Change over TimePages 104 - 111

All of these frogs live in the same area. What differences are there?

Differences among organisms

• Each organism has a different adaptation to help it survive.

• Adaptation – a characteristic that helps an organism survive and reproduce in its environment– Examples: structures to find food, protection, or

moving from place to place.

Species

• A group of organisms that can mate with one another to produce fertile offspring.

• Ex: giraffe, lion, rhino

Species over time

• The Earth is a very old planet that scientists estimate to be 4.6 Billion years old.

• Life has existed on this planet almost as long.• Living things have changed with time.• Some died, some survived,

and some changed.• What caused the change?

Evolution

• The process by which populations accumulate inherited changes over time.

• Because of evolution, scientists believe all living things come from a common ancestor.

Evolution Evidence

• The largest piece of evidence for evolution is the fossil record.

• Fossils – the solidified remains or imprints of once-living organisms

• Fossils are made when an organism dies or leaves an imprint that gets covered by sediment layers.

Fossil Record

• The fossil record supplies evidence about the order in which evolutionary changes have occurred.

• Older fossils are found in deeper layers, while newerfossils are found in layers near the surface.

Gaps in the Fossil Record

• We do not have a complete fossil record of all organisms.

• Fossils are rare and not easily preserved.• Conditions for making fossils are not always

present.

Human skull shape

Vestigial structures

• The remnants of once useful structures.• Ex: Whales– Whales are mammals that need air to breath– Why are they living in the water?– There are remnants of what used to be hip bones

and leg bones in whales today– Whales might have ancestors that walked on land

Whale Evolution

More Evidence

• If we look at similar structures on different organisms, we see how similar the structures are.

• Humans, cats, dolphins and bats come from a common ancestor

DNA Comparison• With the development of genetic engineering,

we are able to look at DNA from several species and compare how similar they are.

• All organisms share some genetic material.• Scientists look at matching sequences of base

pairs• Ex: Chimpanzees and gorillas are close

relatives, while chimpanzees and turtles are distant relatives.

Comparing Embryonic Structures

• Early in development of any species, an individual goes through embryonic stages.

• In the early stages, organisms with a common ancestor look very similar.

• As organisms grow, they develop the features that make them different.