1. THE EVOLUTION OF LIFE Chapter 26

2. 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

3. 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.

4. 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

5. 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

6. Lamarck vs. Darwin

7. 26.3 The Key to Evolution: Natural Selection and How It Works  This is how natural selection works: 1. Variation – traits that are different within a population. Ex. Hair color 2. Heritability – variable traits that are determined by genes – can be passed on. 3. Natural Selection – variable heritable traits that are advantageous are passed on to offspring. 4. Adaptation – advantageous traits become more common in the population. Population evolves to become better adapted to its environment.

8. How Natural Selection Works

10. 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.

11. 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.

12. 26.5 continued

13.  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!

14. 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

15. 26.6 continued  Geographic barriers physically separate populations.  Populations evolve separately and become different species. Ex. Mountains, glaciers, rivers, oceans, canyons, land, etc.

16. 26.7 Evidence of Evolution  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. 1. Observations of Natural Selection – Ex. Peppered moths in England.

17. 2. Artificial Selection – Humans artificially select for desirable traits in animals and crops all the time.  Humans have caused distinct evolutionary changes in organisms.

18. 3. Vestigial Organs – not functional – remains of organs found in ancestors. Ex. Snakes 4. Similarities in body structures – front limbs of some mammals. Many different uses, but same bone arrangement.

19. 5. DNA of organisms – related species have similar nucleotide sequences. 6. Development of organisms – related species develop in similar ways.

20. 7. Fossils of organisms - show how organisms have evolved over time. Many fossils have intermediate features.

21. 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.

22. 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.