The Cambrian Explosion: Biological Diversity Gone Wild

Babies on Land

The most conserved traits in almost every advanced organism are the stages of development. At the earliest stages of development, it is almost impossible to distinguish the embryos of mammals, amphibians, reptiles, and fish. Each starts with a tail-like protrusion and gill slits until later in development where the organisms’ shapes begin to diverge. Besides pointing towards a common ancestor, these traits also point towards the importance of a liquid environment for reproduction.

This challenge was the second large obstacle to producing organisms that could live life almost entirely independent of water. Besides seeking drinking water to maintain a stable internal environment as mentioned earlier, being able to live away from the ocean would ensure organisms can avoid predators in the sea. The brilliant solution to this problem that evolved was the innovation of the egg.

Eggs created a portable “ocean” that could be carried onto land so that embryos could develop and be born away from the ocean. This is why most, if not every, sexually reproducing land species uses some form of aqueous egg in their reproductive process. The organisms that developed these two brilliant creations are responsible for all the animals living on land today. In terms of vertebrate tetra-pods, we have indeed discovered an ancestor from which all mammals evolved (Tiktaalik).

A New Evolutionary Arena

The situation on land was much like the situation in the early diversifying oceans. After a very small number of species occupied the land, they had all the resources possible to generate incredibly diverse organisms. Once again, as predation on land began, evolution drove life to develop different traits such as fast running, quiet killing, bipedal-ism, problem solving, and many more.

Finally, as biological diversity increased in life on land, some animals found it advantageous to return to the oceans due to the intense competition they faced. This is how mammals like dolphins and whales came to reside in the oceans again.

As plants and animals continued to strive for the competitive edge, most large scale changes such as body size and visual acuity were no longer the most efficient methods of improvement. Instead, chemistry became the most useful improvement tool. I recently read an interesting story about plant and caterpillar interactions regarding this topic.