How Does Evolution Work

how does evolution really work the primary way that evolution occurs is through the action of natural selection that is populations change in response to environmental pressures and they become adapted to new conditions and they change over time following Charles Darwin's lead biologist Krish Nider and his colleagues traveled to Ecuador to study the evolution of several animal species this lush rainforest is a natural laboratory for ongoing investigation of evolutionary theory natural selection is at the core of their research on hummingbirds in our research we're trying to understand how new species arise this is Darwin's fundamental question on the Origin of Species how do new species arise and what we're finding is that natural selection seems to be an incredibly important factor in generating new species natural selection the key evolutionary mechanism and Darwin identified is really four processes genetic variation over production of offspring struggle for existence and differential survival and reproduction first genetic variation individuals within a species vary from one to the other for evolution to work by natural selection the characteristics that give an individual an advantage in a certain environment have to be passed on from one generation to the next and in hummingbirds bill length seems to seems to have a very strong genetic basis that is if two parents mate and both of those parents have long bills their offspring will have long bills if those parents have shorter bills their offspring will have shorter bills second there is overproduction of offspring Darwin realized that natural selection would operate because individuals in natural populations tend to produce more offspring than can survive for example hummingbirds over their lifetime will often produce dozens of offspring but only one or two of those individuals are likely to survive the third factor in natural selection is the struggle for existence and that leads to differential survival and reproduction in any population whether it's plants or animals or whatever this excess production of individuals results in this and what Darwin called the struggle for existence and what he had in mind there I think was the competition for food and space and mates as well hummingbirds compete for nectar they often compete very fiercely for limited resources natural selection will favor individuals that that are more efficient at getting nectar and natural selection will result in changes in wing shape that allow hummingbirds to fly longer distances for instance or maybe to be more maneuverable to maneuver around flowers and get nectar more efficiently and probably most importantly it'll affect the length and shape of the bill bill measurements in the case of hummingbirds we know that a 1 or 2 millimeter change in length can have profound differences on how efficiently that bird feeds and how well it survives individual survivors are more likely to reproduce and pass on their advantageous as well as other genes to their offspring in an environment with long flowers having a long bill is an advantageous trait not necessarily the absolute best trait always just a better one in this environment hummingbirds with small bills may not survive and eventually there will only be hummingbirds with long bills over a long period of time the entire population of hummingbirds adapts to the shape and size of the flowers that exist in that environment if you're in the woods and you're walking with another person and you come on a bear and the bear chases you you don't have to be faster than the bear you only have to be faster than the other person because the bear eats them and you get away species cannot develop the adaptations that benefit them in their lifetimes just as you cannot make your arm longer to reach a book on the shelf up high individual small build hummingbirds that move into an area where there are longer flowers can't make their bills longer their bill length is determined by the DNA they inherited from their parents Schneider uses hummingbird DNA sequences to reconstruct their evolutionary history as it has been shaped by natural selection genetic variation over production of offspring struggle for existence and differential survival and reproduction we're just essentially doing what Darwin did but with a with a bunch of fancy new tools we're using molecular biology we're using modern computational methods and all these things but we're just doing basic Natural History really and in the hummingbirds we found that that many of the species are relatively young that is they evolved in the last 2 or 3 million years which is pretty quick on an evolutionary timescale Darwin emphasized over and over I mean repeatedly in the Origin of Species the fact that small changes would accrue every generation and that over the enormous length of time that life has been present on earth these changes could build up to amount to enormous changes it was Charles Darwin's genius to have identified natural selection as the central force in evolution and I think that in research over the last 10 or 15 years has really supported that I think most evolutionary biologists would agree that natural selection is probably the single most important force in evolution