Home » Biology » Evolution » Scars of evolution

Scars of evolution

Evolutionary baggage = features of organisms that don’t make any sense, given the way that the organism lives today.

Many examples will be discussed here.

One would not initially expect systematic flaws in an organism to exist. Shouldn’t the process of evolution weed out all problems? One also would not expect design flaws if there was an intelligent designer creating life.  Why, then, does evolutionary baggage exist?

Evolutionary theory predicts that they should exist: they came from part of the genome that was advantageous in past individuals, but is disadvantageous under later conditions.

Natural selection is not a perfect process; if an organism is “fit enough” to survive a particular environment and reproduce, its genes are passed on to the next generation. Some of these genes may increase an organism’s fitness while some may even be slightly disadvantageous. This seeming paradox is the origin of evolutionary baggage, which is the collectively inherited traits that evolved in a different environment from the present.

The mammalian eye

An overview of how eyes has evolved is shown below:

{ http://en.wikipedia.org/wiki/Evolution_of_the_eye }


Defects from this process are illustrated here:

Image from: Evolution of the Eye, Scientific American, Trevor D. Lamb, July 2011

Eye Scars of Evolution scientificamerican0711-64-I4

{ Wikipedia contributors. “Evolutionary baggage.” Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 20 Dec. 2013. Web. 2 Jan. 2015. }

Crossover between respiratory and ingestion tubes

“Adapting an ancestral fish into a land dwelling mammal necessarily involved many changes of function and led to some elements of poor design, such as the crossover between respiratory and ingestion tubes resulting in a maladaptive lung/esophagus arrangement (one that leads to almost 3,000 choking deaths in America each year). “


Type I diabetes

It has been hypothesized that genetically-linked type I diabetes was advantageous during the extreme cold temperatures of the Ice Age 14,000 years ago. Type I diabetes would have conferred an advantage for individuals to survive extremely cold temperatures; this condition prevents production of insulin, keeping blood sugar levels high in the blood, which lowered the freezing point of the blood and protected the individuals with the condition.

Vestigial structures

Leftover parts of anatomy that have no function now, but did have a function when the organism existed millions of years ago. Examples include:

* Wings on flightless birds

* Eyes in cave-dwelling animals that are blind

* The pelvis in snakes such as the python. While snakes today don’t have hips and legs, their ancestors did, as their ancestors were four legged.

* Dandelions reproduce without fertilization, yet they retain flowers and produce pollen – both are plant sexual organs normally used for sexual fertilization.

* Flightless beetles which retain perfectly formed wings, housed underneath fused wing covers.

* Human wisdom teeth

Our ancestors were largely herbivorous: molar teeth are required for grinding plant material. Over 90% of all adult humans develop third molars (otherwise known as wisdom teeth). Usually these teeth never erupt from the gums, and in one third of all individuals they are malformed and impacted. These useless teeth can cause significant pain, increased risk for injury, and may result in illness and even death. But these teeth played a role many generations ago.

* Tooth enamel genes – in animals that don’t have teeth.

Jerry Coyne writes:

new paper in PLoS Genetics continues the search for predicted dead genes — this time for genes that once made tooth enamel — and finds a lot of these wrecks. They’re exactly where you expect to find them — in toothless animals long thought to have descended from animals with teeth. So the “theory” of evolution is once again confirmed, although we hardly need further confirmation. But this paper goes beyond a mere redundant proof of common ancestry. The authors also make models of how the “enamel” genes degenerated, and, by calculating when this degeneration happened, predict what the teeth of common ancestors should look like. This prediction is in principle testable by finding the relevant fossils and looking at their teeth.,

* Human tail bone –  the coccyx.

This is made from four fused vertebrae at the base of the spine, which is exactly where most mammals and many other primates have external tails. Humans and other apes are some of the only vertebrates that lack an external tail as an adult. The coccyx is a remnant of the embryonic tail that forms in humans. Our internal tail is unnecessary for sitting, walking, and elimination.


An atavism is the reappearance of a lost character, which used to be part of a distant evolutionary ancestor. An atavism is not observed in the parents or recent ancestors of the organism.  They have several essential features:

(1) presence in adult stages of life,
(2) absence in parents or recent ancestors, and
(3) extreme rarity in a population


* Living whales and dolphins with rear legs! Here are the hind-flippers of a bottlenose dolphin found in Japanese coastal waters.

hindf lippers

* Humans born with tails.

X-ray image of an atavistic tail found in a six-year old girl.


human tail

from talkorigins.org/faqs/comdesc


%d bloggers like this: