Natural selection Anthro How did a world filled with only single celled organisms become filled with all of the organisms we see today Natural selection Organisms are best able to survive and reproduce in their environment well become more numerous while those who are less able will decrease in number Weaning out those individuals who cant survive as well as their competitors When a population of organisms survive Which individuals are most likely to survive a Survive into old age b Produce lots of off spring 3 necessary and sufficient conditions for evolution by natural selection 1 There is variation among individuals 2 The variation is inherited by off spring so trait goes down in lineage 3 Different variants have differing probability of survival and reproduction Essential for reproduction Natural selection nonrandom differential reproduction of individuals based on heritable traits Evolution changes in gene frequencies within population What is the difference Evolution is the overall process natural selection is a mechanism Our vision is an example of natural selection Evolution is the overall process natural selection is a mechanism There is major variation among individuals eye skin color weight height metabolism etc Wanting to have many offspring Humans display large variation in the number of the offspring they produce Partly due to environment Partly due to genetics Natural selection Depending on your environment slight mutations that occur within an individual that are beneficial to their survival or reproductive habits What is the unit of selection for natural selection Individual gene Natural selection acts on individuals When will natural selection have the largest effect When there are only enough resources for SOME individuals to survive and reproduce Natural election is a competitive process Populations reach a carrying capacity beyond which not all individuals can survive and reproduce Important points The original source of by variation in populations is mutation A random event These random mutations can lead to differential reproductive success Natural selection is a passive process We are naturally selected rather than dogs or other animals which we artificially mate due to the ones with more beneficial traits Natural selection is a passive process traits being passed on are one that make you choose better mates Specifically choosing to improve the species not random if you do not have a beneficial mutation then you are most likely going to die off Adaptations are traits that increase the likelihood that an organism survives and reproduces Traits favored by natural selection are adaptations What is not an example of a human adaptation The size and shape of the female birth canal Natural selection has no goal it s a passive process