Darwin's theory of natural selection, its rivals, and cells Week 3 (finish ch 2 and start ch 3) 1
Historical context Discovery of the new world -new observations challenged long-held views -exposure to new plants and animals increased awareness of biodiversity Views like the fixity of species and a young Earth were disconfirmed -16-17th Europe became a scientific breeding ground paving the way for evolutionary thought. *Scientists were now trying to give better explanations to: -replace the disconfirmed ones -explain why biological organisms evolve 2
Racap of Darwin's theory of natural selection Natural selection -mechanism explaining evolutionary change -influenced by previous scientists and Darwin's observations. Summary of NS -there's always variation of heritable traits for all members of a species -traits are advantageous (increase reproductive success) relative to environmental context -advantageous traits accumulate over time resulting in new species. -new species can also arise due to geographic isolation. 3
Racap of Darwin's theory of natural selection Terms and concepts Reproductive success: number of offspring an individual can produce that live to be reproductively viable. Fitness: the relative measure of reproductive success. Selective pressures: forces in the environment influencing reproductive success. 4
Examples of natural selection: Galapagos finches -Local environmental conditions varied from island to island SO: NS led to different populations to diverge from each other *Differences between species = beak size and structure Heavy beaks = exploit seeds and leaves Long stout beaks = exploit insects in trees (like a woodpecker) Long thin beaks = exploit flying insects 5
NS ex: Antibiotic resistance in bacteria Recall: environmental pressures make certain variations do better than others. Environmental pressure: advent and extensive use of antibiotics Selection for: advantageous traits like higher resistance to antibiotics -Over many generations, a new resistant bacterial species emerges. 6
Conditions for NS to occur Examples highlight important conditions needed for natural selection i. NS only acts on heritable traits ii. NS only acts on already existing variation in heritable traits iii. Fitness is a relative measure that changes as the environment changes iv. NS only acts on traits that affect reproduction 7
Example 1: Dog breeding Q: How could you turn a pack of wolves into Chihuahuas? If you're given a pack of wolves to breed, how would you start breeding the wolves to eventually make a Chihuahua? Note: All dogs descended from wolves 8
Constraints on Darwin's theory of natural selection First constraint: Didn't know why biological variation occurs in all species. Second constraint: Didn't know how traits were inherited traits -Blending inheritance fails Much later, -advancements in scientific technology -advancements in cell biology and genetics -the rediscovery of Mendel's principles of inheritance...allowed us to overcome these constraints on Darwin's theory 9
Intelligent design is a terrible explanation Science is about explaining facts about the world we observe. No explanation should be excluded if it's a good explanation of such facts. Intelligent design (ID) claims the best explanation for biology is that it was designed by an intelligent being. ID isn't used in science because it's a terrible explanation. Here are the following best criticisms of ID. 10
ID is a terrible explanation because: 1. ID doesn't fit with our background experience of design 11
ID is a terrible explanation because 2. ID is uninformative We don't know the process the designer used to design things. We don't know the designer's intentions. 12
ID is a terrible explanation because 3. ID is unfalsifiable ID is so vague, no potential observation would falsify it. Saying: intelligent designer is still vague because intelligent people design simple, complex, efficient, costly, good, and poor things too! 13
ID is a terrible explanation because In sum: good scientific explanations fit with our background experience, are informative and falsifiable. ID has NONE of these characteristics of good explanations so it's not useful to discuss the scientific topics in physical anthropology 14
Natural selection, unlike ID, is a good explanation: 1. NS fits with our background experience NS fits with our background experience with artificial selection 15
Natural selection, unlike ID, is a good explanation: 2. NS is informative because NS uses known processes to explain how traits are transmitted across generations -ch 3 and 4 tells us about genetics and Mendelian principles of inheritance NS says traits are advantageous given the environmental context -fitness is relative to environmental pressures 16
Natural selection, unlike ID, is a good explanation: 3. NS is falsifiable New species only arise after many generations (Uniformitarianism). If we observe a species evolve into a new species in one generation, then this would falsify NS. 17
Chapter 3: Biological basis of life: genetics, cells, DNA 18
Constraints on Darwin's theory of natural selection First constraint: Didn't know why biological variation occurs in all species. Second constraint: Didn't know how traits were inherited traits 19
Genetics and cells Genetics studies how genes work and how traits are transmitted one generation to the next. -the constraints on Darwin's theory of natural selection were ultimately solved by findings of genetics Cells: the basic units of life -biology features single-celled organisms all the way to organisms like us which consist of trillions of cells 20
Cells: the most basic units of life *the earliest life arose 3.5 bya (bacteria and blue-green algae) *Eukaryotic cells arose 1.7 bya -the types of cells comprising multicellular organisms 21
Cell types Two cell types Somatic cells: the cellular components of bodily tissues Gametes: the sex cells (sperm and ova) -two gametes form a zygote 22
Cells: the most basic units of life Eukaryotic cells contain: organelles: substructures in cells which perform various functions *Organelles: nucleus, cytoplasm, ribosomes, and mitochondria Nucleus: houses the molecules that contain our genetic information: DNA (deoxyribonucleic acid) RNA (ribonucleic acid) Cytoplasm: surrounds a cell's organelles Ribosomes: manufactures proteins via protein synthesis Mitochondria: function in energy production and have their own DNA (mitochondrial DNA (mtdna)) 23
DNA DNA (deoxyribonucleic acid) - double-stranded host of the genetic code RNA (ribonucleic acid) - single-stranded molecule messenger (mrna) transfer (trna) DNA + RNA contain the genetic information controlling the cell's functions 24
DNA Structure Structure DNA is made of complementary chains of stacked nucleotides Nucleotides structure: composed of a sugar plus a phosphate (sides), and a nitrogenous base (rungs) Bases: form complementary bonds Adenine bonds with Thymine Guanine bonds with Cytosine 25
DNA Replication DNA can make multiple copies of itself to -key to growth and healing/repairing tissue -is needed for cell division Process of DNA replication 1. Enzymes 'unzip' bonds between the bases 2. Exposed bases attract complementary free-floating nucleotides 3. Two parental nucleotide chains are models for growing replicated strands -the new DNA molecules consist of an original and new strand 26
Genes Genes: sequences of DNA bases guiding protein synthesis, partial protein formation, or any function products (e.g., RNA) Human Genome -25,000 genes -90,000 proteins Regulatory genes: produce proteins influencing the activity of other genes Homeobox genes: direct development of body plan and body tissue segmentation Hox genes: important for development of spinal regions 27