• Question: What is the cause of the apparent rapid diversification of multicellular animal life around the beginning of the Cambrian, resulting in the emergence of almost all modern animal phyla?

    Asked by Honey_Badger_03 to Cristiane, Nicki, Nikolai, Richard, Samuel on 9 Mar 2015.
    • Photo: Nicki Whitehouse

      Nicki Whitehouse answered on 9 Mar 2015:

      This isn’t really my period or area of expertise but the Cambrian explosion was proceeded by a period of major extinction. Periods of extinction are often succeeded by periods of species expansion and diversification and in that respect the Cambrian is not unique. There have been other periods where extinction is followed by major diversification. As a biologist I would say that when you have a major extinction event you have many niches suddenly becoming available; new taxa come in to take over these previously occupied niches. This is also a period of major environmental change when species are adapting to new conditions. Finally, I think the fossil record gives the appearance of something occurring more rapidly than may actually have been the case, making it look like a rapid speciation event when the reality may have been much slower. I’m happy to be corrected on all of this, however, my period of interest is the Quaternary, the last 2.5 million years.

    • Photo: Samuel Ellis

      Samuel Ellis answered on 9 Mar 2015:

      For a start it all depends on your definition of rapid, seeing as this was a period of many millions of years! Also when you look that far back in time it gets very tricky to study development as you are limited to whatever fossils survive, which doesn’t always represent the real past (for example, creatures with tough shells like trilobites fossilise a lot better, so it can look like there were more of them then other species just because there are more fossils of them).

      As Nicki mentioned, life is extremely good at adapting to new environments and conditions. Many theories exist on the Cambrian explosion, such as rising oxygen levels supporting larger organisms, and a thicker ozone layer forming that prevented lethal radiation so that more life could develop on dry land.

      Evolution is capable of progressing surprisingly fast given the right driving conditions. For an example relevant to my work, you just have to look at the rise of antibiotic-resistant bacteria and the so-called hospital superbugs. Modern drugs are so effective at killing most bacteria, that the few which develop mutations that let them survive evolve really quickly, and can grow rapidly without competition from other species.

      Evolutionary history isn’t something I know much about unfortunately, so I could be totally wrong. But I imagine the Cambrian explosion was the result of a VERY complicated mix of geological changes causing lots of new conditions for life to rapidly adapt to.

    • Photo: Nikolai Adamski

      Nikolai Adamski answered on 9 Mar 2015:

      As Nicki and Sam have pointed out there are many causes/factors that are thought to have contributed to the Cambrian Explosion (as it’s called). Generally you can say that if the environmental conditions are ‘right’ (and ‘right’ can mean different things depending on the species/organism you are looking at) individuals from a single species can diversify and conquer new habitats or niches: If this new niche turns out to be good for those individuals, they will produce offspring, which will continue to inhabit this new niche. Over time, the offspring of these few individuals will form a new species.

      You can see this even today in cichlids, which is a genus of fish that has rapidly diversified over a short period of time. There are now many different cichlid species living in Lake Victoria and surrounding lakes that once belonged to one species. Individuals from this population adapted to different niches and eventually formed distinct species that look different, eat different food, etc.

      I’m no expert on this, but I hope our answers have helped you.
      cheers
      nikolai

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