Chapter 4 Evolution Genetics and Human Variation Humans have uniquely varied ways of adapting to environmental stresses evolving human populations adapt genetically in response to environmental forces and individuals react physiologically to stresses I The Origin of Species according to creationism biological similarities and differences originated at the Creation genesis Carolus Linnaeus developed the first comprehensive classification of plants animals fossils showed that different kinds of life once had existed therefore creationism could not be real bc if all life had originated at the same time why weren t ancient species still around creationism plus catastrophism arose to replace original doctrine in this view natural disasters destroyed all ancient species including biblical flood nd after each event God had created again leading to contemporary species Theory and Fact evolution transformism alternative to creationism and catastrophism evolutionist believe that species arise from others through a long and gradual process of transformation or descent with modification Charles Darwin uniformitarianism present is the key to the past explanations for past evetns should be sought in the long term action of ordinary forces necessary building block for evolutionary theory doubt that world was only 6 000 years old takes much longer for major geological changes so applied this idea to living things this longer time span allowed enough time for the biological changes that fossil discoveries were revealing Darwin said natural selection was powerful evolutionary mechanism that could explain the origin of species biological diversity and similarities related life forms theory set of ideas formulated by reasoning from known facts to explain things main value of a theory is to promote new understanding a theory suggests patterns connections and relationships that may be confirmed by new research the fact of evolution that it has occurred was known earlier the theory of evolution through natural selection how it occurred Darwin s contribution natural selection process by which the forms most fit to survive and reproduce in a given environment do so in greater numbers than others in the population a natural process that leads to a result operates when there is competition for strategic resources necessary for life such as food and space between members of the among was same population for natural selection to work on a particular population there must be variety within that population as there always is evolution works as the process of natural selection takes advantage of the variety that already is present in a population doesn t variation genetic inheritance industrial melanism industrialization in UK led to darker peppered moths being the more favorable evolutionary theory is used to explain rely on associations and theories an association is an observed relationship between two or more variables a theory is more general suggesting or implying associations and trying to explain them the truth of a scientific statement is confirmed by repeated observations create II Genetics for natural selection to operate must be variety in the population undergoing selection human biological diversity variety genetics helps us understand the causes of biological variation biochemical changes mutations in DNA provide much of the variety on which natural medelian genetics studies the ways in which chromosomes transmit genes across the selection operates generations biochemical genetics examines structure function and changes in DNA population genetics investigates natural selection and other causes of genetic variation stability and change in breeding populations Mendel s Experiments studied inheritance of pea plants discovered that heredity is determined by discrete particles or units concluded that although a dominant form could mask the other form in hybrid individuals the recessive trait was not destroyed these basic genetic units are what we know as genes or alleles which are located on chromosomes 46 arranged in 23 pairs one from father one from mother gene determines wholly or partially a particular biological trait alleles biochemically different forms of a given gene heterozygous mixed alleles homozygous possessing two identical alleles of that gene genotype hereditary makeup what you are genetically phenotype expressed physical characteristics what you appear as Independent Assortment traits are inherited separately from one another independent asst and recombination of genetic traits provide one of the main ways by which variety is produced in any population organism develops from a fertilized egg zygote created by two sex cells zygote grows rapidly thorugh mitosis cell division sex cells are produced by meiosis four cells produced from one III Population Genetics studies stable and chaging populations in which most breeding normally takes place gene pool refers to all the alleles genes chromosome and genotypes within a breeding population genetic evolution change in gene frequency frequency of alleles in a breeding population from generation to generation mechanisms of genetic evolution natural selection mutation random genetic drift gene flow any factor that contributes to change in allele IV Mechanisms of Genetic Evolution 1 Natural Selection stresses from can operate only on phenotype harmful recessive gene cant be eliminated from the gene pool f it is masked by a favored dominant phenotype includes not only outward physical appearance but also internal organs tissues and cells and physiological processes and systems many biological reactions are not automatic genetically programmed responses but the product of years of exposure to particular environmental human biology has considerable plasticity is changeable due to stresses environment works on the genotype to build the phenotype and some phenotypes do better in certain environments that others do directional selection traits that have proved to be the most adaptive favored by natural selection in that environment will be selected again and again generation to generation given this directional selection long term selection of the same traits maladaptive recessive alleles will be removed from the gene pool will continue as long as env forces stay the same but if the env changes new selective forces start working sexual selection based on differential success in mating process in which certain traits of one sex are selelcted bc of