VIZUALIZING EARTH HISTORY By Loren E. Babcock Chapter 5 Biological Evolution

Evidence of Biological Evolution and Natural Selection Explain the meaning of biological evolution. Evolution - Change through time (usually applied to biological organisms). Changes that occur within a species or population from one generation to the next, as parents pass their morphologic, behavioral, and other traits on to their offspring, represent microevolution.

Evidence of Biological Evolution and Natural Selection Darwinian synthesis By the mid 1800s, biological evolution had become widely accepted as a scientific theory. Although it was (and still is) accepted by practicing scientists with the highest degree of certainty, opinion differed on its driving force. The mechanism that drives biological evolution —natural selection— was first put forward in separate publications by Charles Darwin and Alfred Russell Wallace (1859).

Evidence of Biological Evolution and Natural Selection Explain natural selection and how it operates. Natural selection - The process by which individuals best suited to their environment survive and reproduce, and less well suited individuals are eliminated from the population. To provide supporting evidence for the concept of natural selection, Darwin addressed embryology, homologous structures, vestigial structures, breeding experiments, the fossil record, and adaptation.

Evidence of Biological Evolution and Natural Selection Explain natural selection and how it operates. Homologous structures - Morphological features in biological organisms that have a similar position and evolutionary origin, but not necessarily identical structure or the same function. Analogous structures - in organisms have essentially the same function, but different evolutionary origins. Birds, bats, and insects have all evolved wings for flight, but they have done so by different evolutionary means.

Evidence of Biological Evolution and Natural Selection Explain natural selection and how it operates.

Evidence of Biological Evolution and Natural Selection Explain natural selection and how it operates. Vestigial structure - Structure in an organism, usually reduced in size or function compared to the homologue in earlier species of the evolutionary lineage; it is in the process of disappearing. Selective breeding – is a process in which humans decide which desirable traits should be concentrated in breeding, is exemplified in the many breeds of dogs, all of which have a single ancestor, the gray wolf.

Evidence of Biological Evolution and Natural Selection Explain natural selection and how it operates. Adaptation - The process of modification of an organism or its parts making it more fit for survival in an ecological niche. The word can also refer to a trait that helps an organism survive in its ecological niche. Darwin and Wallace separately proposed natural selection as the mechanism to explain how descent with modification (or evolution) happened. Natural selection is based on the observation that populations (or species) are usually composed of more individuals than the environment can support.

Variation and Inheritance of Traits Explain the origin of variation in populations and explain how changes can be inherited. Gregor Johann Mendel carried out experiments on garden peas in the 1850s and 1860s, demonstrated distinct, replicable patterns underlying inheritance, and developed a conceptual model for heritability that explained the patterns. The work laid the foundation for modern genetics, which is the branch of biology concerned with heredity and variation.

Punnett Square

Variation and Inheritance of Traits Understand the structure of genetic material. Genetics - The branch of biology concerned with heredity and variation. Genetic changes underlie the morphological changes recorded in the fossil record. Genetic variation and inheritance of adaptive traits make natural selection possible. Genetic changes in modern organisms can be used to track evolutionary history, and even to provide some sense of the timing of evolutionary events.

Variation and Inheritance of Traits Understand the structure of genetic material.

Variation and Inheritance of Traits Modern genetics: genes, chromosomes, DNA Gene - Unit of chromosomal information about a heritable trait that is passed on from parents to offspring. Chromosome - Genetic structure by which hereditary information is physically transmitted from one generation to the next. The DNA molecule usually consists of two spiral strands, known as a double helix. It contains genes, which are the hereditary units that Mendel thought of as unit factors.

Variation and Inheritance of Traits Modern genetics: genes, chromosomes, DNA Cells store genetic information in DNA (deoxyribonucleic acid) molecules. In eukaryotes, the DNA resides in the cell nucleus, but prokaryotes lack a nucleus to contain the DNA.

Variation and Inheritance of Traits Modern genetics: genes, chromosomes, DNA Meiosis - Division of chromosomes to produce two haploid cells as gametes necessary for sexual reproduction are produced. Mitosis - Division of cell nuclei in which the parental chromosomal number is maintained; it is the basis for bodily growth and asexual reproduction.

Variation and Inheritance of Traits Mutations, adaptations, and random factors Mutation - Heritable change in DNA or chromosomal structure that results in new versions of genes, and ultimately, of life’s diversity. Molecular clock - The concept that genetic mutations occur at a known rate, and if the rate is known, the number of genetic differences between separate species can be used to measure the amount of time that has elapsed since the species diverged.

Variation and Inheritance of Traits Mutations, adaptations, and random factors

Speciation processes Speciation - The evolution of a new species from an ancestral species. Speciation, or the rise of a new species from an ancestral species, in sexually reproducing organisms, can occur according to one of three general models. Allopatric Speciation Sympatric Speciation Parapatric Speciation

Speciation: Processes and Rates Allopatric speciation, emphasizes disruption of gene flow between populations, usually by some sort of physical barrier. Sympatric speciation, involves the rise of a daughter species from a group of individuals within the geographic range of an ancestral species. Parapatric speciation, a daughter species might arise through hybridization of two populations.

Speciation: Processes and Rates SpePECIATION PROCESSES The fossil record shows two different speciation patterns, cladogenesis and anagenesis. Cladogenesis is a branching speciation pattern, and it applies to populations that become reproductively isolated and then diverge genetically from each other. Anagenesis refers to changes in allele frequencies that occur along a single evolutionary pathway. The parent species and daughter species are connected by intermediates.

Speciation: Processes and Rates SPECIATION RATES Charles Darwin’s claimed that evolution occurred slowly, the result of a gradual accumulation of changes from one generation to the next and through phylogeny, or an evolutionary series. Phylogeny - The line or lines of descent in an evolutionary series. Phyletic gradualism - Speciation rate characterized by a slow, gradual pace.

Speciation: Processes and Rates SPECIATION RATES Niles Eldredge and Stephen Jay Gould proposed punctuated equilibrium as a theory of evolutionary biology. Punctuated equilibrium - sexually reproducing populations experience little change for most of their geological history, and that when phenotypic evolution does occur, it is localized in rare, rapid events of branching speciation (called cladogenesis). Phyletic gradualism – Contrasts with punctuated equilibrium, because it states that evolution generally occurs uniformly and by the steady and gradual transformation of whole lineages (anagenesis).

Speciation: Processes and Rates SPECIATION RATES

Phylogenetics: Reconstructing Evolutionary History Understand how an evolutionary hypothesis is represented on a cladogram. A group of species that includes the ancestor and all of its descendants is called a clade (monophyletic group or natural group). The classification of species will follow along the lines of clades, but in practice this is not always the case. Instead, so-called artificial taxa are used in many circumstances. There are two basic types of artificial taxa: 1, paraphyletic groups, in which one or more groups descended from the common ancestor are excluded from the group; and 2, polyphyletic groups, in which members of the group have separate ancestors.

Evolutionary Patterns and Trends Study of evolutionary history shows that certain patterns or trends have occurred in group after group over a period of millions of years. IRREVERSIBILITY OF EVOLUTION Early in the 20th century, the Belgian paleontologist Louis Dollo observed that evolution cannot produce exactly the same species more than once. This concept of the irreversibility of evolution has come to be known as Dollo’s Law.

Evolutionary Patterns and Trends CONVERGENT EVOLUTION Convergent evolution is the evolution of similar body forms in two or more biological groups. Similar body forms apparently evolved in different taxa that used similar ecological strategies, or as a response to similar ecological pressures. Adaptive radiation - Rapid evolution of organisms to fill new ecological niches. Adaptive radiation occurs when life forms rapidly diverge to fill a variety of niche spaces that have become open to them.

Speciation: Processes and Rates SPECIATION RATES

Speciation: Processes and Rates SPECIATION RATES Charles Darwin’s claimed that evolution occurred slowly, the result of a gradual accumulation of changes from one generation to the next and through phylogeny, or an evolutionary series. Phylogeny - The line or lines of descent in an evolutionary series. Phyletic gradualism - Speciation rate characterized by a slow, gradual pace.

Evolutionary Patterns and Trends Adaptive radiations – Increase in body size In the late 1800s, the American paleontologist Edward Drinker Cope observed a common tendency for animals to increase in body size through an evolutionary lineage. This trend is often called Cope’s Rule. Horses, for example, were represented in the Eocene by a small animal known as Hyracotherium. Subsequent horses tended toward larger size. The living species, Equus caballus, is about four times the size of Hyracotherium.

Evolutionary Patterns and Trends Adaptive radiations - Heterochrony Heterochrony involves evolutionary changes in a lineage that result from changes in developmental timing. There are two forms of heterochrony: Paedomorphosis, adults of the descendant species look much like juveniles of the ancestor. Peramorphosis, the onset of sexual maturity in the descendant is delayed in comparison to the ancestor. The descendant continues to show development of characters that the ancestor did not show.

Evolutionary Patterns and Trends Adaptive radiations - Asymmetry Natural selection has had a long history of reinforcing right-left behavioral differences in species. Ambidextry, or equal capability of the right and left sides, has tended to be selected against. It seems more adaptive for individuals to have a preferred lead side if they are to perform well in most functions, especially running or swimming from predators.

Extinction Extinction is the annihilation of all individuals of a species. Every species that evolves eventually becomes extinct, so extinction can be view as a natural part of the evolutionary process. A certain percentage of the world’s species can be expected to become extinct during any interval of geologic time, and the normal flux of extinction can be thought of as the background level of extinction. Mass extinction - When numerous species become extinct within a geologically short time interval.