HOW NATURAL SELECTION WORKS

EVOLUTION BY NATURAL SELECTION

How Natural Selection Works Selecting agents Any factor that affects the probability that a gene

will be passed to the next generation. Specific environment factors that favor certain

characteristics. Selecting agents could be: 1. Temperature of the environment 2.Sunlight 3. Wind speed 4.Toxic chemicals 5. Predation pressures 6. Humidity 7. Oxygen content in water

How Natural Selection Works

The two possible ways of how natural selection works.

1. Differential Survival 2. Differential Reproductive Rates

How Natural Selection Works

1. Differential Survival A population consists of a large

number of genetically different individuals.

Some of them possess characteristics that make their survival difficult.

They are likely to die earlier in life and not have an opportunity to pass their genes on to the next generation.

How Natural Selection Works

1. Differential Survival Example: English Pepper Moth.

How Natural Selection Works 2. Differential Reproductive Rates Survival does not always ensure

reproductive success. For a variety of reasons, some organisms

may be better at utilizing available resources to produce offspring.

Case in point: 1st individual – 100 offspring – passed more

genes. 2nd individual - <100 offspring – lesser

genes passed.

How Natural Selection Works

2. Differential Reproductive rates E.g. Clover plants

EVOLUTIONARY PATTERNS 1. DIVERGENT EVOLUTION A basic evolutionary pattern in which individual

events may cause many branches in the evolution of group of organisms.

Development of each individual species causes successive branches in the evolution of a group of organisms.

Higher levels of evolutionary change are the results of differences of accumulated over time,

Due to many selective factors that lead to greater and greater diversity.

Diversity leads to the evolution of new species.

EVOLUTIONARY PATTERN

A basic pattern in evolution of organisms is extinction.

Extinction is the gradual process by which a group of related organisms dies out.

Extinct species possessed specializations that made them at one time successful in their environments.

However the environment does not remain constant.

It often changes in such a way that the species that previously thrived are unable to adapt to the new set of conditions

EVOLUTIONARY PATTERN

All currently existing organisms will eventually become extinct.

Biologist must use a great deal of indirect evidence to piece together the series of evolutionary steps that lead to a current species.

E.g. Horse

EVOLUTIONARY PATTERN

2. ADAPTIVE RADIATION A specific evolutionary pattern in

which there is a rapid increase in the number of kinds of closely related species.

Evolutionary explosion of new species from a common ancestor.

EVOLUTIONARY PATTERN

2 SITAUTIONS THAT ARE THOUGHT TO FAVOR RADIATION

1. An organism invades a previously unexploited habitat.

2. A new type of organism evolves a new set of characteristics that enable it to displace organisms that previously filled niches in the environment.

E.g. Amphibians and Reptiles Darwin’s Finches

EVOLUTIONARY PATTERN

3. CONVERGENT EVOLUTION An evolutionary pattern in which

widely different organisms show similar characteristics.

Convergence in structure, type of food eaten, method of obtaining food.

E.g. Plants in desert environment Bats, Swallow and Dragonfly Whale, shark, tuna

RATES OF EVOLUTIONARY PATTERN

Rates of evolution can vary greatly. FACTORS THAT AFFECT RATE OF

EVOLUTION 1. Reproductive potential Reproductive potential influences how

quickly a population can respond to environmental changes.

E.g. Fruit flies – 2 week life cycle – 10 day period – 500 eggs

Elephant – 50 year lifespan – 4 offspring -

PATTERNS OF EVOLUTIONARY DIVERSITY

2. Rate of Environmental Change Selection is driven by the environment. If environment is changing rapidly, one

would expect rapid changes in the organisms present.

Also result in extensive episodes of extinction.

E.g. Little environmental change – slow

evolutionary change

PATTERNS OF EVOLUTIONARY CHANGE

1. GRADUALSIM The theory stating that evolution occurred

gradually with an accumulated series of changes over a long period of time.

Fossil record There were gradual changes in physical features

of organisms overtime. Accumulation of these changes could result in

such extensive changes from the original species, That we could consider the current organism to

be a different species from its ancestor. E.g. Charles Darwin’s view of evolution.

PATTERNS OF EVOLUTION 2. PUNCTUATED EQUILIBRIUM The theory stating that evolution occurs in

spurts, between which there are long periods with little evolutionary change.

In the fossil record some species seem to have appeared from nowhere.

It appeared suddenly and showed rapid change from the first time they first appeared.

Niles Eldredge and Jay Gould are the proponents.