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Natural Selection is not actually different from Evolution. It is part of the Theory of Evolution. Actually, it is the most vital part of Darwin's 'Evolution of Species' - How evolution happens. We may know that Evolution of a species happens over time, but how it happens is what Natural Selection explains. There is sufficient evidence in the Fossil Record to prove that Evolution is a fact. (But it is not a Law).
And it proceeds slowly over time - in the millions rather than hundreds or even thousands of years. (But there are exceptions which are explained below eg. if two islands become separated). If Evolution is a fact, then explaining how it happened is part of it.
Natural Selection is the process which drives Evolution.
The basic idea of Natural Selection is that Nature 'calls the shots'. This means that rather than just having 'ideal' offspring being created accidentally by mutations, the survival of a new generation of any species (the 'fittest'), is a direct result of how they respond to constantly changing environmental conditions which may happen slowly as in the beginning of an Ice Age, or suddenly as in a cataclysmic event such as the Asteroid which hit the earth 65 million years ago.
The Dinosaurs had ruled the earth for hundreds of millions of years - a staggering amount of time - but when the Asteroid hit, it wiped out not only most of them, but most of all living species. However, there were enough species which were specifically adapted - those who already had - as the result of mutations - the right genes to cope with the huge environmental changes which occurred.
One result of this event was that the whole earth caught on fire ('Fireball Earth') and only creatures who lived underground or in other tiny niches somehow protected from the fire, and whatever else came raining down, survived. That explanation is, however, only a theory, but probably the most likely one.
"On one clear day 65 million years ago, the sky suddenly fell in, and 80% of all life became extinct. But this cataclysm also opened the door for humans to inherit the Earth". Cosmos Magazine.
This included plants, of course. And the grasses were one species which made use of their ability to recover from underground - just below the surface - as they still do today after bushfires which kill all the trees. It has recently been discovered that fire resistance is the reason that grasses are the dominant vegetation on the African savannas. This fact alone is argued to be one of the reasons why early hominids were able to evolve more quickly than if they had stayed in the trees. And more and more plains were being created, and still are, because the Great Rift Valley is pulling Eastern Africa apart.
And if you think the Asteroid catastrophe 65 mya was bad, you may be interested to know that 250 mya there was something far worse: The Great Dying.
Then we have this week's close and closer encounters. As they say, 'It's not a matter of IF, but WHEN'. Feb 15, 2013. Meteor hits Earth with a bang.
If there is a sudden change in the environment only a species well adapted will survive.
As far as reproduction goes, males compete to mate with a female, but Darwin placed this as secondary to ecology. Nature does not separate sexual selection from ecological selection. If a certain beneficial characteristic increases the rate of survival in a species then those individuals who do not possess it will not survive, thereby gradually ensuring the survival of that particular species with that particular benefit. Successful progeny replace the unsuccessful, ridding a population of that less beneficial trait.
Humans are the most adaptable creatures on the planet, with their brain being highly developed, giving them the ability of 'thinking themselves' around many environmental problems which may be thrown at them. And Mankind actually almost reached the point of extinction about 73,000 years ago when the Mt. Toba volcano erupted on the Island of Sumatra in Indonesia. This was no ordinary volcano. It was, and still is, a Super Volcano (like the one in Yellowstone National Park in the USA).
To put it briefly, it wiped out just about everything in the line of fire which did not have a hiding place or protection of some kind. In fact, the only Humans who survived were the ones who were not directly affected by the ash and deadly sulphurous cloud (which spread many miles up and across the oceans to Europe and parts of Asia) and who could 'adapt' afterwards to the radically changed environment and food sources.
We were lucky, as we have been many times in the past and no doubt will be many times in the future. This information comes from Brian Fagan's book 'Cro-Magnon. 'How the Ice Age gave Birth to the first Modern Humans', which is a fascinating account of Mankind after we came out of Africa, all those thousands of years ago. Only as few as 10,000 humans or maybe less survived Mt. Toba. Staggering.
If you would like the easy version of how Natural Selection works, just try this site. It has a wonderful history of earth timeline:
Over time, successful traits remain because they give the individuals more chances to reproduce and leave more offspring. Characteristics become more specialized as this process continues.
For a species to survive, it must overcome the forces of Nature - predators, stress, and the environment itself. It must also live to pass on the positive genes which make it 'survivable'.
If one species becomes separated from another, eventually they will become so different that they can no longer interbreed. The Galapogas Islands are living testimony of this. Different species are evolving on different islands relatively fast compared to 'normal' evolution. If this happens, they can become considered different species altogether eg. when Gondwanaland broke up, different species sprang up depending on which 'bit' they were living on at the time. And they had plenty of time considering that the continents were and still are moving apart at about the rate our fingernails grow. A long time.
Of course, the continents are doing other things as well (eg. sliding past each other - the San Andreas Fault), diving beneath each other (eg. Japan), etc. In fact, Australia is heading for India (again) and has already been two and a half times round the globe. Part of Australia is already lying underneath Tibet, and there are even sea shells on top of the Himalayas! But that's another topic - Continental Drift.
A good example of this is the theory that some sea turtles travel thousands of miles to lay their eggs. Why? Because their normal route dating from ancient times, lies on two different continental plates which are drifting apart. When these turtle first evolved, the route they took was much shorter. I read this in an old copy of New Scientist years ago.
This is why a species will sometimes separate into multiple species, rather than simply being replaced by a newer form of the species (from this fact Darwin suggested that all species today have evolved from a common ancestor').
The following site is a lot of fun and tells you all you need to know about Darwin and Natural Selection. The human brain is evolving all the time and one day, who knows, we might just look like this:
Perhaps the most radical claim of Darwin's theory of evolution through natural selection is that "elaborately constructed forms, so different from each other, and dependent on each other in so complex a manner" have evolved out of the simplest forms of life and according to a few simple principles.
This theory has a lot of support but also a lot of opposition - always a healthy thing in science (as it is in politics).
Natural Selection. Fact or Theory?
It is called a theory out of convention. Some biologists refer to it as Darwin's Law of Evolution, because it is pretty well established.
In science, a theory is any well substantiated explanation for some aspect of the world. That is why we have Newton's theory of gravity, and Einstein's even better theory of gravity (General Relativity).
Evolution is both a well established fact (it has been observed, and it explains the sequence and arrangement of the fossil record), as well as a scientific theory (descent with modification) or random mutations coupled with natural selection, or that most modern (and extinct) species share common ancestry.
Evolution is a fact, not a theory. This means that we have enough evidence to support the fact. How its proceeds are the various theories.
When people use the term 'theory of evolution' they are generally referring to Darwin's theory of how evolution progresses. Which is through natural selection. That is a theory not a fact.
To sum up, Natural Selection is the process which drives Evolution.
Fossils of prehistoric plants.
Eocene fossil flower, Clare Family Florissant Fossil Quarry, Florissant, Colorado, USA. Such a window into the past. A real flower.
Crossotheca hughesian Kidston, an ancient pollen organ in the Sedgwick Museum, Cambridge, UK.
Fossil of Archaefructus Flowering Plant. Beautiful.
Ginkgo biloba Eocene fossil leaf from the Tranquille Shale of MacAbee, British Columbia, Canada.
Glossopteris browniana. A Fossil from the Permian Era.
These are the largest group of fossil plants found so far. They grew in the areas on the following map of the world as it was way back then. More than 70 fossil species of this genus have been found. The Permian Era began about 299 million years ago and lasted until around 253 million years ago. That's about 46 million years during which these ancient plants lived on Earth.
Map of the world after Gondwana started breaking up. It shows where the Golossopteris ferns lived.
Arcaeamphorus longicervia. Artist's impression. The first carnivorous plant.
Trochodendron nastae. Angiosperm fossil.
Fossil flower in copal. Madagascar.