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Along path leads from the origins of primitive "life," which existed at least 3.5 billion years ago, to the profusion and diversity of life that exists today.
This path is best understood as a product of evolution.
But if a gene variant improves adaptation to the environment (for example, by allowing an organism to make better use of an available nutrient, or to escape predators more effectively—such as through stronger legs or disguising coloration), the organisms carrying that gene are more likely to survive and reproduce than those without it.
Over time, their descendants will tend to increase, changing the average characteristics of the population.
For example, in 1799 an engineer named William Smith reported that, in undisrupted layers of rock, fossils occurred in a definite sequential order, with more modern-appearing ones closer to the top.
Because bottom layers of rock logically were laid down earlier and thus are older than top layers, the sequence of fossils also could be given a chronology from oldest to youngest.
This is particularly apparent in distant remote islands, such as the Galápagos and the Hawaiian archipelago, whose great distance from the Americas and Asia means that arriving colonizers will have little or no opportunity to mate with individuals remaining on those continents.
Scientists also have gained an understanding of the processes by which new species originate.Droughts thus favor birds with strong, wide beaks that can break these tougher seeds, producing populations of birds with these traits.The Grants have estimated that if droughts occur about once every 10 years on the islands, a new species of finch might arise in only about 200 years.If a particular off- spring has traits that give it an advantage in a particular environment, that organism will be more likely to survive and pass on those traits.As differences accumulate over generations, populations of organisms diverge from their ancestors.