EVOLUTION

Snakes, Spiders and Evolution (Oh My!)

ginkoIn the field of evolutionary psychology, the belief is that instinctive fears become hard-wired in our biology through genes or other inheritance. A new study suggests that the fear of spiders and snakes has been shaped by evolution, stretching back to a time when early man slept on the ground or in caves and had to survive in an environment dominated by arthropods and reptiles.
Certain stimuli are pre-wired in the brain because they have been perennially dangerous to our ancestors. Although some of us fear snakes more than others, baby humans, chimps and monkeys are equally jumpy when confronted with a black plastic snake. That aversion probably grew out of pressures of life in the jungles and savannas of Africa eons ago. Back then, encounters with poisonous snakes or spiders were a matter of life or death, and a healthy fear of snakes helped our ancestors live long enough to procreate.
Ginkgo: A Living Fossil

ginkoThe Ginkgo tree is a living fossil. The speed and direction of evolutionary change can vary in a species, allowing some to remain relatively unchanged for long periods of time. Newly found specimens of Ginkgo grew more than a hundred million years ago and are remarkably similar to present-day trees. There are some specimens of Ginkgo in a Chinese monastery garden that are over three thousand years old. Previous fossils have revealed the Ginkgo tree has remained unchanged for over 51 million years, and similar trees were alive and well 170 million years ago, during the Jurassic period. Although there are subtle differences in specimens from the Jurassic period, there is little doubt that this tree is a descendant of forebears that provided food for dinosaurs.

SarahIs That Salad Dressing I Smell?

Bugs. Creepy crawlies. Beasties. Those little critters with exoskeletons- otherwise known as arthropods. The group that includes insects, like bumblebees and cockroaches, arachnids, like spiders and scorpions, and myriapods, like centipedes and millipedes.

Most bugs are little. Even the ones we think of as being big, like tarantulas or luna moths, are pretty little compared to us and most animals. So if you’re a bug, one thing you have to worry about is that there are probably big animals out there who want to catch you and eat you for lunch. To address this problem several bugs have evolved a lot of really clever ways to stay safe from all those big, hungry animals. Some bugs can run really fast, some are camouflaged, and some have painful stingers. And then there are bugs that have truly unique forms of self-defense.

One bug that has evolved a distinctive way of protecting itself is a vinegaroon, or whip scorpion. Vinegaroons are arachnids, which means they have eight legs, two body parts and no antennae. They look quite similar to true scorpions, except they’re missing the thick tail with the stinger at the end, and they’re missing the scorpion’s venom that’s in that stinger. Instead, vinegaroons have a flagellum (a thin whip-like appendage – but from this point on we’ll just call it a tail) that they use as a feeler because they don’t have very good eyesight.

vinegaroonVinegaroons have a gland in their abdomens that produces a solution that is mainly acetic acid. Acetic acid is the same acid that’s in vinegar. That’s right – vinegar. When a vinegaroon feels alarmed or threatened by the presence of a predator, it secretes some of this solution from the base of its tail.

Now, you may think of vinegar as a tasty ingredient in Italian salad dressing and dill pickles. But in the wild, animals don’t eat salad dressing or dill pickles, and when an animal gets a spray of vinegar in its face, it doesn’t like it very much. It doesn’t like the smell, it doesn’t like the taste, and it doesn’t like the burning that results if the acid gets in its eyes. And if the predator is another arthropod, it doesn’t like the feel of the acid seeping through its exoskeleton. So it may just decide to leave the vinegaroon alone and go in search of more appetizing prey. That little spray of acetic acid is a very effective evolved deterrent against danger.

So if you’re ever walking around on a summer night in the southwest United States or Mexico and come across a vinegaroon, and you suddenly smell vinegar, you’ll know the critter isn’t happy about meeting you. But, don’t take it personally. To the vinegaroon, you’re just another huge, hungry animal.

by Sarah Rollin Naughton
Arachnid, Arthropod & Reptile Specialist: Outreach Educator, Philadelphia Zoo
Environmental Educator, Churchville Nature Center

On Common GroundOn Common Ground

The story of our evolution began in Africa about six million years ago and it describes the very long process that our ancestors went through to ultimately become modern humans. Scientists believe that our common ancestor existed 5-8 million years ago. At that time, two species broke off into separate lineages, one ultimately evolving into gorillas and chimpanzees, the other into early humans called hominins.

In the millions of years that followed, at least a dozen different species of humanlike creatures have existed and are reflected in fossil discoveries, although many of these are close relatives and not actual ancestors of modern humans. It is important to remember the line of ancestry does not represent a straight line to us. Many of these early hominids left no descendants and simply died out. Still, others are very likely direct ancestors of modern humans. While scientists still do not know the total number of hominid species that existed, because new fossils are continually being discovered, the story of human evolution becomes clearer all the time.


Video written by Nicole Reggia, Produced by Dave Bock, Now That's Wild.com

Horse Evolution - The evolution of the horse occurred over a period of 50 million years, transforming the small, dog-sized, forest dwelling Eohippus into the modern horse.

DolphinsDecoding Dolphins

The ancestor of today's dolphin appeared on Earth about 95 million years ago. Mesonix was a terrestrial animal that waded into shallow water to feed, had four legs and a body covered with hair. In the next 20 million years, Mesonix adapted to living in the water and forelegs became pectoral flippers while hind legs began to disappear. Vestigial hind limbs are still present in modern day dolphins in the form of rod-shaped pelvic bones and pectoral flippers house all the carpal and metacarpal bones of hands like yours and mine. As a result of evolution, the nostrils of early dolphins migrated from the nose to the top of the head to make it easier to breath while swimming or resting in the water.

The Tokyo Institute of Technology recently decoded the DNA sequences of the dolphin genome showing that these whales are closely related to cows, giraffes, pigs and antelope, with the closest being the hippo. The dolphin's 3-chambered stomach functions the same way as the 4-chambered cow's, providing more evidence of their link. Dr. David Busbee of Texas A & M University has discovered that dolphins and humans share many similar chromosomal similarities. Dolphins and whales have an excellent fossil record and they are one of the best examples of evolutionary transition showing their movement from land to water.

Charles Darwin

In October 1831, the 90-foot vessel named the HMS Beagle set sail for a 5 year voyage around the world that would inspire a young Charles Darwin to transform his thinking into developing his ideas of evolution to explain biological change.

Darwin's exposure to specimens all over the globe led him to believe that they had gradually evolved from common ancestors. The concept of evolution means that species change over time and that over long, and sometimes short, periods generations of plants and animals can look very different due to genetic changes.

Perhaps no one has influenced our knowledge of life on Earth as much as this English naturalist because his ideas about evolution by natural selection made us rethink our place in the world and united us with all life on our planet.

"from so simple a beginning endless forms most beautiful and most wonderful have been and are being evolved"
Charles Darwin - On the Origin of Species by Means of Natural Selection, 1859

Frequently Asked Questions About Evolution

Isn’t evolution just a theory?

When scientists use the word theory, it has a different meaning than normal everyday use. In science, a theory is not a guess or a hunch. It is a well-supported, well-documented, and well-substantiated explanation for observations. For example, the theory of gravity does not mean it is just a guess. It has been tested and all observations support it. You can observe it for yourself, too. Theories in science are never proven. They stand until something proves them wrong. Evolution has been tested in thousands of experiments and has stood the test of time ever since Darwin presented it over one-hundered and fifty years ago. Advances in physics, molecular biology, geology, genetics and chemistry have refined, supported and expanded evolutionary concepts beyond anything Darwin could have imagined.

Are all species related?

NTW PalmYes. All organisms, both living and extinct, are related. In the tree of life, every branch represents a species and every fork separating one species from another represents the common ancestor shared by these species. Scientists are able to sequence DNA and fossils and find descendants joining their ancestors. DNA analyses show that although humans share far more genetic material with our fellow primates, we still have more than 200 genes in common with bacteria. You share genes with yeast, flies, worms, mice and with the cotton fibers in the shirt you’re wearing.

Is there a “missing link”?

NTW Skull PhotoThe idea of a "missing link" is a misconception because nothing is actually "missing". There are many, many transitional forms that have been found between all kinds of distinct taxonomical groups, including in our ancestral line. The news is filled almost daily with new discoveries that show the transitions and adaptations of species. There are many well preserved fossils that show the transitions of things like scales to feathers and toes to hooves and they are on display in museums for everyone to see and study. DNA sequencing has provided further evidence with adaptations occurring at the right time in the geographical record to support these transitions. Several discoveries within our own human lineage fulfilled the predictions that humans share a common ancestor with modern African apes, like the gorillas and chimpanzees.

What is natural selection?

NTW Black SwallowtailNatural selection is the process by which species adapt to their environment and form a new, separate species. It leads to evolutionary change when individuals with certain characteristics have a greater survival or reproduction rate than other individuals in a population and pass these inheritable genetic characteristics to their offspring. The idea of "survival of the fittest" is a misconception. It is more like "survival of the fittest for the times" and even then the so called "fittest" may not be the one to survive. Many things like disease, climate, geography, resources and predation can all determine what traits get passed on to future generations. It is important to remember that natural selection does not produce a straight line to perfection which is evident because most of life that existed on Earth is extinct. Natural selection can take a long time and can only make improvements on the existing models of life.

Does sex play a role in evolution?

NTW Role of Sex in EvolutionYes. Sexual selection allows an organism to combine half of its genes with the half of another and these new combinations of genes are passed to the following generations. It is this genetic diversity that provides the opportunity for a species to change over time. Sexual selection is a very powerful drive in organisms. Peacocks, for example, produce and maintain beautiful, extravagant feathered trains to attract mates. These feathers are harmful to the individual bird’s survival and are likely to attract predators as well as interested members of the opposite sex and they slow down the male birds in fighting, fleeing and flying. Studies have shown that peahens select and mate with peacocks with the biggest tails that advertise the fitness level of their genes.

What is speciation?

NTW SpeciationSpeciation is the progress of how one species splits into two different, distinct species which no longer can interbreed with each other. Speciation occurs when a group within a species separates from other members of its species and develops its own unique characteristics. The demand of a different environment can differentiate the new species from its ancestors. It is important to remember that populations of species evolve, rather than individuals. Although it can sometimes be a slow process, speciation provides and helps to explain the vast amount of diversity we see on our planet.

What is the relationship between time and evolution?

NTW Time & EvolutionIf you wanted to squeeze the 3.5 billion years of the history of life on Earth into a single minute, you would have to wait about 50 seconds for multicellular life to evolve, another four seconds for vertebrates to invade the land, and another four seconds for flowers to evolve- and only in the last 0.002 seconds would "modern" humans arise. It can take many generations to produce the changes over time that we see in plants and animals. Most, but not all, of this change takes place over thousands of years. It is sometimes hard to grasp these long time spans of change because of our own limited time on Earth.


 

NTW Refute the presence of God?Does evolution refute the presence of God?

No. Evolution is a science, not a belief system. Like all science and theories, evolution deals with testable events, objects and processes in the material world. Science does not deal with people’s spiritual beliefs.

Back to Top Now That's Wild Jacques Monod Quote
A curious aspect of the theory of evolution is that everybody thinks he understands it.
-Jacques Monod