Download Natural Selection

THE EVOLUTION OF LIFE
Chapter 26
26.1 The Origin of Life


Fossils suggest that life on earth is over 3.5 billion
years old.
Several hypotheses for origin of life:
 Primordial
soup
 Meteorites
 Mars
 Deep
sea environments
26.2 How Living Things Change Over Time

Fossils show us that life
has not always been
like it is now.
 Fossils
are ancestors of
modern species
Ex. Ancestor of a modern
horse.
26.2 continued

Jean Baptiste Lamarck (1744-1829) – French
scientist
 Modern
species are descendants of ancestors
 Have evolved – changed over time – to become better
suited to their environment.
 Acquired new characteristics and passed them on
Ex. Giraffes stretched neck and passed it on.
 Not correct – acquired traits are not passed on.
Ex. Weightlifter
Darwin and Natural Selection


Charles Darwin (1809-1882) – English scientist –
developed theory of evolution.
Published The Origin of Species by Means of Natural
Selection in 1859.
 Proposed
that evolution – inherited change over time –
had produced all living things on earth. Caused by:
 Natural Selection – organisms with advantageous traits
survive better
 Pass on advantageous traits to offspring.
 Advantageous traits become more common in population
Ex. Giraffes long neck
Lamarck vs. Darwin
26.3 The Key to Evolution: Natural Selection
and How It Works

1.
2.
3.
4.
This is how natural selection works:
Variation – traits that are different within a
population. Ex. Hair color
Heritability – variable traits that are determined
by genes – can be passed on.
Natural Selection – variable heritable traits that
are advantageous are passed on to offspring.
Adaptation – advantageous traits become more
common in the population. Population evolves to
become better adapted to its environment.
How Natural Selection Works
26.4 Adaptation


Adaptations – traits that make organisms good at
living and reproducing in their environment.
Types of adaptations:
 Survival
– organisms must obtain food and resources
and avoid predators.
 Acquire mates – coloring, sounds, size, strength, etc.
 Parental Care – natural selection favors organisms that
help offspring survive.
26.5 Genetics and Evolution
How does evolution affect the genes in a population?
 Allele frequencies – how common different alleles
are (%)
 Natural Selection acts on phenotype (traits), not
genotype (genes).
 Affects


genes, but doesn’t act directly on them.
Genetic Drift – the evolution of populations due to
chance. Ex. Storm wipes out a population
Heterozygote advantage – a situation where
heterozygotes do better than either homozygote.
26.5 continued
26.5 continued

Where variation comes from: - Variation is vital –
it gives a population a better chance of adapting
to a changing environment.
 Genetic
mutations account for variation
 Without it we’d still be bacteria!
26.6 How a New Species Forms


Species – a breeding population of organisms
Speciation – formation of a new species
 Results
from reproductive barriers.
 When two populations can no longer breed – they’re
now separate species.
 Some stop mating Ex. Courtship rituals, physical
limitations
 Mating might fail – sterile offspring. Ex. Mule, liger
26.6 continued

Geographic barriers physically separate
populations.
 Populations
evolve separately and become different
species.
Ex. Mountains, glaciers, rivers, oceans, canyons, land, etc.
26.7 Evidence of Evolution


1.
The theory of evolution has been tested repeatedly
against observations of the natural world and the
evidence for evolution is overwhelming!
Eight main kinds of evidence support the idea that
evolution produced the diversity of life on Earth.
Observations of Natural Selection – Ex.
Peppered moths in England.
2.
Artificial Selection – Humans artificially select for
desirable traits in animals and crops all the time.
 Humans
have caused distinct evolutionary changes in
organisms.
3.
4.
Vestigial Organs – not functional – remains of
organs found in ancestors. Ex. Snakes
Similarities in body structures – front limbs of
some mammals. Many different uses, but same
bone arrangement.
5.
6.
DNA of organisms – related species have similar
nucleotide sequences.
Development of organisms – related species
develop in similar ways.
7.
Fossils of organisms - show
how organisms have evolved
over time. Many fossils have
intermediate features.
8.
Biogeography – the study of where species are
found on Earth.
 Similar
species are generally found close to each other.
 Lots of flying animals on islands.
 Different species in The Arctic and Antarctica.
26.8 How Humans Evolved

Humans are primates. We belong to the same order
as monkeys and apes.
 This
does NOT mean we are descended from them. Just
that we are closely related to them.
 We belong to the family Hominid, the group Homo, and
the genus Sapiens. Homo Sapiens
 We are the only hominid species in existence today.