How Traits Change Over Time

How man has changed the traits of organisms through

Selective Breeding. Dogs have been breed to be friendly

Cows to produce more milk

Horses for speed

Gold-colored fish

Cats which are smalland not aggressive and can play

the piano?

If you wished to breed the prettiest guppies, how would you do it?

By only selecting the most colorful guppies and those with the longest tails, then breeding them generation after generation.

Wild guppies Guppy which has been selectively bred.

Dog breeders have been selectively breeding for desirable traits for centuries.

Farmers have cultivated many popular vegetables from wild mustard,

by artificially selecting for certain attributes.

Selective Breeding • nature provides variation, humans select

variations of genes that are useful.

• Example - a farmer breeds only his best livestock

In essence, when humans selectively breed organisms for certain traits, they are selecting for certain genes.

Charles Darwin (1809-1882) Sailed around the world 1831-1836

What did Darwin’s Travels reveal

• The diversity of living species was far greater than anyone had previously known!!

How did tortoises and birds differ among the islands of the

Galapagos?

• Each island had its own type of tortoises and birds that were clearly different from other islands

Galapagos Turtles

Natural Selection

• The traits that help an organism survive in a particular environment are “selected” in natural selection

He wondered if nature could select

for certain traits in the same way that man selects for certain traits.

Can you find the animals in the pictures below?

Observations

• Organisms produce many more offspring than can possibly survive in nature.

• Example- salmon typically lay ~10,000 eggs

• Only a few will survive to adulthood and reproduce.

Natural Selection

Organisms vary and

these variations (genes) are inherited by their

offspring.

Thousands of frog eggs are laid in clumps in a fresh water pond. Each clump is laid by one female. Few will survive to adulthood.

Apple trees produce far more seeds than could possibly survive to become full grown trees.

•As resources become scarce, individuals must compete with each other to survive.

•Most organisms will not make it to adulthood

•Very few will breed and pass on their genes.

Putting these facts together, Darwin discovered one of the most important ideas in biology--

Natural Selection.

• Offspring that do survive are best adapted to their environment

• They will pass their genes on to their offspring. • Over time, populations of organisms become

better adapted to their environment by this process of natural selection.

For example, this species of insect is well For example, this species of insect is well adapted (carries the right genes) to blend into its adapted (carries the right genes) to blend into its

environment.environment.

Do you see the walking stick insect?

It received those genes from its parents, whose genes It received those genes from its parents, whose genes were successful enough to allow them to survive were successful enough to allow them to survive

long enough to breed.long enough to breed.

Another example of natural selection at work

(click below to watch video clip)

Note: Turn caption on while viewing

Populations are constantly changing

(The Eternal Arms Race)

Click on the video below to see an interesting case of an evolving arms race.

Evolution means change over time.

Cars have changed over time.

Computers have changed over time.

Video games have changed over time.

pong

Primate Brain

Capacity

Vestigial Organs

• Traces of homologous organs in other species

• Organ that serves no useful functione.g. Appendix , wisdom teeth

Natural Selection (in summary)

1. Organisms vary and these variations (genes) are inherited by their offspring.

2. Organisms produce more offspring than can possibly survive in nature.

1. Those offspring that do survive are best adapted to their environment and will pass their genes on to their offspring.

The result is, over time, populations of organisms become better adapted to their environment by this process of natural selection which increases their survival rate .