EVOLUTION

Relationships Among Organisms

Similarities Among Organisms

All organisms on Earth are related

Some relationships are easier to see than others – though most organisms have some similarity in body structure

Similarities Among Organisms

Common Descent

Living things have slowly changed over time Each living species descended from other

species over time Principle of common descent – all living

things share common ancestors

Common Descent

Anatomists discovered that when comparing adult animals with four limbs, similarities exist among the bones of the various types of arms and legs

These are called homologous structures – have the same structure, but differ in function

Means they come from common origin

Common Descent

There are also embryological similarities

Discovered vestigial organs – structures that seem to serve little or no purpose

Similarities Among Organisms

Each species has a “tool kit” containing visible and invisible tools that perform essential survival functions

Tool kits are the result of millions of years of evolution by natural selection

It is easier to modify existing tool kits than to create entirely new ones

The Role of Chance

Random change in population is called genetic drift

Can be caused by migration, random mating differences

These are changes that have nothing to do with natural selection

The Birth of New Species

Speciation is the formation of new species. New population must change enough that

breeding cannot occur with original population

Genetic changes can be from mutations or natural selection, but must lead to reproductive isolation

The Birth of New Species

Usually, speciation in plants and animals occurs when two groups of individuals become geographically isolated

Darwin’s finches p. 251

The Pace of Evolution

Gradualism is the view that evolution occurs slowly and steadily over long periods of time

Punctuated equilibrium is the view that there are long periods of stability interrupted by episodes of rapid change.

The Pace of Evolution

Adaptive Radiation

When a new species evolves in a relatively short period of time, or when an organism or a group of organisms colonizes a new area where other species compete for life’s necessities

Results in a new tool kit Leads to homologous structures

Adaptive Radiation

Sometimes called divergent evolution

Convergent Evolution

Unrelated species may independently evolve superficial similarities because of adaptations to similar environments.

Example: bats and birds both fly Leads to analogous structures – similar in

appearance and function but develop from anatomically different parts

Homologous vs. Analogous

Homologous structures – similar structure, different function

Ex. arm of a human, wing of a bird

Analogous structures – similar function, different structure

Ex. bat wing, bird wing

Distant Relationships

Looking at homologous structures, fossils, embryological similarities can show evolutionary relationships

What about single celled organisms?

Molecular similarities

Molecular Unity

Many genes are shared by a wide range of organisms

The same 20 amino acids make all proteins All cells need ribosomes – almost identical

genes The more closely two organisms are related,

the more closely their genes resemble each other

Muscle Proteins – in Yeast!

Myosin is a protein found in muscle cells in animals – and yeast cells

Yeasts do not move, so why do they need myosin?

They use it to move products around within the cell