Alfred Russel Wallace
- Alfred Russel Wallace independently developed the theory of natural selection at the same time as Darwin.
- Darwin usually gets more credit, although Darwin was a co-author of evolution.
- Wallace did a lot of work studying warning colouration as evidence for evolution through natural selection.
→ For example, wasps and snakes.
Extinctions
- This occurs when the last living member of a species has died.
- Evolution, natural disasters, climate change, and hunting can all cause species to become extinct.
- We know there have been five mass extinctions in the past 500 million years, according to fossil records.
- Some scientists believe we're on the verge of a sixth mass extinction.
- A lot of pollution and climate change caused by humans.
- Some species can become extinct if an invasive species is introduced from another place and outcompetes a native species; e.g., red and grey squirrels and American crayfish.
- Bees are essential to humans. Without them, crops wouldn't be pollinated, and we'd have no food, and humans would go extinct.
- Resistant Rats: Rats are now resistant to warfarin poison. Lots of rats and pests can be killed with it, as it's a selection pressure that causes a mutation (selective advantage) for rats to be resistant to warfarin. It happens because of natural selection.
The Five Kingdoms
Animals:
- Eukaryotic
- Multicellular
- Heterotrophs (eat/consume)
- Usually able to move around.
Plants:
- Eukaryotic
- Multicellular
- Cellulose cell walls and contain chlorophyll.
- Autotrophic (makes own food)
Fungi:
- Eukaryotic
- Single-celled (yeasts) or multicellular
- Chitin cell walls
- Then there is mycelium, consisting of hyphae.
- Saprotrophic (eats through extracellular digestion)
Protista (rubbish bin kingdom):
- Eukaryotic
- E.g., protozoa/seaweed
- Single-celled or multicellular
- Show a wide variety of forms
- Can be plant-like or animal-like
Prokaryotes:
- No nucleus
- No membrane-bound organelles
- Loop of DNA and plasmids
- Smaller than eukaryotic cells
Classification
- Classification makes organisms easier to study.
- It organises living things into groups.
Artificial Classification:
- Early attempts at classification only used observable characteristics to group organisms according to their similarities and differences.
- This doesn't reflect the relationships between species.
→ For instance, a wildflower identification book groups all yellow flowers on plants together.
Carl Linnaeus:
- A Swedish scientist developed a universal classification system known as the taxonomic system, which is still in use today.
- The top-level (biggest group) contains the five kingdoms.
- Kingdoms can be further divided:
Evolutionary Trees
- As science has advanced, natural classification has become more important.
- This classifies organisms according to their evolutionary history and their true relationships.
→ A sequence of DNA changes slowly over time, reflecting evolution.
- Evolutionary trees, which show how scientists believe organisms evolved over time and how closely related species are, can represent natural classification.
E.g.
- The evidence for natural classification comes mainly from DNA sequences but also from protein analysis and sequencing.
- Phylogenetics: Studying the evolutionary history of an organism.
- The taxonomic system is undergoing species reclassification.
→ The use of phylogeny studies and DNA analysis can lead to evolution and classification; a new level has been added to the existing hierarchy in 1990.
→ This new level contains 3 domains which are bigger groups than kingdoms: four out of 5 kingdoms are eubacteria and the other one (prokaryotes) is split between bacteria and archaea.
- Convergent evolution: Evolution that makes species look similar even though they're only very distantly related.
→ E.g., sharks and dolphins.