Atavism refers to the reappearance of a trait in an organism after several generations of absence. The word atavism comes from the Latin atavus, meaning “ancestor” or “forefather”. In evolutionary biology, an atavism is an evolutionary throwback resulting in the reemergence of a trait in an organism after a period of absence. Atavisms can occur when genes for previously existing phenotypic features are preserved in DNA, and these become expressed through a mutation that either knocks out the suppressing genes for the trait or makes the required genes for the trait over-express themselves.
Examples of Atavism
Some examples of atavisms in humans include:
- Extra nipples or breasts – Some people are born with extra nipples along the milk lines or even extra breast tissue. This is thought to be an evolutionary leftover from our early mammalian ancestors who had multiple nipples for their large litters.
- Wisdom teeth – Our hominin ancestors had larger jaws with more teeth, which have been reduced in modern humans. However, some people still develop these vestigial third molars, or wisdom teeth, which no longer fit in our smaller jaws.
- Coccyx/tailbone – The coccyx or tailbone is remnants of a vestigial tail from our primate ancestry. While modern humans do not develop actual external tails, some babies are born with a vestigial tail due to atavism.
- Goosebumps – When our hairy ancestors were cold or frightened, their hair stood on end and this made them appear larger and more threatening. Goosebumps serve no real purpose in modern humans, yet the reflex remains.
- Darwin’s tubercle – A bump on the rim of some people’s outer ear is thought to be leftover from a joint that allowed the ears to swivel independently in extinct mammalian ancestors.
- Plantar grasp reflex – Infants can curl their toes and grip tightly to cling to their mother’s body as she moved. This reflex disappears around 2-3 months but reappears through atavism in some adults.
- Palmaris longus – A long tendon in the wrist used by primates for hanging and swinging through trees. Around 11% of humans still have this tendon even though it serves no real purpose.
Other examples of atavisms include chickens with teeth, whales with hind leg bones, and humans born with true tails. Even genetic throwbacks to extinct traits like fur, claws, or gills can reappear through atavistic mutations.
Atavism and the Bible
The Bible does not directly address the concept of atavism or evolutionary throwbacks. However, some verses are relevant when considering the implications of atavism for the creation/evolution debate and the fixity of species:
Genesis 1:24-25 – And God said, “Let the earth bring forth living creatures according to their kinds—livestock and creeping things and beasts of the earth according to their kinds.” And it was so. And God made the beasts of the earth according to their kinds and the livestock according to their kinds, and everything that creeps on the ground according to its kind. And God saw that it was good.
This implies God created animal kinds with the ability to reproduce and fill the earth with their kind. Atavisms demonstrate that ancestral genes can reemerge, suggesting a common ancestry for certain traits.
Genesis 1:27 – So God created man in his own image, in the image of God he created him; male and female he created them.
Humans were created specially in God’s image, not through an evolutionary process. Yet atavisms reveal latent evolutionary remnants in humans like tails, wisdom teeth, and other “primitive” structures.
1 Corinthians 15:39 – For not all flesh is the same, but there is one kind for humans, another for animals, another for birds, and another for fish.
This verse distinguishes between basic kinds/types of flesh, not transitional species. Atavisms blurs the line between ancestral and modern traits.
Overall, atavisms showcase genetics’ complexity and latent potentials. Allowing for emergence of ancestral traits could be interpreted as either divinely pre-programmed adaptive mechanisms or as evidence for universal common descent. Atavism highlights lingering questions regarding the fixity of species and whether changes over time are guided by God’s design or natural selection.
Causes of Atavism
There are several proposed causes for atavistic traits reappearing after generations of dormancy:
- Throwback mutations – Novel mutations may accidentally turn back on previously dormant ancestral genes, allowing ancestral phenotypes to reemerge. Errors in DNA copying could lead to atavistic mutations.
- De-repression of ancestral genes – Evolved regulatory processes may repress ancestral genes not needed for an organism’s current environment. Changes relax this repression, permitting ancestral gene expression and atavistic traits.
- Hybridization – Interspecies breeding may allow crossing over of DNA, causing ancestral genes to be expressed in hybrid offspring and produce atavistic traits.
- Pluripotency – Master regulatory genes controlling embryonic development and differentiation may become re-activated, producing reemergence of ancestral traits from early developmental stages.
- Reverse evolution – When an ancestral phenotype provides an adaptive advantage to a species, populations may undergo reverse evolution through selectively retaining ancestral traits and genotypes.
The precise mutations leading to atavism depend on the trait involved. However, atavisms reveal that even though ancestral phenotypes may not be expressed for generations, the genetic blueprints remain in an organism’s DNA. Changing circumstances can permit re-expression of ancestral genotypes that were silenced but not lost from a lineage.
Atavism and Genetic Ancestry
The existence of atavisms provides evidence for evolutionary models of common descent. Atavisms imply that ancestral traits are not completely eliminated but rather are silenced or suppressed through gene regulation or loss of function mutations. Related species share extensive DNA homology and suppressed remnants of common ancestry. Under certain conditions, these ancestral remnants spontaneously reemerge through mutations causing atavism.
This shared genetic toolkit of conserved ancestral genes supports evolutionary relatedness between organisms. For example, birds still carry the necessary genes to produce teeth, just like their reptilian ancestors. With the right mutation, ancestral teeth-generating genetic pathways could reactivate and produce a modern bird with teeth. This latent potential for expressing ancestral phenotypes that are normally silenced in derived species provides a compelling case for their shared evolutionary ancestry.
Atavisms also provide opportunities to examine the evolution of lost structures. Observing how certain genes mutate and reactivate to produce an atavistic trait allows deeper study of that trait’s ancestral form and evolutionary history. For example, studying mutated genes triggering hind limb buds in whales provides insight into how hindlimbs originally developed in ancestral four-legged land mammals. The atavistic return of a lost structure essentially replays evolution in reverse. This offers a powerful demonstration of how incremental genetic changes over time can produce major evolutionary transformations.
Challenges Presented by Atavism
While atavisms provide compelling molecular evidence for biological evolution through common descent, they also present challenges for evolutionary theory:
- Discontinuous nature – Atavisms represent sudden jumps back to ancestral states, whereas evolution normally progresses slowly and gradually through each intermediate stage.
- Lack of adaptive value – Many atavistic traits like tails in humans confer no obvious adaptive benefit and appear maladaptive in the modern context.
- Non-directionality – Atavism represents reverse evolution rather than progressive, forward evolution toward increasingly complex forms.
- Origins of novelty – Atavisms involve reemergence of primitive traits through pre-existing genetic pathways rather than evolution of novel, complex structures.
- Developmental constraints – Expressing an atavistic phenotype may be constrained by the current ontogeny of an organism’s development.
Additionally, some argue atavisms challenge notions about the fixity of species and whether species can change over time into completely new forms. If suppressed ancestral traits can reappear, how malleable are species boundaries?
Proponents of evolution counter that atavisms are exceptions demonstrating the overall stability and continuity of phenotypes under most conditions. They do not fundamentally challenge modern evolutionary theory but rather provide deeper insight into genetic mechanisms influencing evolutionary change. Both sides agree that atavism provides compelling evidence for dormant ancestral genes within species’ genomes.
Atavism and Creationism
For scientific creationists, atavistic traits present in organisms argue against universal common descent from single ancestral forms. Instead, they claim it reflects intentional reuse of efficient design features by an intelligent Creator. The atavistic reemergence of ancestral traits supports special creation of basic biblical “kinds” sharing common designs rather than a universal evolutionary tree of life.
Creationists view atavistic reuse of complex traits like flight feathers in flightless birds as purposeful activation of dormant genetic modules. This opposes the neo-Darwinian view of randomly arising mutations and selective retention generating novel complex structures gradually over time. To creationists, atavism demonstrates an omniscient Creator’s foreknowledge to encode multipurpose adaptive mechanisms able to be reactivated when needed.
Some creationists even argue that suppression and reemergence of ancestral genes aligns with biblical notions of devolution – the gradual deterioration and loss of information since the Fall. They claim well-designed, complex ancestral creatures have degenerated into more specialized but degraded descendants through accumulation of mutations. Atavism occurs when regulatory mutations unlock suppressed ancestral genes, demonstrating that no new functional genetic information arises in descendant organisms.
However, most mainstream scientists counter that there are clear evolutionary pathways for atavisms reactivating silenced ancestral genes that confer modified benefits in different selective contexts. They argue complex novel traits do gradually arise through incremental mutation and selection rather than sudden expression of fully-formed dormant traits. For both camps, atavism provides interesting examples of how organismal form and function arise through genetic variation over generations.
Theological Implications of Atavism
For religious traditions with a high view of humanity, human atavisms may seem theologically problematic. Tails, extra nipples, and other ancestral throwbacks evoke continuity with “lower” animal forms over time rather than special creation. Yet scientifically examining biological quirks can still glorify God through revealing the sophistication of creation.
Atavisms display the intricate balancing act of biological development, reminding that while humans are imago Dei we remain dusty creatures. Our weaknesses manifest through atavism point to utter dependence on God’s grace for wholeness. Additionally, atavism highlights the universal human struggle against sin’s degradation – the tendency toward disorder rather than perfection. Scripture attests that the “whole creation groans” (Romans 8:22) – including our genomes – awaiting final redemption.
Some theologians even posit pre-Fall humanity may have exhibited more fluidity between its spiritual and animal natures. The embarrassment many feel over useless atavistic traits reflects post-Fall dualistic thinking in contrast to original shalom. These vestiges in creation, including human atavisms, instill longing for ultimate restoration through Christ (Colossians 1:15-20). When reconciled to God and each other, perhaps atavisms’design oddities will spark rejoicing rather than shame.
Atavisms also display God’s ingenuity in weaving together old and new (Matthew 13:52). Why might the Creator interlace latent ancestral potentials within organisms? Perhaps atavisms speak to the continuity of earthly and heavenly existence, where all that was good is gathered up and transformed. Or maybe atavisms remind that God “makes all things new” (Revelation 21:5) through poetic reuse rather than ex nihilo creation. By interweaving past and present, atavisms proclaim the Creator’s sovereignty through time.
Ultimately atavisms, along with all creation, disclose glimpses of the divine nature (Romans 1:20). There are no true evolutionary throwbacks – only unfolding revelations of the Creator’s character. Every godly curiosity pursued in biology and beyond can illuminate the wonders of the Almighty.