Tuesday, April 25, 2017

Scientific Evidence and Adam

According to the Bible, all humans stem from Adam (created by God from lifeless clay) and Eve (created by God from Adam's side), who lived less than 10,000 years ago. Mainstream scientists, on the other hand, insist that humans evolved from ape-like ancestors, a few million years ago, with a population size that was never smaller than 10,000. The scientific evidence for this is said to be overwhelming. Consequently, many Christians no longer consider the first few chapters of Genesis to be historical.

Is the alleged scientific case against the Biblical Adam really beyond reasonable doubt?

Fossil evidence
Ideally, if humans evolved from ape-like creatures, one would expect to find a series of ancient fossils reflecting a gradual change from ape-like to human.

However, the fossil evidence is generally problematic for macro-evolution. Most fossil species appear suddenly, fully formed, and then remain virtually unchanged until they disappear. Gradual change from one species to another is not observed.

The situation is even worse for human fossils. Hominin (i.e., ancient ape- or human-like) fossils are very rare, often consisting of mere bone fragments. Moreover, these hominin fossils do not show a gradual transition from ape-like to human-like. Rather, Homo erectus fossils, which are very similar to modern humans, appear abruptly about 2 million years ago (according to mainstream dates). For a detailed discussion I refer the reader to "Human Origins and the Fossil Record" by Casey Luskin (Chapter 3 of Science &; Human Origins, by Ann Gauger, Douglas Axe, and Casey Luskin, Seattle, WA: Discovery Institute, 2012).

The evolutionary biologist Ernst Mayr (1904-2005) commented,
The earliest fossils of HomoHomo rudolfensis and Homo erectus, are separated from Australopithecus by a large, unbridged gap. How can we explain this seeming saltation (JB: "saltation" is an abrupt change)? Not having any fossils that can serve as missing links, we have to fall back on the time-honored method of historical science, the construction of a historical narrative.
[Ernst Mayr, What Makes Biology Unique? Cambridge, UK: Cambridge University Press, 2004, p.198].
Creationists Todd Wood & Joseph Francis, on the basis of their statistical baraminology, concur that human-like fossils are readily distinguishable from animal fossils. They consider Neandertals  and homo erectus to represent populations of humans that dispersed from Babel after the confusion of languages (see their chapter on "Adam and the Animals" in What Happened in the Garden [ed. Abner Chou, Grand Rapids, MI: Kregel, 2016]).

Genetic evidence
Given the shortcomings of fossil evidence, the case for human evolution relies mostly on genetic evidence.

Central to genetics is DNA (deoxyribonucleic acid), the molecule found in the nucleus of every cell. It determines how an organism develops. DNA contains many genes, which are molecular codes for making everything the organism needs, especially proteins. Proteins are large biological molecules that perform various functions within the cell. Humans have about 25,000 genes in each DNA molecule. Genes are packaged in groups called chromosomes.

The human genome is a complete copy of the entire set of gene instructions. Humans have 23 pairs of chromosomes (each chromosome has one copy from each parent). Our offspring get a random selection from each pair of these chromosomes.

In reproduction, the cell needs to make copies of its DNA. Sometimes a copying mistake is made in the sequence of the DNA. This is called a mutation. Evolution assumes that random mutations cause changes in organisms, and that natural selection will weed out bad mutations and further propagate good mutations. In this way, life allegedly evolved from a simple cell to more complicated organisms, and, eventually, to humans.

Comparing the DNA of various species may thus give important evidence of evolution. Similarities and differences in DNA may indicate how closely related various species are to each other.

1. Similarity of humans and chimpanzees
The human genome is closest to that of chimpanzees. How close? Some say that they differ by only about 1%. This is taken as evidence that humans and chimpanzees have a common ancestor.

However, the differences are actual much larger than 1%. This 1% is based on comparing only those stretches of chimp DNA that are similar to human DNA. It ignores those parts of the DNA that are dissimilar [see Don Cohen, "Relative Differences: The Myth of 1%," Science, Vol. 316:1836 (June 29, 2007)].

For example, one study found that many genes in chimps differ totally from those in humans. The study infers that, since the presumed split of humans from chimps, humans gained 689 new genes whereas chimps gained 729 different genes. Thus, merely in terms of genes, humans differ by at least 6% ([689+729]/23,000 = 0.062) [see Jeffery P. Demuth, Tijl De Bie, Jason E. Stajich, Nello Cristianini, Matthew W. Hahn, “The Evolution of Mammalian Gene Families”, PLoS One 2006;1:e85].

Further, the actual genes make up only a few percent of the genome. The rest of the genome is concerned with regulating the genes, turning on switches, and other functions that are not yet fully understood. When the total genome is taken into account, the difference between chimps and humans increases to about 20% [see Jeffrey Tomkins and Jerry Bergman, “Genomic monkey business – estimates of nearly identical human-chimp DNA similarity re-evaluated using omitted data”, Journal of Creation 26(1): 94-100 (April, 2012)].

However, even if humans and chimps are genetically similar, this does not demonstrate common ancestry. Genetic similarity between humans and chimps could be a result of common design. Since humans and chimps have similar bodies, the parts of which have similar functions, they need similar proteins. Hence, one would expect that many genes would be very similar.

2. Sequences of genes and pseudo-genes
Further evidence for evolution comes by comparing similar genes and pseudo-genes (parts of the genome that appear to be genes that have lost their function). By comparing similar genes of various animals, it is thought possible to determine a gene's hereditary line. For most genes, humans are closest to chimps. If humans and chimps actually evolved from a common ancestor, one might expect that chimps would be closest for all similar genes. However, this is not the case: 15% of human genes are closer to gorillas than to chimps [see Kerri Smith, “Gorilla joins the genome club”, Nature, March 12 , 2012]. This challenges the notion that humans evolved from chimps.

3. “Orphan” genes
Many genes in humans have no similar counterpart among apes. Hence, they are called “orphan” genes, since they appear to have no ancestors. As we saw above, humans have 689 orphan genes that are said to have originated after the presumed human-chimp split. These are hard to explain via evolution, which views human genes as modified versions of ancestor genes. The development of an entirely new gene calls for a complete set of scores of good mutations, which has an extremely low probability.

4. Evidence regarding an initial pair
Thus far we have shown that the scientific evidence for human evolution from ape-like creatures is not only ambiguous, but can be interpreted also in terms of common design.

What about the evidence for the notion that humans could not have originated from a single pair?

This claim is based on the currently observed genetic diversity among humans. Humans all have very similar DNA: 99.9% is the same for all people. It is assumed that all diversity comes from random mutations operating on an initially common genome. Estimates of at least 10,000 humans at any time are based on idealized statistical models using assumed mutation rates, random breeding, no migrations, and so on.

However, several recent studies cast doubt on the reliability of these estimates. First, genetic diversity is not necessarily higher in a larger population [see Hans Ellegrin, “Is genetic diversity really higher in large populations?” Journal of Biology 8 (2009): 41]. In cases where the initial population size was known (e.g., Mouflon sheep and Prsewalski's horses), the genetic diversity many generations later was found to be much greater than expected on the basis of the models [see Fazale Rana, Who was Adam?” in More than Myth? P.D. Brown and R. Stackpole (eds.), USA: Chartwell Press, 2014, p.165].

Further, the human genetic diversity could be due to not only mutations, but also to created genetic diversity within an initial pair (Adam and Eve). For example, our DNA has two copies (one from each parent) of each chromosome but one. Our offspring gets a random combination of these chromosomes. If Adam had two different forms of many genes, rather than two identical copies of each, this could explain the human genetic diversity, since most genes have only two different forms.

Along these lines, two recent papers [Genetic Modeling of Human History Part 1 and Part 2 in the Bio-Complexity (2016) journal by Ola Hössjer, Ann Gauger, and Colin Reeves] argue that the genetic data is at least was well explained by a model in where humanity arose from a single couple with created diversity. Moreover, they find that, if the first couple lived in Africa, their model gives old estimates for the age of humanity. However, placing the first couple in the Middle East yields a much younger age.

A more detailed Biblical model has been developed by Robert Carter and Matthew Powell ["The Genetic Effects of the Population Bottleneck Associated with the Genesis Flood", Journal of Creation 30 (2016): 102-111]. They conclude that the genetic data can readily be interpreted in terms of created diversity in a recent Adam and Eve, a later bottleneck where the Flood left only Noah's family, and a subsequent division of the population after Babel.

In short, the scientific evidence from both fossils and genetics by no means rules out the Biblical account of Adam and Eve, nor that of Noah's Flood. All the data can be viewed in terms of scientific assumptions and models that are consistent with what the Bible tells us about history. Hence, theologians should resist elevating the evolutionary story of mainstream science above the plain reading of Scripture.

1 comment:

JohnV said...

Dr. Byl:
Thank you for this summary of the fossil and DNA issues facing the evolutionists. Makes you wonder, doesn't it? If they don't have fossil evidence, and they don't have DNA evidence, then what is it that is so convincing about evolution, especially the line from apes to man, that makes it "overwhelming", or "beyond reasonable doubt"?

It seems to me that a statement such as "How can we explain this seeming saltation? Not having any fossils that can serve as missing links, we have to fall back on the time-honored method of historical science, the construction of a historical narrative"
would have been laughed out of the classroom in days gone by? I recall that my first classes in science were lessons in the use and abuse of logic.

I know what the speaker means. He's saying that "historical narrative" is equal to "possible scenarios that explain the known facts." Well, I can see how a defence lawyer would use this to establish "reasonable doubt", but I can't see a district attorney using this to defeat reasonable doubt. Historical narratives which fill in for a void in evidences are not evidences themselves.