Bitcoin dominance (BTC) has changed a lot over the years, albeit always slowly.
First of all, you need to understand exactly what is meant by Bitcoin dominance. It is the percentage of market capitalisation held by Bitcoin in relation to the total of all cryptocurrencies. Therefore it is a percentage that theoretically can only vary from 0% to 100%.
Obviously, when only Bitcoin existed, this percentage was 100%, whereas now, according to CoinMarketCap data, it has dropped to around 60%.
Always taking as reference the CoinMarketCap data, which is missing the data prior to April 2013, just on this date the bitcoin dominance had already dropped to 94%.
Bitcoin vs Litecoin for dominance
In fact, it must be remembered that the first altcoins, like Litecoin, were even born in 2011, so in fact only in 2010 was the dominance of bitcoin 100%.
As for 2009 instead we do not have BTC exchange rates on the exchanges, because at that time there were no exchange crypto, so the market capitalization of bitcoin can be calculated only from 2010.
Until December 2013 bitcoin dominance remained above 90%, falling to 87% in March 2014.
It fell below 80% only in December of the same year, when the price of BTC fell to $300 after the first big speculative bubble burst at the end of 2013 which had brought it up to over $1,100.
Bitcoin and the rise in dominance of Ripple
In fact, in 2013 Ripple (XRP) was born, which in December 2014 reached a considerable dominance of over 13%.
The maximum dominance of XRP was then reached in May 2017, with over 17%, while due to the large speculative bubble at the end of 2017 it peaked at over 15% in January 2018.
In 2015 Ethereum was born, but it did not reach a significant dominance until March of the following year, when it exceeded 13%.
During the same period, bitcoin dominance fell to 76% for the first time in history, but soon recovered to 87% at the beginning of 2017.
In 2017, bitcoin dominance collapsed due to the speculative bubble that caused the value of ETH, XRP and other cryptocurrency to skyrocket.
The lowest peak ever reached by bitcoin dominance was on 15 January 2018, when it fell below 33%.
It has to be said, however, that although it was well below 50%, no other cryptocurrency could do better at that time either, with ETH at 19%, XRP at 10%, and the remaining cryptocurrencies splitting the remaining 38%.
However, mainly due to the decline in the value of the altcoins, a long and slow rise in bitcoin dominance began as early as February 2018, with a new peak in September of the following year, reaching almost 70%.
Since then it has slowly decreased to the current 60%.
Altcoin and Bitcoin prices
The dominance of bitcoin tends to vary little over the short term, and when it varies it often does not do so with large, fast excursions.
This is because very often the prices of altcoin are influenced by those of bitcoin, therefore often their market capitalization moves proportionally.
Moreover, in relatively calm period, when the dominance of BTC goes down it tends then to go up again, always because the prices of the altcoin tend to follow those of bitcoin.
The more meaningful variations there are when they are formed of the true and own bubbles for example on the price of some altcoin, that however tend to burst in order to bring back on the medium/long term the things more or less always around a level of equilibrium.
Before 2017 this level of equilibrium was around 80% dominance per bitcoin, while afterwards it was between 50% and 70%.