Evolution and the Diversity of Life

Evolution and the Diversity of Life

Theory Theories embody the highest level

of certainty for comprehensive ideas in science. Thus, when someone claims that evolution is "just a theory," it's roughly equivalent to saying that the proposition that the Earth circles the sun rather than vice versa is "just a theory."

What is Evolution?

In the simplest biological terms evolution is defined as change over time. However, it is much more than that.

Darwin• Who was Charles Darwin?• Charles Darwin first published an

explanation of how species changed over time, or evolved.

• Darwin argued that modern-day species arose from ancestors

• Through a process of “descent with modification,” with natural selection as the mechanism.

5

Common Descent with Modification

• Darwin proposed that organisms descended from common ancestors

• Idea that organisms change with time, diverging from a common form

• Caused evolution of new species

6

Darwin’s Conclusion• Individuals who

inherit characteristics most fit for their environment are likely to leave more offspring than less fit individuals

• Called Natural Selection

How did he explain evolution?• Natural Selection: Occurs in natural

populations when organisms with certain traits pass those traits on to the next generation.

– Individuals with certain favorable inheritable traits produce more surviving offspring than others passing on that trait with more frequency

Natural Selection

• Natural selection is the mechanism for evolution.

• It only acts on populations.• It changes the frequency of

genes in a population – not in an individual.

9

Natural Selection

• Cannot Be Seen Directly• It Can Only Be Observed As

Changes In A Population Over Many Successive Generations–Radiation–Fossil Record

Peppered Moth Example• Originally White• Now more black than white• Causes

– Industrial Pollution• Soot covered trees

– Industrial Melanism

http://evolution.berkeley.edu/evolibrary/article//bergstrom_02

Change Over TimeChange Over TimeEvidence for evolution

1. Fossils2. Biogeography3. Compartive anatomy4. Embryology5. Biochemistry

Evidence for evolution1. Fossils2. Biogeography3. Compartive anatomy4. Embryology5. Biochemistry

• In biological terms a fossil can be defined as evidence of an organism that lived some time in the past.

• This gives an evolutionary picture of life on Earth and how species have changed over time.

• Also shows how organisms are related to each other

• Oldest fossils are in deepest layers/newest are in layers closer to surface

1. Fossils

Fossil Layers

14

15

Evidence for Evolution – The Fossil Record

• Is the study of the geographic distribution of species.

• First suggested to Darwin that today’s organisms evolved from ancestral forms.

2. Biogeography

Convergent and Divergent Evolution

• Divergent-Divergent evolution is the accumulation of differences between groups which can lead to the formation of new species. (ex; Darwin’s finches)

• Convergent– Convergent evolution describes the independent evolution of

similar features in species of different lineages. Convergent evolution creates analogous structures that have similar form or function, but that were not present in the last common ancestor of those groups

3. Comparative Anatomy

A. Homologous Structures – structural features with a common evolutionary origin – shared by related species.

Comparative Anatomy

B. Analogous Structures – Structural features which serve the same function in different species, but they evolved independently. Example: Butterfly wings, Bat wingsBird wings

Comparative Anatomy C. Vestigial Structures – structures

that were present in ancestor, but are reduced in modern species.

Humans have a vestigial tailbone.EX: Vestigial toes in the horse. Vestigial

limbs in whales and snakes.

3b. Structural Adaptations

A. Mimicry: A structural adaptation that protects an organism by copying the appearance of another species.

– Example: Gopher snake

B. Camouflage – A structural adaptation that allows an organism to blend in with its environment.

– Example: Snowshoe hare

Gopher Snakes?

The one on the left is a rattlesnake, the one on the right is a gopher snake.

Showshoe Hare

SummerWinter

Are ALL adaptations structural?

• No! Some adaptations are behavioral adaptations

• Moving in large groups is one example; it helps protect the members of the group from predators.

• Other types of behavioral adaptations:• Nocturnal • Arboreal• Burrowing

4. Comparative Embryology

Embryology – Early embryos of very different organisms closely resemble each other.

5. Molecular biology

Biochemistry – (DNA/genes) The greater the number of gene/DNA sequence similarities, the closer related the two organisms are.

5. Biochemistry

• Allelic Frequency – the percentage of any specific allele in the gene pool

• Genetic Equilibrium – frequency of alleles in a population remains the same over many generations

Changes in Genetic Equilibrium

• One mechanism for genetic change is mutation (radiation, chemicals, chance)

• Many mutations are lethal (do not survive) or null( not good or bad)

• Occasionally useful – new gene becomes part of the gene pool

Changes in Genetic Equilibrium

• Natural Selection is usually the most significant factor that causes changes in the gene pool

• Allelic frequencies change over generations due to natural selection of variations

Speciation

• Changes in the gene pool can lead to evolution of a new species over time

• Species = group of organisms that look alike and can interbreed to produce fertile offspring

• Speciation = evolution of a new species. Occurs when members of similar populations can no longer interbreed and produce offspring

Interbreeding Prevented By

• Geographic isolation• Reproductive isolation• Changes in chromosome number

Cladistics

• Cladistics: classification system in which organisms are grouped together based on whether or not they have one or more shared unique characteristics that come from the group's last common ancestor.

• Cladogram: A diagram used in cladistics which shows relations among organisms.

– http://www.youtube.com/watch?v=ouZ9zEkxGWg

Cladograms

35

OVERVIEW

• The Struggle for Existence (compete for food, mates, space, water, etc.)

• Survival of the Fittest (strongest able to survive and reproduce)

• Descent with Modification (new species arise from common ancestor replacing less fit species)