For the previous installment, see here.
In 1995, Chinese scientists discovered even older Cambrian fossils near Chengjiang, China. At this site, even more Cambrian phyla and species were uncovered. This discovery also put to death the most popular form of the artifact hypothesis. One can no longer claim that the Pre-Cambrian lacks the Cambrian ancestors because the ancestors were too soft (no exoskeleton) or too small given the fact that the Chinese researchers discovered fossilized sponge embryos which are both microscopically tiny and entirely soft-bodied. They were preserved so beautifully that they were even able to see them in the midst of cell-division and identify the nucleus of the cells. Of course, even before this discovery, we knew that soft-bodied animals could be preserved in the fossil record since filament-shaped micro-organisms had already been discovered in the Precambrian, and many other soft-bodies animals, organs, and anatomical structures in both the Cambrian and Precambrian. According to Simon Conway-Morris, the Burgess Shale (Cambrian) contains 70K+ specimens, and 90% of them are either entirely soft-bodied or have a thin skeleton. The fossils discovered by the Chinese contained even more soft-body animals and preserved eyes, intestines, stomachs (and even the contents in the stomachs), mouths, and nerves. Furthermore, it would be impossible for some ancestors of the Cambrian phyla to function without their hard parts (such as an exoskeleton). They would have to have evolved together, and thus we would expect to find those ancestors in the Precambrian. If the Precambrian could preserve soft, tiny organisms, then why don’t we find the transitional forms leading up to the Cambrian phyla in the Precambrian?
Can the lack of transitional forms throughout the fossil record be explained by incomplete sampling – that we simply haven’t uncovered enough fossils to find the transitions yet? No. We have found an amazing number of fossils, but they always fit in the same place on Darwin’s tree of life: the tips of the nodes. None of the fossils can be placed deeper down the tree at the branching levels to connect the dots.
Some try to deny that there even is a Cambrian explosion by pointing to the Ediacaran fossils in the Precambrian. It’s claimed that these fossils represent the ancestors to the Cambrian phyla. The Ediacaran fossils have been found most famously in Australia, but also in England, Newfoundland, Russia, and Africa – indicative of a global distribution of these animals and fauna.
The Ediacaran fossils appear in the fossil record between 570-565 MYA, and disappear 543 MYA, 13 MY before the start of the Cambrian. Sponges are the oldest of this group. Other types of fossils include trace fossils (fossilized tracks or feces), primitive mollusks, Ediacaran animals, and Ediacaran fauna. Apart from the sponges and mollusks, the animals in the Precambrian bear no resemblance to the Cambrian phyla. Some of them may have been land creatures, and thus cannot be related to the Cambrian phyla (which are all sea creatures). We aren’t even sure if some of them should be classified as animals. At best, the Ediacaran fossils could be related to four of the 20 Cambrian phyla (this includes trace fossils). What about the other 16 phyla? Where are their ancestors?
Rather than solving the Cambrian explosion, the Ediacaran fossils deepen the mystery. First, the Ediacaran represents a mini explosion of its own. For 3 billion years we only have evidence of single-celled life. Then, in a geological blink (15 MY) multi-cellular, complex organisms appear on the scene with no apparent ancestors. How did that happen?
Second, from the start of the Ediacaran to the end of the Cambrian is only 40 MY. If the Ediacaran fossils are ancestral to the Cambrian fossils, how do we explain the radical degree of change that would be required to make that transition in less than 40 MY? It may seem like a long time, but given population genetics, it is not enough time to create such large-scale innovations.
Although there is no evidence of Cambrian ancestors in the fossil record, that hasn’t stopped scientists from trying to identify them. Using the notion of a molecular clock and comparing molecules from different animals, they have determined when the last common ancestor to the Cambrian phyla originated.
The problem with this approach to finding the Cambrian ancestors is multiple. First, this approach cannot be used to establish the existence of ancestral forms to the Cambrian phyla because it merely assumes that there were ancestral forms to the Cambrian phyla to begin with. All these studies show us is how old the last common ancestor would be if there was a last common ancestor. So used as proof for ancestral forms, it is circular argument. For all we know, based on the hard data (the fossil record), there are no ancestral forms to the Cambrian phyla.
Secondly, it assumes the truth of universal common descent.
Thirdly, scientists come up with a wide variety of dates for the date for the last common ancestor depending on which molecules they study. Dates can differ by hundreds of millions of years. This leads to the next problem: subjectivity.
Which molecules scientists choose to base their date on is very subjective. Some molecules, such as histone, do not differ much from organism to organism, so scientists ignore it because it does not yield a date in the Precambrian that fits the theory of Darwinian evolution. Other molecules differ so much that a molecular clock analysis dates the last common ancestor to a time before the Earth existed. Given the fact that different molecules yield different dates, how do scientists determine which molecules give us an accurate picture? It appears that the molecules selected for study are cherry picked to give results consistent with Darwinian evolutionary expectations. In essence, the experiments are being used to support the presuppositions of the scientists conducting them.
Fifthly, these experiments assume that the mutation rate is constant. We know, however, that the mutation rate is different for different animals, and even different for different molecules within animals. So the mutation rate used to calculate the last common ancestor is subjective as well.