Monday January 30 y Chapter 22 Section 22 2 Adaptations are inherited characteristics of organisms that enhance their survival and reproduction in specific environments Example The finches on the Galapagos islands have adapted various beaks and behaviors in order to open the seeds on the islands Darwin explained adaptations through natural selection a process in which individu als that have certain inherited traits tend to survive and reproduce at higher rates than other individuals because of those traits Darwin wrote The Origin of Species and discussed his theory of descent with modification Darwin attributed the unity of life to the descent of all organisms from a common ancestor Darwin also believed that as the descendants of that common ancestor lived in various habitats they gradually adapted to their environments Darwin attributes the diversity of life we have today to descent with modification Artificial selection occurs in species that have been modified over generations by selecting and breeding individuals that possess desired traits Example a male peacock with large vibrant feathers is more likely to mate than a peacock with smaller feathers off of two observations Darwin argued that artificial selection occurred in nature and based his argument 1 Members of a population often vary in their inherited traits 1 Monday January 30 y Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend produce more offspring than other indi viduals 2 All species can produce more offspring than their environment can sup port and many of these offspring die and fail to reproduce This unequal ability of individuals to survive and reproduce will lead to the accu mulation of favorable traits in the population over time survival of the fittest Section 22 3 Darwin s five theories 1 Evolution has happened 2 All life has a common ancestor 3 The diversity of life is the result of a series of splits in the lineage family tree of living things 4 Natural selection is the primary mechanism driving evolutionary change Change in environment causes change in organism 5 Evolution occurs gradually over time Evidence can fall into two categories process and pattern Process is the study of evolutionary forces Why evolution happens Example Natural selection Pattern is What has happened in the history of life Five major categories of evidence for evolution 2 Fossil Record 2 Monday January 30 y Nonrandom change in form over time the fossils are not just different in the past but they are different in a consistent pattern Rocks occur in distinct layers Layers of rock that have fossils in them is the re sult of the lying down of sediments over time If you go around the world the same organisms are found in the same layers 2 Homology Comparative Morphology comparative anatomy Different species have same structures modified in different ways Notice that the same structures are repeated in very different species Example the forearm of different vertebrates human and lion are similar Homology refers to characteristics that are derived from the same structure in a common ancestor Example compound eyes are passed on from a common ancestor those structures were present in the common ancestor Function of homology may or may not be the same Function has nothing to do with homology A birds forearm may be built similar to a humans forearm but the forearm in birds is used to fly versus the forearm in humans 3 Island species Island species are similar to mainland species but unique Example the species of finches on the galapagos islands the finches on each island are quite similar but have slightly different beaks These species occur there and nowhere else this is called endemic Inferred that individuals arrived on the islands followed by evolution of new forms Oceanic islands are the result of uplift from the ocean floor and represent new land No previous contact with other land 4 Selective breeding 3 Monday January 30 y Humans choose which individuals breed and reproduce Example see which chicken lays more eggs then breed that chicken to maximize the number of eggs being laid by the offspring Much stronger than artificial breeding the offspring are not necessarily benefi cial Chapter 23 Section 23 1 Individuals within a species vary in their specific characteristics Example humans have different heights and different colored eyes These varying phenotypes reflect the idea of genetic variation where the differ ences among individuals are due to their differences in genes Usually a phenotypic characteristic is influenced by one gene with multiple alle les that produce different phenotypes Some phenotypic characteristics are influenced by more two or more genes Darwin provided evidence that life on Earth has evolved over time and he proposed that natural selection was the primary mechanism for that change Originally Darwin knew little about genetics but Mendel proposed the idea that organisms pass heritable traits to their offspring in the form of genes Sometimes genetic variation does not result because of differences in genes In this case the phenotype is a result of environmental influences 4 Monday January 30 y Example because a bodybuilder works out in the gym he has large mus cles he does not have large muscles because he inherited them through genes Therefore he will not pass on his large muscles to his offspring The only way to pass traits on to offspring and as a result create evolution ary change is through genetic variation Genetic Variation occurs as a result of three things 1 Mutation 2 Gene duplication 3 Any other process that results in new alleles new genes A mutation is a change in the nucleotide sequence of an organism s DNA In most animals the majority of mutations occur in somatic cells and are not passed on to offspring A change in a single nucleotide in a gene is called a point mutation and can sig nificantly impact the the phenotype Organism s phenotypes are matched to their environment so when a new muta tion is discovered it is usually going to be harmful to the organism Natural selection helps to remove these harmful alleles but if the allele is reces sive it is much more difficult to distinguish and remove Heterozygous protec tion occurs when a harmful allele is able to stay within a population for an ex tended period of time because it is present in heterozygous individuals where the harmful effects of the mutation is masked by the
View Full Document
Unlocking...