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The Fossil Record of the Cambrian “Explosion”: Resolving the Tree of Life

Geologist Keith Miller examines the "Cambrian Explosion", a period of rapid evolutionary diversification approximately 575 million years ago, and whether it poses a challenge to evolutionary theory. From the June 2014 issue of Perspectives on Science and Christian Faith from the American Scientific Affiliation.

 

What scientific evidence do we have about the first humans?

In recent decades, scientists have discovered more about the beginnings of humanity. The fossil record shows a gradual transition over 5 million years ago from chimpanzee-size creatures to hominids with larger brains who walked on two legs. Later hominids used fire and stone tools and had brains as large as modern humans. Fossils of homo sapiens in east Africa date back nearly 200,000 years. Humans developed hearths for fire, stone points for spears and arrows, and cave paintings by 30,000 years ago. By 10,000 years ago, humans had spread throughout the globe. Genetic studies support the same picture. Humans share more DNA with chimpanzees than with any other animal, suggesting that humans and chimps share a relatively recent common ancestor. Also, the same defective genes appear in both humans and chimps, at the same locations in the genome—an observation difficult to explain except by common ancestry. Genetics also tells us that the human population today descended from more than two people. Evolution happens not to individuals but to populations, and the amount of genetic diversity in the gene pool today suggests that the human population was never smaller than several thousand individuals. Yet all humans, of all races, are descended from this group. Humanity is one family.

 

Evolution and the Origin of Biological Information

In this paper, Venema explores several examples in biology where random mutation and natural selection have indeed led to substantial increases in biological information. The question of how new specified information arises in DNA, far from being an “enigma”, is one of great interest to biologists.

 

Does the Cambrian Explosion pose a challenge to evolution?

The “Cambrian Explosion” refers to the appearance in the fossil record of most major animal body plans about 543 million years ago. The new fossils appear in an interval of 20 million years or less. On evolutionary time scales, 20 million years is a rapid burst that appears to be inconsistent with the gradual pace of evolutionary change. However, rapid changes like this appear at other times in the fossil record, often following times of major extinction. The Cambrian Explosion does present a number of interesting and important research questions. It does not, however, challenge the fundamental correctness of the central thesis of evolution.

 

How can evolution account for the complexity of life on earth today?

A complex biological structure with many interacting parts might appear, at first glance, as if it were originally created in its present form with all its interlocking components fully formed and intact. It doesn’t seem possible that they developed step by step via biological evolution. In Darwin’s Black Box, Michael Behe introduces a term that he and other proponents of Intelligent Design use for this concept: irreducible complexity.

 

Does thermodynamics disprove evolution?

A common argument against biological evolution is that the theory contradicts the second law of thermodynamics. The second law says that disorder, or entropy, always increases or stays the same over time. How then can evolution produce more complex life forms over time? The answer is that the second law is only valid in closed systems with no external sources of energy. Since the Earth receives continual energy from the Sun, the second law does not apply.

 

What does the fossil record show?

Fossils provide a unique view into the history of life by showing the forms and features of life in the past. Fossils tell us how species have changed across long periods of the Earth’s history. For instance, in 1998, scientists found a fossil showing an animal at the transition from sea creature to land creature. This tetrapod had a hand-like fin, confirming a prediction of evolutionary biology. Though the fossil record does not include every plant and animal that ever lived, it provides substantial evidence for the common descent of life via evolution. The fossil record is a remarkable gift for the study of nature.

 

What is evolution?

Evolution is the biological model for the history of life on Earth. While some consider evolution to be equivalent to atheism, BioLogos sees evolution as a description of how God created all life. Evolution refers to descent with modification. Small modifications occur at the genetic level (in DNA) with each generation, and these genetic changes can affect how the creature interacts with its environment. Over time, accumulation of these genetic changes can alter the characteristics of the whole population, and a new species appears. Major changes in life forms take place by the same mechanism but over even longer periods of time. All life today can be traced back to a common ancestor some 3.85 billion years ago.

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