Darwin plus Modern Evolution

Evolution Lecture 1 Charles Darwin’s law or theory of Evolution has FOUR parts. Two parts were discovered by Darwin; and two parts were discovered by his successors. Most people who know of Darwin’s law are familiar with his idea of 1) NATURAL SELECTION. This is popularly known as “Survival of the Fittest .” It is the idea that Nature BREEDS all the different form of Life on Earth. “Natural selection is the differential longevity and reproduction of individuals due to differences in phenotype or bodily characteristics . It is the key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Charles Darwin popularised the term "natural selection", contrasting it with artificial selection or BREEDING , which is humanly intentional, whereas natural selection is not all intentional. Variation of traits, both genotypic and phenotypic, exists within all populations of organisms. However, some traits are more likely to facilitate survival and reproductive success. Thus, these traits are passed onto the next generation. These traits can also become more common within a population if the environment that favours these traits remain fixed. If new traits become more favored due to changes in a specific niche, microevolution occurs. If new traits become more favored due to changes in the broader environment, macroevolution occurs. Sometimes, new species can arise especially if these new traits are radically different from the traits possessed by their predecessors. The likelihood of these traits being 'selected' and passed down are determined by many factors. Some are likely to be passed down because they adapt well to their environments and live long lives . Others are passed down because these traits are actively preferred by mating partners, which is known as sexual selection. Female bodies also prefer traits that confer the lowest cost to their reproductive health or even bodily comfort which is known as fecundity selection.” ( https://en.wikipedia.org/wiki/Natural_selection ) Professor Brown: However, Darwin also found that 2) ALL LIFE IS RELATED TO ALL OTHER LIFE THROUGH COMMON ANCESTRAL SPECIES. This is the principle of PHYLOGENY as represented by a “THE TREE OF LIFE” diagram. ( See handout) “A phylogenetic tree, phylogeny or evolutionary tree is a graphical representation which shows the evolutionary history between a set of species or taxa during a specific time.[1][2] In other words, it is a branching diagram or a tree showing the evolutionary relationships among various biological species or other entities based upon similarities and differences in their physical or genetic characteristics. In evolutionary biology, all life on Earth is theoretically part of a single phylogenetic tree, indicating common ancestry. Phylogenetics is the study of phylogenetic trees. https://en.wikipedia.org/wiki/Phylogenetic_tree Darwin only had the above two theories; he _ lacked_ good theories of 3) what the mechanism of heredity was by which traits could be passed on from one generation to the next ; and 4) how variation in a species arose . He knew that bodily traits were inherited by children from parents, but he didn’t know how. He knew that there were different bodily traits within the populations of the same species, but he did not know how that variation was caused. Darwin’s successors solved theoretical problem 3) with the discovery of genes and DNA ; and 4) with the discovery of genetic mutations. These 2 theories combined with Darwin’s 2 theories of Phylogeny and Natural Selection form a complete Modern Evolutionary Theory ! (Charles Darwin : ( https://www.britannica.com/biography/Charles-Darwin ; https://www.youtube.com/watch?v=-NFfSLlCawE ; https://www.youtube.com/watch?v=-NFfSLlCawE ; https://iep.utm.edu/darwin/ ) (https://en.wikipedia.org/wiki/Evolution ) IMPORTANTLY, THE MEASURE OF DARWINIAN FITNESS/SUCCESSFUL ADAPTATION IS SPECIES POPULATION GROWTH; THE MEASURE OF UNFITNESS IS POPULATION SHRINKING , THE ULTIMATE UNFITNESS IS EXTINCTION !!! Please focus on this idea as it is not made explicit in standard presentations of Natural Selection. Please include this in your answer to the test question. The Darwinian Tree of Life represents COMMON ANCESTORAL relations between different species at nodes of branching on the Tree diagram .The Tree of Life diagram implies a timeline from bottom to top. Thereby it represents EVOLUTION by NATURAL SELECTION of new traits and retention of some old traits. The primate order is an order of the mammal class. All primates are mammals ; not all mammals are primates; increasingly inclusive categories as we go down on the Tree of Life . (( see handout of Primate Order section of Tree of Life) It was Darwin’s claim that all life is related through common ancestral species INCLUDING HUMANS (!) that was controversial (not so much Natural Selection), because it conflicted with the Christian doctrine of human origin by God’s creation in the Garden of Eden. In Darwin’s time, the idea that humans had evolved out of an earlier ancestor AT ALL was controversial. Darwin specifically hypothesized that the living species with the closest back in time or fewest generations back to a common ancestor with humans are chimpanzees; and that humans originated in Africa. Subsequently, investigating these two Darwinian hypotheses , paleotologist-scientists, including Raymond Dart, explored parts of Africa looking for fossil remains evidence of a so-called MISSING LINK species. The idea is links in a chain as representing a line of species , one link descending from the previous links. The “missing link” would connect humans to our common ancestor on the Tree of Life with chimps A fossil with characteristics constituting a link between a human “link” and a chimp “link” was discovered by Raymond Dart in Southern Africa (page 291 of text) ; and subsequently by many others . This proved Darwin’s hypothesis true. Dart found a fossil with a chimp sized brain BUT BI-PEDAL, OR HABITUALLY WALKING ON TWO FEET INSTEAD OF FOUR (quadrapedal). The phylogenetic-Tree of Life classification term for habitually bi-pedal primates is HOMININ. (See handout on Missing Link) ( https://www.britannica.com/biography/Raymond-A-Dart ) Modern Natural Science The modern scientific method of finding out truths about the world, the universe, originated 500 to 600 years ago in Europe. It has produced the estimates of the time of origin of major events of natural history of interest to this class as listed on the Scientific Cosmological or Worldview Timeline handout. The origin of life on Earth was approximately 3.6 billion years ago. The first life forms or species were single celled and cloned to reproduce. Cloning means an organism makes a copy of itself to produce the next generation. The origin of sexually reproducing species was approximately 1.2 billion years ago. Reproduction is necessary to perpetuate species because individual organisms are mortal. Dinosaurs’ origin approximately 240 million years ago and extinction 65 million years ago is an example of Darwin’s principle of NATURAL SELECTION against. There were other mass extinctions prior to the dinosaur mass ( many different species) extinction. ( https://www.britannica.com/science/life/Evolution-and-the-history-of-life-on-Earth ) The dinosaur extinction was (an example of Darwin’s concept of species being selected against) probably due to a comet or meteor striking and exploding like many , many nuclear bombs on the earth ; and throwing so much debris up into the atmosphere that it blocked much of the sun’s light for many, many years; and thereby killing much plant life that the food of the dinosaurs. (https://www.britannica.com/animal/dinosaur/Extinction ) Mammals ( we are mammals) lived simultaneously with dinosaurs. They were small , furry animals relative to dinosaurs, and the reduced amount of plant food was enough for their smaller bodies to survive the loss of plant life. Thus, mammals were SELECTED FOR in the Darwinian sense. Mammals were fit relative to dinosaurs; survival of the fit species. ( What Happened Immediately After the Dinosaurs Went Extinct ? Mammals ! https://www.youtube.com/watch?v=c7nyan0wnkQ ) Three characteristic traits of mammals are ,1) mammary glands to feed the young, 2) warmblood ,3) bodily fur. ( https://en.wikipedia.org/wiki/Mammal ). Primates, A PHYLOGENETIC ORDER OF MAMMALS, retain these 3 traits; and primates evolved stereoscopic vision (page 138 of text) as an adaptation to living in trees. This is not to be confused with the Tree of Life metaphor ; primates actually did live in trees. Stereoscopic vision, by way of eyes in front of the head forming almost parallel lines of sight , gives sharper vision at a distance. Thereby, primates didn’t fall of the trees to death , and could catch insects more exactly; in other words adaptation in the trees. (Chapter 7 of the text ; https://www.youtube.com/watch?v=BpnlS_ach-0 What is a Primate?) HOMININS Hominins (See last section of Chapter 12 and Chapters 13, 14 and 15 of the text _Physical Anthropology_) are distinguished from other primates by a skeleton adapted for bipedalism – the habit of _walking_ upright on the two hind limbs. Hominins in this class are habitually, anatomically, physiologically, naturally UPRIGHT-ERECT, BIPEDAL primates . Although, other primate species are able to stand on two legs temporarily , only hominins evolved as habitually bipeds. Kangaroos, some birds and other animals are bipeds , but they are not primates. https://www.britannica.com/science/bipedalism Some closely related primate species , including chimpanzees and gorillas, exhibit knuckle walking a pattern of movement in which long arms and the knuckles of the hand support the weight. See handouts There are several Darwinian natural selection hypotheses for the origin of bipedalism evolving out of a quadrupedal/knuckle-walking species ancestral to hominin species. 1) Adaptation to savanna ecological niche: Bipedalism may have allowed primates to move about more freely within savanna environments (grassland, with scattered trees, prevalent in Africa) and to watch out for predators over the tall grasses. Erect bipeds walk greater distance using less energy than quadrupeds can and , with their eyes elevated higher than quadrupeds can see over grasses and see a longer way into the distance for predators or prey. However, evidence from recent fossil finds suggests that early bipedal hominins lived in forested areas. 2) Bipedalism lessens stress from the extreme heat of the savanna in East and Southern Africa. The air is slightly cooler off the ground, and erect bipedalism exposes less surface area of the body to the midday sun.( page 311 of the text) 3) Carrying behavior: Bipedalism allows hominins to carry objects in the two front limbs (arms), enabling the carrying of food and easier transportation of the young ( fleeing predators or pursuing a nomad-migratory life way). Bipedalism also frees hands to carry tools and weapons. This Professor Brown’s football sports example. 4) The genitalia of both sexes are exposed to vision more in erect posture than in quadrupedal stooped posture. This may have resulted in more fertile matings by erect phenotype individuals (see page 311 text) 5) Other primates have free hands while stationary, so the main abilities that hominins have over quadrupedal and knuckle walking primates is that forelimbs-hands are free during locomotion walking over running. However, hands free virtually all the time probably contributed to the evolution of the hands into highly developed organs of manipulation (literally) that are better for the manufacture of tools or for affectionate stroking. Hominin Species The details of the hominin Tree of Life (“family tree”) are still being developed, but anthropologists generally agree about the primary ancestral relationships of and among hominin species. 1) The lines leading to chimpanzees, gorillas and humans are believed to have diverged sometime between 8 – 5 million years ago. 2) Fossils of the earliest hominins , from about 7 -1.8 million years ago have been found SOLEY IN AFRICA ( See discussion of Piltdown Hoax on _fake_fossils found in England). 3) Paleoanthropologists generally agree that there were more than one line of hominin species, only one of which evolved into the human or Genus Homo species. The robust australopithecines , which coexisted with early species of the Genus Homo, are not considered ancestral to humans and became extinct approximately 1 million years ago. ( https://www.britannica.com/topic/hominin ) ( https://www.youtube.com/watch?v=K3n370ww3L4 Hominin Evolution, Part 1: The First 5 Million Years ) ( https://www.amnh.org/explore/videos/exhibits/seven-million-years-human-evolution )