Google is considered the largest and best search engine today, and is therefore considered as a reference. All other search engines are always running behind the news from Google, it also being the main (and sometimes sole) focus of the professional
SEO. And they are not wrong. Google grasps currently about 70% of the market for search engines in the world and this percentage is even higher! Reaching 80%.
Moreover, India and Brazil are the countries where the Orkut and Gmail has the highest percentage of users in their respective markets (Social Networks and e-mail), by these and other reasons,
Website Optimization in the world is almost entirely focused on Google. But what about the other 20-30% of searches carried out? You can not throw away does not it! Many people do not know, but there is one interesting fact about the
major search engines of the world: they are related!
Relationship Between Search Engines
Some professionals in the field of Web Marketing, Search Engine Optimization or Web site design, have already noticed this fact: performing a search in different search engines often have similar results and in extreme cases to equal results. But why this happens? It's because they are related. Many search engines smaller (and less profitable) and even some free (search engines are purely non-profit programs such as Adsense), it has the technical and physical (hardware) to develop their own systems of crawlers (like the Googlebot) And then enjoy the results of other large systems such as Google and Yahoo.
Incidentally today among the leading search engine market, Google and Yahoo may be considered the major influences. Yahoo is the case, had reduced its importance, especially from 2000 onwards, but it used to be the
biggest search engine in the world at the time of the beginning of Google and still has its strength in European and American markets, these markets the Yahoo has a greater focus on Search Engine Optimization.
An interesting fact that, the enormous influence that the directory
Dmoz has on the Internet. It is regarded as the basis of virtually all search engines, the

Google. The Dmoz occupies that position primarily because of its historical importance (one of the first directories of success in the world), due to their seriousness and mainly due to the fact that human-powered, ie, all sites submitted to Dmoz are examined by the same people, being approved or disapproved according to the sense of them and also according to technical criteria.