Today’s New Reason To Believe

Posted by Fazale ‘Fuz’ Rana, Ph.D.

The 1% Myth

In 1891 Harley Procter commissioned a laboratory to conduct a chemical analysis that would have far-reaching impact. The laboratory determined that only 0.56% of the measured ingredients in a bar of soap failed to fit into the category of “pure soap.” This result led to one of the best-known advertising slogans of all time: Ivory Soap™ “99 44/100% Pure.”

In 1975 Mary-Claire King performed an analysis that also had far-reaching impact. She determined that several human and chimpanzee proteins display a 99% agreement in amino acid sequence. King’s work showed that humans and chimpanzees possess a closer genetic relatedness than anyone at that time had thought. This result has led to one of the best-known cultural icons of our time: “Humans are 99% chimpanzee.”

For many, this genetic similarity represents one of the most compelling arguments for humanity’s evolutionary origin. Presumably, the 99% sequence overlap observed for proteins and DNA indicates that humans and chimpanzees arose from a common ancestor some time in the relatively recent past. Accordingly, the small genetic differences arose after the human and chimpanzee lineages split as a consequence of mutational changes to each species’ genetic material.

(By the way, a high degree of genetic similarity between humans and chimpanzees does not controvert a biblical view of human origins. In fact, Scripture seems to imply that biological similarity exists between humans and other animals, including the Great Apes. (See a recent article I wrote in Connections for a full explanation.)

Even though many evolutionary biologists consider the 99% genetic similarity between humans and chimps as a profound truth, it turns out to be largely useless information. The genetic similarity between humans and chimps doesn’t explain why there is such a fundamental biological and behavioral difference between us and these creatures.

Anthropologist Jonathan Marks addresses this point in his book, What It Means To Be 98% Chimpanzee. Marks maintains that comparisons based on the percent similarity (or difference) of DNA sequences is largely meaningless. As a case in point, he highlights the fact that humans and daffodils possess a 35% genetic similarity. According to Marks,

In the context of a 35% similarity to a daffodil, the 99.44% of the DNA of human to chimp doesn’t seem so remarkable. After all, humans are obviously a heck of a lot more similar to chimpanzees than to daffodils. More than that, to say that humans are over one-third daffodil is more ludicrous than profound. There are hardly any comparisons you can make to a daffodil in which humans are 33% similar.

A recent news focus piece written by John Cohen for Science makes the same point as Marks. The 99% genetic similarity provides limited biological insight, at best. University of California, San Diego zoologist Pascal Gagneux states in the article that

Now it’s totally clear that it’s (the 99% genetic similarity) more a hindrance for understanding than a help.

It turns out that there are numerous features of the human and chimpanzee genomes that differ significantly. And these genetic differences have the potential to account for the biological and cognitive disparities between our species and chimpanzees.

Cohen identifies several key differences between human and chimp genomes that went unnoticed until recently because of the fixation on the 1% genetic difference. For example:

1. The true genetic similarity between humans and chimps is not 99% (which is based on substitution mutations). Instead it’s about 90% when indels (insertions and deletions in the DNA sequences) are considered.
2. Researchers have also discovered that the gene copy number differs for human and chimp genomes. In fact, preliminary data suggests that gene copy number may differ by 6.4% between the two genomes.

Both indels and gene copy number are biologically significant, affecting gene expression.

Thus, the research reveals that humans and chimpanzees are not as genetically similar as popular myth would have us believe. If a 99% genetic similarity implies a close evolutionary relationship, what does a 90% similarity mean?

Nobody would have bought Ivory Soap if it was only 90% pure. Nobody should buy that humans are 99% chimpanzee.

Next week I will discuss another important genetic difference between humans and chimpanzees.

For a detailed discussion of the genetic similarities and differences between humans and chimpanzees and what it means for a human evolutionary and for RTB’s creation model see Who Was Adam?

Posted by Fazale ‘Fuz’ Rana

The 1% Myth

I kept thinking the project was a disaster because I couldn’t find any difference,” Mary-Claire King once mused. Ironically, it was the absence of any difference that made the results of her Ph.D. project so remarkable.

While working at the University of California, Berkeley, in the early 1970s, the burgeoning geneticist compared the amino acid sequences as well as the immunological and physical properties of several proteins isolated from humans and chimpanzees. These three measures all indicated to King and her Ph.D. supervisor, Allan Wilson, that only a small genetic distance separated the two species. (An organism’s genetic material directly specifies each protein’s structure and, hence, physical and immunological properties.) In fact, King uncovered a 99 percent agreement in the amino acid sequences of several human and chimpanzee proteins.

While King felt disappointment with her inability to unmask any genetic or biochemical differences between humans and chimpanzees, the scientific community did not. In fact, Science, one of the world’s most prestigious science periodicals, published the article she co-wrote (with Wilson) on the molecular comparisons between human and chimpanzees as the cover piece for the April 11, 1975 issue?a rare honor indeed.

King and Wilson predicted, at that time, that gene regulation must account for the biological and behavioral differences between humans and chimpanzees. In other words, they did not regard the high percentage of genetic similarity between human and chimpanzee genes as particularly meaningful. (I discussed this point last week.)

In the last few years, scientists have demonstrated that gene expression patterns between humans and chimpanzees differ, particularly with regard to brain tissue. (See Who Was Adam? for a detailed discussion of this work.) This new insight validates the early ideas of King and Wilson.

Two recent studies uncover added evidence for gene expression differences between our species and chimpanzees. One investigation compared gene expression patterns in humans and chimpanzees by looking at both mRNA and protein production and concluded that bona fide differences in gene expression exist for the two primates.

Another study identified differences in the promoter regions of a number of genes in humans and chimpanzees. Promoters are segments of DNA associated with genes that control gene expression. The genes most impacted are those associated with neural activity and nutrition-related functions.

Scientific advance continues to demonstrate that humans and chimpanzees do display significant genetic differences. These differences relate to how the genes are used, not the sequence differences in those genes. The two species differ genetically where it counts. Therefore, to say that a human is 99% chimpanzee is a meaningless statement.

Division of Labor Points to Important Differences between Humans and Neanderthals

A few days before Father’s Day, I saw an ad for Father’s Day gifts under $25. What! Under $25! You would never see an ad for Mother’s Day gifts under $25. In fact, it would border on sacrilege to even consider spending less than $25 on your mother.

Mothers and fathers just aren’t the same. This is probably because they play different roles in our lives.

Anthropologists refer to the different activities of males and females as division of labor. These scientists view this specialization between males and females, and juveniles and adults as a defining feature of modern humans. This behavior promotes robust human economies and allows humans to survive—in fact thrive—in diverse environments.

Evolutionary biologists seek to account for division of labor in modern humans. When did this behavior emerge? Did the hominids that preceded modern humans in the fossil record display this behavior?

From an evolutionary standpoint, division of labor should emerge gradually. The behavior and activities of hominids should increasingly overlap through time with those of modern humans.

RTB’s human origins model—detailed in Who Was Adam?—predicts, however, that behaviors like the division of labor should appear suddenly and be unique to modern humans.

RTB’s Model and the Hominids

RTB’s biblical creation model views the hominids found in the fossil record as animals created by God’s direct intervention. These creatures existed for a time and then went extinct. RTB’s model considers the hominids to be remarkable creatures that walked erect and possessed some level of limited intelligence and emotional capacity. This allowed these animals to employ crude tools and even adopt some level of “culture” much like baboons, gorillas, and chimpanzees. While the RTB model posits that the hominids were created by God’s divine fiat, they were not spiritual beings made in His image. RTB’s model reserves this status exclusively for modern humans.

The model treats the hominids as analogous to, but distinct from, the great apes. Because of this, the RTB model predicts that anatomical, physiological, biochemical, and genetic similarities will exist among the hominids and modern humans to varying degrees. But since the hominids were not made in God’s image, they are expected to be clearly distinct from modern humans, particularly in their cognitive capacity, behavior, “technology,” and “culture.”

A recent study explored the origin of division of labor by comparing the archeological records associated with the earliest modern humans and Neanderthals.

Neanderthals serve as an excellent case study to understand the emergence of this behavior. These hominids appeared late in the fossil record and their existence overlapped with modern humans for a period. They had large brain sizes. Neanderthals established permanent populations and left behind an abundant archeological record.

Based on a detailed survey of the Neanderthal archeological record, anthropologists Steven L. Kuhn and Mary C. Stiner conclude that division of labor among Neanderthals was relatively limited. Neanderthal activity seems to have been focused on pursuing large terrestrial game. Neanderthal foraging practices were restricted to easily collected species. They didn’t exploit plants to any measure. There is no evidence for grinding and crushing implements at Neanderthal sites. Nor is there any evidence that Neanderthals manufactured clothing. These limited behaviors indicate that Neanderthal males and females, both adults and juveniles, must have all been involved in hunting large game.

The behaviors of Neanderthals stand in sharp contrast to the diverse activities of modern humans. The first humans foraged a wide range of creatures, those easy to collect and those requiring some level of ingenuity. Humans hunted a smattering of animals. They fished and made use of plants. They produced a wide variety of tools and manufactured clothing. This assortment of behaviors implies a division of labor among the earliest modern humans.

These differences in behavior have important implications. Because Neanderthals only hunted large game animals, they occupied the top trophic levels in the ecosystem. This placement limited their population sizes to small numbers and made them susceptible to extinction. In fact, Kuhn and Stiner speculate that Neanderthals’ failure to divide labor ultimately led to the creature’s demise.

The hunting and foraging practices of the first modern humans placed them in lower trophic levels. This allowed them to achieve much larger population sizes and made their populations intrinsically more robust than Neanderthals’. Division of labor among the first modern humans allowed them to occupy diverse, novel, and harsh environments. These abilities made modern humans ideally suited to rapidly migrate from their point of origin to fill the Earth.

This study and others highlight the fundamental differences in behavior between Neanderthals (and the other hominids) and modern humans—differences that are in full accord with RTB’s biblical model for human origins.