A molecular clock doesn't have hands. It doesn't tick. It can't give you the time of day. However, a molecular clock does tell time. Instead of telling time on a scale that involves seconds, minutes and hours, it tells time on an epochal scale that spans an entire era or longer. A molecular clock can be used to calculate the timeline for evolutionary events.
What does a molecular clock measure?
A molecular clock measures quantities of mutations or changes that have occurred in gene sequences for different species throughout a period of time. Evolutionary biologists are able to use these facts to determine how a particular species evolved. Additionally, they can use the information to obtain a date when two species split on an evolutionary timeline. A traditional clock measures time in regular intervals or ticks, whereas a molecular clock computes time from these gene changes that have a random nature.
Who created the concept of a molecular clock?
In 1962, biologist Emile Zuckerkandl and biochemist Linus Pauling presented the first concept of the molecular clock. The idea came about through observations of how genetic mutations did occur randomly but at a fairly constant rate. Thus, the theory was proposed that the number of differences that exist between any two gene sequences will increase over time. This line of thinking brought about the idea that the number of mutations that occurs in a specific stretch of DNA could be used as a time measurement.
How does a molecular clock work?
A clock must be properly aligned before it will work. A molecular clock is no exception. The first step for setting a molecular clock involves beginning with the information that is on hand for a particular species, such as fossil records. After a mutation rate has been determined, the process of calculating the divergence time for the species is fairly simple. For example, if the rate is 10 mutations every million years and there are 50 mutations within the DNA sequence, the sequences split 5 million years ago.
One interesting aspect of molecular clocks is that different genes come about at differing rates, which allows for flexibility of date events throughout evolution. In a general sense, the process of important genes evolving happens at a slower rate than that of genes that have less important functions. Thus, more quickly changing genes can be used to date evolutionary events that are more recent, while slowly evolving genes can chart ancient species splits.
What applications are there for the molecular clock?
The molecular clock is a useful application for gaining evolutionary information when there is little or no fossil record. For example, some species such as fungi, which are soft, do not make clear fossils. However, many species do leave strong fossil records and can be used to gain information about lesser-known groups.
Another useful application for the molecular clock is placing evolutionary events from a series in chronological order. This process is completed by comparing sequences from differing species to decide when they most recently shared a common ancestor, in a similar fashion to creating a family tree. This task is difficult to complete solely with fossil information, regardless of organism type.
Is the molecular clock a widely accepted scientific concept?
Although the molecular clock is considered a controversial concept, it is gaining general acceptance as we further our understanding of genome sequences. As more researchers choose to use this technique over other methods, it gains validity as a reliable timepiece.