Latin enthusiasts know that circadian means circa (about) and diem (day). So, a circadian clock is a biological rhythm whose oscillation from a starting condition and return to that condition, occupies about twenty-four hours. The cycle is not precise however. It may run a little fast or a little slow. Studies with flowers that close at night, for example, reveal that when the plant is put into complete darkness for a number of days, the plant will continue to show these oscillations, more or less according to a 24 hour clock, but not exactly. Our cat, for example has a wonderful biological clock! However, that clock runs a little fast each day, so that the cat is always demanding food a little too soon!
In the 1960s biologists came to suspect that biological clocks were almost universal. They studied the cycles of such organisms as bioluminescent algae, and the results proved inspirational. It became apparent that the activities of these organisms must be controlled by an internal clock mechanism instead of their just observing the dawn each day. In the mid-1970s, biologists believed that all eukaryotic organisms exhibit internal time keeping, but not blue-green algae (cyanobacteria) which lack a defined nucleus. Finally in 1998 a report was published that cyanobacteria also exhibit a biological clock. However, the proteins involved in the cyanobacterial clock are completely different from those in other organisms. This demonstrated that a single evolutionary origin of clocks was not what we observe. This seems like another complicated feature of organisms which displays multiple origins (or separate designs). This is not an evolution friendly conclusion.
By the year 2000, some proteins related to timekeeping had been uncovered in organisms like bread mold, but nothing like in a mammal. Then such a protein was identified in mice. Subsequently biologists began to develop models that involved a number of interacting proteins. Biologists had hoped to use an easy-to-culture model organism to study biological clocks. They had hoped that the fruit fly could represent their general model, but they soon discovered that in its clock keeping proteins, it is different from a number of other insects and thus it was not necessarily typical. The fruit fly exhibits only cryptochrome 1 (hidden pigment responsive to blue light) while honey bee and red flour beetle exhibit only cryptochrome 2. Then there is the Monarch butterfly which exhibits both these cryptochromes in a pattern of relationships that is similar to mammals.
Basically, at night various proteins are synthesized, increasing to maximum levels sometime after dawn. During the day time the proteins break down and fall to minimum levels sometime after dusk. Some proteins modulate the activities of others in an elaborate dance. At dawn, Cryptochrome 1 initiates the breakdown of the protein Timeless. But Period interacts with Timeless to keep it from degrading too rapidly, and Period also protects Cryptochrome 2 from declines until late in the day. Period also assists Cryptochrome 2 to enter the nucleus and keep the proteins Clock and Cycle from promoting the synthesis of all these proteins during the day. At night once most of these proteins have basically disappeared, the duo of Clock-Cycle connects to the appropriate genes in the DNA, promoting the renewed synthesis of all these proteins. The event that keeps the cycle locked into the day/night cycle is the response of Cryptochrome 1 to light at day break.
Biologists have studied the Monarch butterfly’s circadian rhythms because they are closely connected with the ability of these insects to migrate thousands of kilometres to destinations which only their distant ancestors have previously visited. Not only do the butterflies have a circadian rhythm which compels them to migrate only at the correct times of the year, but this internal clock also enables the butterfly (assisted by an internal compass) to track the sun across the sky and to adjust its direction relative to the sun’s position in the sky. Therefore, the butterfly pursues a steady south west course in the fall, and a steady north east course in the spring. That these abilities are programmed into these insects is nothing short of astonishing! If nothing else shouts “design” to the secular scientist, this situation certainly should do so!
The unexpected situation of different organic molecules underlying the circadian clocks in various organisms, is explained by evolutionists as resulting from convergence, not descent with modification from a common ancestor. Of course, God the Creator, obviously chose which creatures to provide with any given molecules. There are few more compelling indicators of design than the circadian rhythms and navigational skills of insects.