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Reaction paper to planet of life apes to man

By Chris Baraniuk 30 July 2015 Evolution is one of the greatest theories in all of science. It sets out to explain life: For scientists, evolution is a fact. We know that life evolved with the same certainty that we know the Earth is roughly spherical, that gravity keeps us on it, and that wasps at a picnic are annoying.

Not that you would know that from the media in some countries, where evolution is ferociously argued about — put down as "just a theory" or dismissed as a flat-out lie.

  • For those people, it was worth carrying the sickle-cell mutation Allison discovered that the east African populations were divided into groups of lowland-dwelling people, who were prone to the disease, and people who lived in the highlands, who were not;
  • By contrast, people living in highland areas were not at risk from malaria;
  • This may seem odd;
  • The oldest fossils of all are the remains of single-celled organisms like bacteria, with more complicated things like animals and plants only appearing much later;
  • The answer is simply that evolution takes a long time to make big changes.

Why are biologists so certain about this? What is the evidence? The short answer is that there is so much it's hard to know where to start. But here is a very cursory summary of the evidence that life has, indeed, evolved. It might help to first spell out quickly what Darwin's theory of evolution actually says.

Most of us have the general idea: It is hard to accept that you are descended, through countless generations, from a worm Darwin's theory of evolution says that each new organism is subtly different from its parents, and these differences can sometimes help the offspring or impede it. As organisms compete for food and mates, those with the advantageous traits produce more offspring, while those with unhelpful traits may not produce any.

So within a given population, advantageous traits become common and unhelpful ones disappear. Given enough time, these changes mount up and lead to the appearance of new species and new types of organism, one small change at a time.

Step by step, worms became fish, fish came onto land and developed four legs, those four-legged animals grew hair and — eventually — some of them started walking around on two legs, called themselves "humans" and discovered evolution. This can be hard to believe. It's one thing to realise that you are not identical to our parents: But it is much harder to accept that you are descended, through countless generations, from a worm.

Plenty of people certainly don't accept this. But forget all the drama for a moment. Instead, begin as Charles Darwin did: View image of A domestic chicken Gallus gallus domesticus Credit: Not unexplored tropical islands or faraway jungles, but the farmyard and garden. There, you can easily see that organisms pass on characteristics to their offspring, changing the nature of that organism over time. These changes from generation to generation are called "descent with modification" Darwin was highlighting the process of cultivation and breeding.

For generations, farmers and gardeners have purposefully bred animals to be bigger or stronger, and plants to yield more crops. Breeders work just like Darwin imagined evolution worked. Suppose you want to breed chickens that lay more eggs. First you must find those hens that lay more eggs than the others.

Then you must hatch their eggs, and ensure that the resulting chicks reproduce.

These chicks should also lay more eggs. If you repeat the process with each generation, eventually you'll have hens that lay far more eggs than wild chickens do. A female jungle fowl — the closest wild relative of the domestic chicken — might lay 30 eggs in a year, whereas farm hens may well produce ten times as many.

These changes from generation to generation are called "descent with modification". Our oldest domesticated animals are still capable of rapid improvement or modification A young chick will in many ways be similar to its parents: But it won't be identical. It shows us that the tiny changes from generation to generation can add up. According to evolutionary theory, those chickens are ultimately descended from dinosaurs, and if you go further back, from fish.

The answer is simply that evolution takes a long time to make big changes. To see evidence of that, you have to look at older records. You have to look at fossils. Fossils are the remains of long-dead organisms, preserved in rock. Because rocks are laid down in layers, one on top of the other, the fossil record is generally set out in date order: I always think that the most convincing case for evolution is in the fossil record Running through the fossil record makes it clear that life has changed over time.

The oldest fossils of all are the remains of single-celled organisms like bacteria, with more complicated things like animals and plants only appearing much later. Among the animal fossils, fish appear much earlier than amphibians, birds or mammals. Our closest relatives the apes are only found in the shallowest — youngest — rocks.

By carefully studying fossils, scientists have been able to link many extinct species with ones that survive today, sometimes indicating that one descended from another.

For example, in 2014 researchers described the fossils of a 55-million year old carnivore called Dormaalocyonwhich may be a common ancestor of all today's lions, tigers and bears.

The shapes of Dormaalocyon's teeth gave it away. Still, you may not be convinced. Those animals may all have similar teeth, but lions, tigers and Dormaalocyons are still distinct species. How do we really know that one species evolved into another? View image of Microraptor was a dinosaur, but almost a bird Credit: It is also possible to observe the evolution of a new species as it happens But as we have dug up more and more remains, a wealth of " transitional fossils " has been discovered.

These reaction paper to planet of life apes to man links" are halfway houses between familiar species. For instance, earlier we said that chickens are ultimately descended from dinosaurs. In 2000 a team led by Xing Xu of the Chinese Academy of Sciences described a small dinosaur called Microraptorwhich had feathers similar to modern birds and may have been able to fly.

It is also possible to observe the evolution of a new species as it happens. This little group of birds had formed a new species In 1981, a single medium ground finch arrived on an island called Daphne Major. He was unusually large and sang a somewhat different song to the local birds. He managed to breed, and his offspring inherited his unusual traits.

  • Each of the organisms you see, whether it's a tiny insect or a great big elephant, is the latest member of an ancient family;
  • Then you must hatch their eggs, and ensure that the resulting chicks reproduce.

After a few generations, they were reproductively isolated: This little group of birds had formed a new species: This new species is only subtly different from its forebears: But it is possible to watch far more dramatic changes as they happen. Richard Lenski of Michigan State University is in charge of the world's longest-running evolution experiment.

It's a very direct demonstration of Darwin's idea of adaptation by natural selection Since 1988, Lenski has been tracking 12 populations of Escherichia coli bacteria in his lab. The bacteria are left to their own devices in storage containers, with nutrients to feed on, and Lenski's team regularly freezes small samples. They have adapted to the specific mix of chemicals he gives them.

The mixture they live in includes a chemical called citrate, which E. But 31,500 generations into the experiment, one of the 12 populations started feeding on citrate.

How do we know that evolution is really happening?

This would be like humans suddenly developing the ability to eat tree bark. All living things carry genes, in the form of DNA The citrate was always there, says Lenski, "so all of the populations have [had] the opportunity in a sense to evolve the ability to use this. But only one of the 12 populations has found their way to do this. He was able to go back through older samples, and trace the changes that led to the E. To do this, he had to look under the hood. He used reaction paper to planet of life apes to man tool that wasn't available in Darwin's day, but which has revolutionised our understanding of evolution as a whole: Genes control how an organism grows and develops, and they are passed on from reaction paper to planet of life apes to man to offspring.

When a mother chicken lays lots of eggs, and passes that trait onto her offspring, she does so through her genes. All modern life has descended from a single common ancestor Over the last century scientists have catalogued the genes from different species. It turns out that all living things store information in their DNA in the same way: What's more, organisms also share many genes.

Thousands of genes found in human DNA may also be found in the DNA of other creaturesincluding plants and even bacteria. These two facts imply that all modern life has descended from a single common ancestor, the "last universal ancestor", which lived billions of years ago. By comparing how many genes organisms share, we can figure out how they are related.

That suggests they are our closest relatives. We have a common ancestor with chimpanzees "Try to explain that in any other way than the fact that those relationships are based on a sequence of changes through time," says Chris Stringer of the Natural History Museum in London. These changes are called mutations.

This complex chain of events helps explain why only one population evolved the ability. It also illustrates an important point about evolution. A particular evolutionary step may seem extremely unlikely, but if there are enough organisms being pushed to take it, one of them probably will — and it only takes one.

But evolution doesn't always make things better. Its effects are often, to our eyes at least, rather random. The mutations that lead to changes in an organism are very rarely for the better, says Moran. In fact, most mutations have either no impact, or a negative impact, on the way an organism functions. Animals that live in dark caves often lose their eyes When bacteria are confined to isolated environments, they sometimes pick up unwelcome genetic mutations that get passed on directly to every generation.

Over time, this gradually hampers the species.