Chapter 15Evolution

Important Vocabulary

1. Species: A group of organisms whose individuals can breed together to produce fertile offspring.

2. Population: A localized group of individuals belonging to the same species.

3. Evolution: A slow change in a population over time.

Slide # 2

Charles Darwin explained how Natural Selection could cause a population to adapt and change over time. (note he states- a “population” will change -not an “individual”)

Slide # 3

Charles Darwin: An Unlikely Evolutionist

1.Charles Darwina.1809: English born naturalistb.Went on a 5 year voyage on the

HMS Beagle as an unpaid scholar Collected plants & animals

during journeyc. Darwin did not set out to develop

a theory of evolutiond.Observations and specimens

collected helped Darwin formulate his theory of evolution.

Charles Darwin

Slide # 8

Darwin’s Observations on the Galapagos Islands

1.Fewer types of organisms on the islands

2.Island species differ from mainland species & from island to island

3.Finches on Galapagos resemble mainland finch, but there were more types on the islands

Slide # 11

Pinta IslandIntermediate shell

Pinta

Isabela IslandDome-shaped shell

Hood IslandSaddle-backed shellHoodFloreana

Santa Fe

Santa Cruz

James

Marchena

Fernandina

Isabela

Tower

Giant Tortoises of the Galapagos Islands

Each island had a variation of tortoise; long & short neck corresponded to type of vegetation.

Slide # 12

Darwin explained Evolution by Natural Selection

1. 1859: Darwin published On the Origin of Speciesa. Proposed that natural selection was the

mechanism for evolution.• Individuals vary in one or more traits &

there can be slight differences in their ability to survive & reproduce.

b. Nature selects those individuals w/ favorable traits to leave more offspring that are better suited (FIT) for their environment.

c. Decent with modification occurs over time• Each living species has descended,

with changes, from other species over time

Slide # 13

Published 25 years after

Darwin wrote it!

Beaver

NORTH AMERICA

Muskrat

Capybara

SOUTH AMERICA

Coypu

Evidence that Supports Evolution: Geographic Distribution of Living

Species

Beaver

Muskrat

Beaver andMuskrat

Coypu

Capybara

Coypu andCapybara

1. Similar animals on each continent live in similar ecological conditions

a. They were exposed to similar pressures of natural selection.

b. Because of similar selection pressures, different animals ended up evolving similar characteristics

Slide # 15

Evidence that Supports Evolution: Homologous Structures

1. Homologous structures: similar structures but different functionsa. Structures develop from same

clump of embryonic cellsb. Provides evidence that four-limbed

vertebrates descended from a common ancestor.

2. Vestigial structures: structures or organs that are reduced in size; do not seem to serve a useful function

3. Homologous & vestigial structures imply that common genes are involved.

Slide # 16

Homologous structures: forelimbs of vertebrates

Pelvis & femur bones are vestigial in whales

Evidence that Supports Evolution: Similarities in Embryology

1. The embryos of vertebrates are very similar during early development.

2. The same groups of embryonic cells develop in the same order and in similar patterns to produce tissues & organs.

3. Common cells & tissues growing in similar ways produce homologous structures.

4. Implies that common genes are involved.

Slide # 17

Embryos of vertebrates develop gill slits and tails.