Evolution and Diversity of Life Module 4 Topics: Chapter 14: Origin of Life Chapter 15: Evidence and Theory Chapter 16: Populations & Species Chapter 17: Human Evolution Chapter 18: Classification
Chapter 14: Origins of Life • Biogenesis: “All living things (currently) come from other living things” • This seems reasonable, but has not always been accepted. At one time, spontaneous generation myths were widespread. • Spontaneous generation: The largely discredited belief that living things could easily arise from non living things. • These are now mostly considered myths, but it can be argued that spontaneous generation must have taken place at least once
Spontaneous Generation Myths • Can maggots be created from rotten meat? • Can rice grains turn into mice? • Can mud turn into fish? • Can broth turn into germs? • At one time people believed all of the above ideas. Today we know that these are just myths. • No careful observer has ever observed rice turning into mice. We now know maggots are actually baby flies, whose eggs were laid in the rotten meat.
Spontaneous Generation was Disproved by Experimentation • Francisco REDI’s Experiment • Proved maggots come from fly eggs. P.261 • Lazzaro SPALLANZANI’s Experiment • Showed micro-organisms do not grow in sealed jars (but excluded oxygen) P. 262 • Louis PASTEUR’s Experiment • Proved micro-organisms are carried in dirty air, not spontaneously generated (his experiment allowed clean air in) P. 263
Abiogenesis:Spontaneous Generation Once Long Ago • So how did life get here if spontaneous generation does not take place? • It must have happened once-upon-a-time! • Remember: The world 4 billion years ago was very different from what it is now. • Atmosphere then: Hydrogen (H2), Methane (CH4), Ammonia(NH3), Carbon dioxide(CO2), Water vapour • Atmosphere now: Nitrogen (≈78%), Oxygen (≈21%), Carbon dioxide (<1%), Water vapour (variable), Argon (trace)
Age of the Earth: • Big Bang: ≈13.7 billion years ago • Sun formed =5 or 6 billion years ago • Earth formed: ≈ 4.5 billion years ago • Earth cooled: ≈ 4.0 billion years ago • First Life formed: c. 3.2 to 3.8 billion years ago • Multicellular life: ≈ 500 million years ago • Reptiles ≈ 250 million years ago • End of dinosaurs ≈ 65 million years ago • Hominids > 3 million years ago
Ancient Earth • The world 4 billion years ago was very different from what it is now. • The atmosphere had more Hydrogen (H2), Methane (CH4), Ammonia(NH3), and Carbon dioxide(CO2) than it does now • The earth was warmer, with seas just below boiling • The weather more violent, with powerful thunderstorms
Oparin’s Hypothesis • In 1923 Alexander Oparin suggested that the conditions on early earth could give rise to organic compounds spontaneously. • To demonstrate Oparin’s hypothesis in 1953 two graduate students (Harold Urey & Stanley Miller ) built an apparatus containing the gases he believed were present in the early atmosphere Alexander Oparin Harold C. Stanley Urey Miller
Miller & Urey’s Device • They filled the bottom of their device with water, and heated it to simulate warm ancient oceans • They used a spark chamber to simulate lightning • After running this device for several weeks they discovered that they had produced several organic compounds, including amino acids
“Primordial Soup” • The main hypothesis coming from Miller and Urey’s experiment and Oparin’s original hypothesis is that the early Earth’s oceans filled with organic compounds, becoming a sort of primordial ooze, slime or soup. • Within this more concentrated organic soup, it was possible for the right arrangement of chemicals to come together to form a primitive form of life.
Alternate Theories • Some Biologists have suggested other mechanisms for making complex compounds, and variations on Oparin’s “Primordial Soup” hypothesis, including: • The organic compounds may have become even more concentrated in shallow pools along the ocean shore • Organic compounds could have come together in pores in rocky or sandy surfaces. • Life may have started in deep ocean hydrothermal vents. • Some organic compounds may have formed in space or on other planets, and been brought to Earth on meteorites. “There are those who believe life here began out there, far across the universe.” (I recall an old SF show that started with those exact words.)
Chapter 15: Theory and Evidence • In this chapter we will examine the evidence that life has changed over time. • We will look at several theories about how those changes have occurred.
Fossils A fossil is a trace of a long-dead organism
There are many types of fossils • Mold fossils are imprints, like footprints, and impressions of skin, feathers or bark • Cast fossils are made when the remains of ancient things are filled with minerals, like fossilized bones or petrified wood. • Fossils can also be preserved in amber (fossilized plant resin) or tar (a thick form of crude oil)
Who discovered fossils? • Fossils have been dug up for centuries. In ancient China some fossils were called “dragon bones” • The first European to realize that fossils were the remains of extinct animals was Robert Hooke (the same guy who first observed dead cells)
Layers of Fossils • In general, fossils exist buried in sedimentary rock layers laid down on the bottom of lakes, rivers and oceans long ago. • In general, the deeper the layer (or stratum) from which the fossil comes, the older the fossil is. • Some fossils can be dated by radioactive materials in them. Younger fossils Older fossils
The Eons of Time Eons Eras Periods (what was going on) The starting point for the Archean Eon has been set at varios points in this range Most now put it at about 3.8 billion years ago
Evolution • The idea that populations of organisms, and therefore species of organisms, change over long spans of time. Next Slide: The first theory of evolution.
Lamarck’s Theory of EvolutionJean Baptise Pierre Antoine de Monet Chevalier de Lamarck:The guy with the big name and the wrong idea!(Perhaps) • Lamarck first came up with a theory of evolution (c.1802) • Unfortunately his theory was wrong! • Lamarck believed that organisms could inherit “acquired characteristics” through use and disuse. • Lamarckian Myth: “If a giraffe stretches its neck to reach leaves all its life, it’s offspring will have longer necks.”
Lamarck’s reasoning… • It seems sensible at first glance: • Muscles that you use a lot grow larger, if you don’t use them they atrophy (get smaller) • It also makes sense that organs you don’t need should gradually disappear • Even some fossil record suggest that unused organs may get smaller or eventually vanish, (like human’s tail bone and appendix) • The problem with Lamarck’s idea is the mechanism he proposed. It doesn’t work!
Disproof of Lamarck’s Hypothesis • If the idea of use and disuse were correct, then preventing an organism from using a structure for several generations would cause that structure to atrophy (get smaller) • Experiments have pretty much disproven Lamarck’s hypothesis: • If you remove the tails of mice, they cannot use them. After several generations, mice with shorter tails should be born, but this does NOT actually happen. • Therefore, Lamarck’s main hypothesis is incorrect, which makes his whole theory very unlikely… But…
Perhaps Jean-Baptise Pierre Antoine de Monet Chevalier de Lamarck was a little bit right! NEW Optional Material • The recent science of epigenetics shows that conditions during your lifetime can switch genes on and off, and that some of these changes may be passed on to descendants. In biology, the term epigenetics refers to changes in phenotype (appearance) or gene expression caused by mechanisms other than changes in the underlying DNA sequence, hence the name epi- (Greek: over; above) -genetics. These changes may remain through celldivisions for the remainder of the cell's life and may also last for multiple generations. However, there is no change in the underlying DNA sequence of the organism; instead, non-genetic factors cause the organism's genes to behave (or "express themselves") differently.
Charles Darwin andAlfred Russel Wallace • In 1858 two different people (Darwin and Wallace) independently suggested a better theory of evolution. • Darwin published a more complete version of the theory the next year*, along with evidence he collected in the Galapagos Islands, so he is generally credited with the idea. * On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life, was published November 24, 1859. Title was later shortened to The Origin of Species.
Darwin’s Hypotheses • Descent with modification • Organisms change slowly over time. • Newer species are the modified descendants of older species. • Modification by Natural selection. • The main reason that gradual modifications occur is due to Natural Selection.
Natural Selection • The population of a species will increase exponentially, until some environmental factor limits it. • When there is a limiting factor, not all members of the species will survive to reproduce. • There is competition for food, space, mates etc. • Only the members who are successful competitors will survive to reproduce. • The genetic traits that allow an organism to survive are called its “fitness”. • The survivors are said to be “adapted” to the environment
The strength of Darwin’s Theory • Darwin’s theories of evolution have been rigorously examined for over 150 years. • Although many minor changes have been made to these theories to accommodate new discoveries, the two most basic of Darwin’s concepts continue to be valid: • 1) That species change over time. • 2) That the main cause of this change is natural selection.
Internal Evidence of Evolution(comes from studying the biology of organisms) • Homologous Structures: • Related organisms have structures that come from similar sources* , (eg flipper of a seal and hand of human) • Vestigial Structures: • Organisms have the remains of organs that serve little value at the present time (eg: human appendix and “tail bone”) • Similarities in Embryos: • The embryos of different organisms look very similar • “ontogeny recapitulates phylogeny” • Similarities in DNA and proteins: • Many organisms have similar biological chemicals • DNA similarity is so closely linked to evolution that it is now used trace the evolution of some organisms. *don’t mix homologous structures with analogous structures, which are similar in appearance but different in origin.
Haeckel’s Controversial “Ontogeny Recapitulates Phylogeny” Drawing Although many of Haekel’s ideas have been rejected by modern biologists as oversimplified, it is still a fascinating fact that the fetus of an organism shows evidence of its evolutionary ancestry.
External Evidence of Evolution(comes from studies of other areas of science) • The fossil record shows changes over time • The organisms of today are different from the fossils of the past • The older the fossils are, the more differences there are (in general). • Changes in populations of species have actually been observed in historic times. • Eg. Manchester Peppered Moths.
The Peppered Moths(Industrial Melanism) • 1848 peppered moth population near Manchester • 98% light mottled moths • 2% dark moths • 1895 • 5% light mottled moths • 95% dark moths Clearly, some type of evolution is at work here. In just 50 years a rare moth mutation has become the typical variety of moth.
Why ? • If you were a bird who ate moths, which of the moths in the picture below would you catch? You would probably catch the one that you can see. In 1848, most of the trees around Manchester were covered in light lichens, which camouflaged the more common coloured moths. Easy to see Harder to see
During the 50 years that followed 1848, the industrial revolution came to Manchester. The lichens died from pollution, and the trees became darker from soot. Now which moth would you spot? Easy to see Harder to see
Because the peppered moth population change can be cited as proof that evolution occurs, it has been very controversial. • Proponents use the extensive studies as proof that the changes in a population can occur as the result of natural selection. • Opponents point out that the photos I showed you were “staged”, therefore question if moths would ever naturally settle on oppositely coloured trees.
Patterns in Evolution • Coevolution • Two different organisms evolve in close relationship to each other. • Convergent Evolution • Several different species adapt to the same environment. Eventually they show similar features (but they never become the same species) • Divergent Evolution • AKA Adaptive Radiation. One species adapts to fit several different environments. Eventually it divides into different species.
Chapter 16: Evolution of Populations • In this chapter we will look at populations and how they vary and how they spread genes. • We will look at mutations, and the effect they have • We will study speciation, the development of new species.
Population Genetics • Population genetics is the study of evolution from a genetic point of view • A population is group of similar organisms
Variation • Within a population there is always variation. Some organisms are a bit taller or shorter, a bit faster or slower, a bit stronger or weaker, etc.
Causes of Variation • Environmental causes of variation • Better food, growth conditions • Injuries • Genetic causes of variation • Mutation (changes in genes) • Recombination (separation of genes in meiosis) • Random breeding and fertilization Not so important to evolution Very Important to Evolution.
Hardy-Weinberg Principle • Gene frequencies will not change if ALL of the following are true: • No mutations occur (no radiation or mutagens) • There is no migration (no one leaves or arrives) • Population is very large (ideally infinite) • Individuals mate randomly (no preferential mating) • Natural selection does not occur (no competition) • In other words, evolution would not happen in an ideal world.
In the Real World, Evolution Occurs • Mutations do happen • Changes occur to genes as the result of radiation, chemicals or random events • Migration does happen • Individuals arrive and leave populations, changing the genetic makeup of the population
Populations are finite in size • Small populations allow “genetic drift” to occur, as allele frequencies change. • Mating is not always random • Some animals compete for mates, or have rituals that determine who mates (eg. Only the alpha wolf mates) • Natural Selection does occur • There is competition for resources in most populations. The survivors are the ones who reproduce.
Types of Natural Selection • Stabilizing • Most survivors are similar. The average is favoured, unusual individuals seldom survive • Directional • Most survivors have a particular feature. Individuals without the feature seldom survive. • Disruptive • Either of two extremes is favoured. Average individuals seldom survive • Sexual • Mates are chosen by a particular feature. Individuals without the feature seldom reproduce.
Hominid Fossils • Humans and some of their extinct relatives belong to a family known as hominids. • Hominids are classed within the order primates, along with apes and monkeys. • The oldest hominid fossils have been found in Africa. “Lucy” a hominid fossil from About 3 million years ago
The complete classification of humans is: • Kingdom Animalia(animal kingdom) • Phylum Chordata(chordates have a notochord) • Subphylum Vertebrata (with proper backbone) • Superclass Tetrapoda (decendants of four-limbed vertebrates) • Class Mammalia(the mammals) • Subclass Theria (live-birth mammals), • infraclass Eutheria (placental mammals) • Order Primates(the primates: monkeys, apes, hominids) • Superfamily Hominoidae (anthropoids, greater apes) • Family Hominidae(the hominids: humanlike. All other hominids except humans are now extinct) • Genus Homo(Humans and early humans) • Species sapiens(Modern “wise” humans) This is presented for your information. You don’t need to copy or memorize it