Why does separation by water etc, cause evolution?

Question

Evolutionists say that a newly formed river or stretch of water can separate people, causing them, over vast periods of time, to speciate (or evolve into another species). How, then, if water was such a barrier, did humans manage to spread out over the entire planet, crossing massive seas etc?

Answer 1

The answer depends on whether you agree with the theory of evolution, or not.

Evolutionists would say that creatures evolve in order to suit local conditions. One of the problems with this theory is that too long a time-span would be required, in relation to the scientists' theory of how long the world has been habitable.

The end of your question, however, is not a good one. There are no massive barriers. The landmass of Europe-Asia-Africa is separated from America by the Bering Straits, where there might have been at one time a land-bridge. Even Australia could be reached by hopping from island to island, and New Zealand was reached by the Maoris not so many hundreds of years ago.

Answer 2

Physical barriers (such as a newly formed river or stretch of water) can be one cause of speciation.

What happens is that the geographic isolation of the two groups means that there is no gene flow between them. Over millions of years these organisms will have changed and adapted to their surroundings, and changes to their DNA will mean that even if an individual from one group meets an individual from the other (for example if a land bridge forms across the river) they will not be able to produce fertile offspring (which is what makes one species different from another)

Now where I think you may be confused is where you describe people - despite the obvious variety when it comes to appearance, humans are all one species: homo sapiens. This makes me doubt that evolutionists would use us as an example of speciation in the way you describe. The difference between humans being separated and a population of, say, cats being separated by a water barrier - is that it may prove an effective barrier for cats, but we are able to cross such a barrier using boats etc, so we would not be geographically or genetically isolated by the river. A human population would still mingle and we would not speciate.

Answer 3

Evolution theory does NOT say that separation by water, etc. "causes" evolution. Evolution just means "slow change" and this is occurring all the time. What water (and other) barriers do is to cause opportunities for that evolution to produce new species. When two populations are separated by a new barrier, to the point of genetic isolation, then the two populations will eventually lose the ability to interbreed with each other, and thus become two species. This is the most common form of species branching called "allopatric speciation."

But you are correct that water is not much of a barrier to humans once they can build boats or travel north enough to cross ice-bridges. That is precisely why humans have spread throughout the world but not speciated (branched into separate species).

But water *is* a barrier to non-tool-building primates (like pre-humans), and to other non-flying non-swimming animals. They can cross occasionally on accidental rafts or ice-floes, but that is usually a rare occurrence and causes the species to establish a new isolated population that will soon become a new species.

It is the water isolation of the Galapagos that is the precise reason it is such a fantastic place to understand evolution. You can see many examples of species that are related to species on the mainland, but are nevetheless unique species.

Answer 4

On a simle level any barrier, be it geographical or something else, can encourage the development of new species. Imagine one population is separated into two because of land upheaval. Some of the original population is trapped on one side of the upheaval and the rest is on the other side. These two populations are still the same species but, over millions of years, natural selection and mutations may change the members of each group so that they are no longer able to interbreed, i.e. they are different species. One example might be to consider that the original population lived in water. After the upheaval the pH (acidity or alkalinity) of the water in one site changed. Within the population there may be a small sub-population that are able to toerate this pH change. They become the dominant group within the population whilst the others decline in numbers. The feeding methods may change due to a change in the numbers and types of organisms living in the different areas. Again Natural Selection will favour those who are "fitter" to survive in these changing times. Natural Selection is an ongoing process and may eventually change whole populations from their normal makeup.

Answer 5

Gareth explained it well. Separation (by a river, a mountain range, an ocean, etc.) does lead to speciation, but a river is not much of a barrier to a human. A river is usually no barrier at all for a bird, but might be a huge barrier for an earthworm.
In the Galapagos Islands, you can clearly see that the ocean can be a barrier to some animals (tortoises), but not to others (sea lions).

Answer 6

Separation by water causes genetic drift over very large periods of time. Humans have spread across the globe in only the last 40,000 or so years, not enough time for different species to form. Plus, there was probably not total separation during much of that time.

A good example is camels and llamas. 65,000,000 (lots more than 40,000) years or so ago Africa and South America drifted apart. The ancestors of camels and llama could no longer interbreed as they became separated by oceans. The separation resulted in two separate species that developed and evolved over millions of years.

Answer 7

water is not a actual barrier but will cause species either side of it to behave ever so slightly different for example on one side of a river one source of food maybe plentiful where as on the other the species may have to resort to a different food source thus over years evolution will alter diet behaviour, and even look on a larger scale with oceans, for example the iguanas of the gallapogas islands are almost black in colour can tolerate high saline levels and feed on the plants growing on the sea floor, where as in other parts of the world they are green live in forrested areas and eat green vegetation, all this because of a so called water barrier. i ask is it a barrier or is it an opportunity to make a good thing better?

Answer 8

It is believed that there was a huge collision with the sun with another star and a piece came out from sun. This is known as the Earth. The Earth was thus a fireball in the beginning. However, with time the outer surface got cool down and then solidified. It was a single piece of land.Then human being was evolved in an area which was hot and humid and known as Africa nowadays. There after there was a large earth quake due to the falling of rocks under the soil, thus the huge land mass got broken in to several parts, which is known as continental drift. Nowadays we call these parts as continents. Thus the human being which was evolved in Africa got a chance to spread out to Australia, for example, which is now separated by water.
Thus, for the first time the human got separated. Now the continents got different climate and thus the human of different continents also got exposed to different climate. To exemplify, to get protection from the Sun African people developed a large amount of melanin under their skin and their skin is black in colour. Migration of human being had occur ed in recent century, which also caused generation of a mixed genetic characters.
best wishes
Biologist

Answer 9

Most of our spread has occurred during or just after the last ice age, There was no Bering straight or English channel and the Straight of Gibralter was very narrow and shallow. This allowed major migrations between places we regard as unpassable. The polynesian expansion is only 50000 years old. Almost all other human spread has occurred within written history.

Answer 10

The Continents were at one time a huge land mass that shifted apart. Read about Plate Tectonics and Continental Drift at:
http://en.wikipedia.org/wiki/Continents