideas Updated

The Tempo of Evolution: Gradualism: model of evolution in which gradual

change over a long period of time leads to species formation

Suggested that successful species may stay unchanged for long periods of time (Gould and Eldredge)

Major environmental events in the past have caused major evolution to occur in spurts

Punctuated equilibrium: model of evolution, in which periods of rapid change in species are separated by periods of little or no change

Evidence for both

Review

1. T/F Malthus and Lyell influenced Darwin in his ideas of natural selection

2. T/F The number of individuals that carry favorable characteristics that are also inherited will increase in a population

3. T/F The smallest scale that evolution happens on is the individual

Answers

1. T/F Malthus and Lyell influenced Darwin in his ideas of natural selection

2. T/F The number of individuals that carry favorable characteristics that are also inherited will increase in a population

3. T/F The smallest scale that evolution happens on is the individual

Smallest scale is at the population level, individuals don’t evolve, populations do