Unit 1: Introduction to Evolution

Adaptations

Living organisms adapt to their environments

Ex. Blue footed booby is adapted to life at sea

Adaptation Definition

An inherited characteristic

Enhances an organism's ability to survive and reproduce

In a particular environment

- Key factor in species survival

Darwin's Theory of Evolution

Darwin and Alfred Russell Wallace independently developed what we now call the theory of evolution

-Darwin received most of the credit, he did most of the development work

- Not a new idea in their time
- Ideas about how species change over time had been around long before Darwin and Wallace

Before Darwin

The study of fossils suggested species had changed over time

People knew:
- Earth was very old
- Present day species developed from ancestrial species
- By some natural process

Didn't know:
- How this happened
- What made it happen

Jean Baptiste Lamarck

Before Darwin, he suggested that life forms evolved

Lamarack's Proposed Mechanisms:
- Use and disuse
- Inheritance of acquired characteristics

Not well supported data

Sea Voyage

Helped Darwin crystalize his theory of evolution

In 1859, Darwin published On the Origin of Species by Means of Natural Selection

- He presented a strong, logical explanation of what he called DESCENT WITH MODIFICATION
- What we now call evolution

Explanation of How

He suggested that DIFFERENTIAL SURVIVAL AND REPRODUCTION of individuals within a population lead to species becoming better adapted to the environment

Differential Survival and Reproduction

Organisms having traits that favor survival and reproduction tend to leave more offspring than those with less favorable traits

Darwin Observed

- Organisms produce more offspring than the environment can support

- Organisms vary in many traits (phenotype)

Darwin Reasoned

- Organisms having traits that favor survival and reproduction tend to leave more offspring than those with less favorable traits
- Differential Survival Reproduction
- Favorable traits accumulate in a population over time

Mechanism of Evolution

Darwin proposed natural selection as the mechanism of evolution

Environment acts as a "filter" or "sleeve"
- Organisms with traits better suited to the environment product more offspring
- Favorable traits amplified over time

Organisms with traits less suited to the environment produce fewer offspring
- Disfavored traits become less common over time

Hence the term, "natural selection"

Adaptive Evolution

Natural selection is the only mechanism that consistently leads to adaptive evolution

- Fitness: An individual's contribution to the genes of subsequent generations
- The fittest individuals are those that pass on the most genes to the next generation
- Those that leave the most offspring

- Current natural environment conditions determines what traits are the "fittest" for that environment
- As environment changes, fitness changes

Darwin Proposed

Darwin proposed natural selection as the mechanism of evolution

- Found convincing evidence in the results of artificial selection - selective breeding of domesticated plants and animals, and nature

Varieties or subspecies

Maladaptations

Produced in artificial selection, not in natural selection

Important Points

- Evolution is a science based explanation for how life appeared/developed on earth

- Individuals do not evolve, populations do

- Natural selection can affect only heritable traits
- Heritable traits cannot be passed onto offspring

- Evolution is random, not goal directed
- Does not lead to perfection
- Favorable traits vary as environments change
- Chance (random) occurrences influence evolutionary trajectories

Traits

Individuals either have the trait or they do not (genome)

Natural selection picks individuals with favored traits in population to use

Phenotype

The expression of the genotype

Evolution is Not Goal Oriented

Ex. By influencing available food sources, climate change determined "winners" or "losers"

Support of Darwin's Theory

There is lots of scientific evidence that supports Darwin's scientific theory

- Scientific Support
- Evidence found in everyday life

Scientific Support

- The fossil record
- Biogeography
- Comparative anatomy
- Comparative embryology
- Molecular biology

Evidence in Everyday Life

- Pesticide resistant insect pests
- Multiple drug resistant pathogens
- New strains of food plants

Evolution Occur Today

Ex. Killer microbes evolve from harmless ones all the time

Fossils

Fossils show us that organisms have evolved in an orderly, historical sequence

Oldest known fossils are 3.2 BYA prokaryotic cells

BYA

Billion years ago

MYA

Million years ago

Oldest Eukaryotic Fossil

Tappania - unicellular eukaryote

2.1 BYA

Oldest Multicellular Fossils

Dickinsonia Cosata

600 BYA

Suggestions of Fossil Record

From "deep time" to the present, the fossil record suggests biodiversity and complexity steadily increased

The skull of homo erectus - 200,000 - 400,000 BCE

Many fossils link early extinct species with species living today

Fossil Intermediates

A series of fossil intermediates document the evolution of whales from a group of land mammals

Biogeography

Study of the geographic distribution of species - supports Darwin's theory

- Found by fossils and living organisms that are related

Homology

The similarity in characteristics that result from common ancestry

Comparative Anatomy

The comparison of body structures in different species

Homologous Structures

Similarity in structure and function resulting from common origin (common ancestry)
- Man's hand, cat paw, and bat wing (all mammals)

Analogous Structures

Similarity in structure and function resulting from different origin (non-common ancestry)
- Bat wing, bee wing, and bird wing

Comparative Embryology

The comparison of early stages of development among different organisms

Common embryonic structures reveal homologies

Ex. Chick embryo vs human embryo (human reabsorbs tail prior to birth)

Vestigial Organs

Historical remnants of structures that had important function in ancestors

Some homologous structures are vestigial organs

Ex. Pelvic and hind-leg bones of some modern whales or human appendix

"Not needed presently"

Molecular Biology

Comparisons of DNA and amino acid sequences among different organisms reveal evolutionary relationships

- All living things share a common genetic code for the proteins found in living cells

- We share genes from bacteria yeast, fruit flies, dogs, and chimpanzees

- The fewer the number of differences in the DNA (gene or nucleotide) sequences, the closer the common ancestor

Evolutionary Trees

Homologous structures and/or genes can be used to build evolutionary trees

The Weight of Evidence

Taken together:

- Many lines of evidence support Darwin's ideas as a valid scientific theory of life's origins

- Evolutionary theory has strong explanatory power

- This is why scientists find it useful

Two Flavors of Evolution

Macroevolution

Microevolution

Macroevolution

Specification over time

Examines mechanisms during evolution at the species/population level

Organisms

Microevolution

Changes in gene allele frequency over time

Examines mechanisms driving evolution at the genetic level

Genes