Transcript science
• • • • The first living organisms were simple, single celled organisms. Through time more complex simplecelled creatures were created Billions of years increasingly complex, multicellular organisms began to appear The idea that explains how this change in species has occurred over time is evolution • Charles Darwin was a person who first suggested the theory of evolution – Theory- a concept that has been tested and confirmed in many different ways and can be used by scientists to make predictions about the natural world • • • • • Born February 12, 1809 Died April 19, 1882 English naturalist Collector and geologist Proposed and provided scientific evidecne that all specias of life has evolved for time from common ancestors through the process called natural selection – Natural selectionevolution was contolled by nature rather than people • Darwin believed: – The mechanism of evolution was like the process of artificial selection practiced by breeders of plants and animals – Believed in natural selection – In natural selection individuals that survive are able to breed and pass their genetic information to the next generation – Those who are not successful in their habitat will usually die without leaving any offspring • In an environment,the individual born with a characteristic that gives it an advantage and adapts to its environment will most likely survive. • If they do survive the favorable characteristics will be passed on to many of the offspring • The characteristics that reduce an individual’s chance of surviving will decrease over time • If an individual does not have favorable characteristics it will eventually die off • • • • Over Production In each generation a species has the potential to produce more offspring than can possibly survive If too many of the offspring survive, they would overrun the Earth, although this does not happen In a stable environment the population stays the same fron one year to the next This happens because not all the individuals can survive • • • • Struggle For Survival Overproduction= competition The offspring have to cope with environmental conditions or it will die out They also need resources such as oxygen, food and shelter but they are very limited. Individuals best suited to the environment will survive and those not well suited to the environment will die off • • • • Variation The new traits that can lead to evolution come from normal variations within species. Organisms within species are never exactly alike Individuals have different variations, some better suitable to survive than others This difference is due to genetic variation – The unique combination of traits each organism inherits from its parents Selection by Environment • Traits with adaptive value in a specific environment give individuals in that environment a competitive advantage. • If the beneficial trait is past on to the offspring, they will also be more likely to survive and reproduce • The proportion of individuals with the good characteristics will increase because they are better able to compete with individuals without beneficial trait. • Later on nearly all of these individuals in the population will have the trait This change in characteristics present in population over time is evolution • There are many factors in evolution – Overpopulation= the potential for species to in crease its numbers – The limited supply of resources needed for life – The genetic variation of offspring – The selection by the environment of those offspring better able to survive and reproduce – Competition • The arrangement of an individuals DNA bases determines all the inherited characteristics of that individual • In sexual reproducing, only changes in the genes of sex cells can be passed on to the next generation and become basis for evolutionary change • Mutation and genetic shuffling is a genetic variation • Mutation is a change in the base sequence of a DNA molecule • Mutations occur at random and can’t be predicted • Mutations occur by errors of DNA as cells function but radiation and some chemicals can cause mutations • When a mutation happens they affect only that individual ; although mutations in a single celled organism or in the sex cells of a multicellular organism can be passed on the the offspring • Usually mutations are harmful and may affect the offspring so severely that it can not survive although some mutations are beneficial • Genetic Shuffling- the sorting and random recombining of genes during meiosis and fertilization results in new and different combinations of genes • The genes can be passed on to individual offspring • This process is similar to shuffling a deck of cards = the deck stays the same but the order is somewhat different • At fertilization even more variety is introduced because now cards from two decks are combined • Although mutations provide new genetic instructions, genetic shuffling is the main source of the variation that exist among the members of any sexually reproducing species • The variation of an organism within a species increase the likelihood that at least some members of the species will survive in a changed environment. • Extinction is the disappearance of an entire species • When the death rate of individuals within a species is greater than the birth rate, extinction is a possibility • Usually extinction happens when the environment changes. When an individual can not adapt to the environment changes they will die out • Fossil records show that throughout geologic time, millions of species have evolved survived for a while than died off finally becoming extinct.