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There are literally millions of examples of interesting side-effects of the evolutionary process. Vestigial organs, advanced behavioral characteristics, development cycles, etc. Here are some examples:
Remnants of alternate gender
In human males, there is a blind duct, called the vagina masculina, attached to the prostate. It is the male vestigial remnant of the female vagina and uterus. All fetuses begin with a set of mullerian ducts. In males, the mullerian ducts don't develop (into a vagina and uterus) because Anti Mullerian Hormone is present. If Anti Muller Hormone isn't present the fetus can be born with Persistent Mullerian Duct Syndrome, which indicates you have an XY male with normal external genitalia, but a malformed or small uterus, upper vagina or cervix developed near the pubic bone.
The female counterpart is the Wolffian Duct, which develops into the prostate, epididymis, vas deferens etc in males, and regresses in females. In female, it can be present either as Skene's glands or as Gartner's Duct.
It's a cool thing to think about, because it means that regardless of actual genes, many intersex conditions are a result of hormone reception and expression (which are related to genetics usually, but occasionally an environment-related issue). A related form of hermaphroditism present in some supermodels is Androgen insensitive hermaphroditism, where an XY male fetus is exposed to testosterone in the womb, but has no receptors for the testosterone or other androgens and develops as a female with external genitalia, but usually lacks a uterus and occasionally has a malformed cervix. These people are women, mentally and identify as female, but a karyotype will show they have an X and a Y.
Cicada life cycle
The cicada life cycle is an example of a really cool evolutionary phenomenon. Some species of cicada emerge from the ground only after 13 years, and some emerge only after 17 years. Both of these are prime numbers. This means that a predator cannot become adapted to preying on cicadas as a food source very easily. For example, a cicada with a 15-year life cycle could be preyed upon by a predator with a three- or five-year life cycle, but the 13- and 17-year cycles allow them to stop the predator life cycle from synchronizing.
Men can lactate
Even though men are almost never ever responsible for breastfeeding their children, evolution hasn't eliminated mammary glands in men, presumably because they do not carry a selection advantage or disadvantage and thus are not acted upon by selection forces.
The diving bell spider
It's basically a spider that makes a kind of "aqua lung"/scuba tank out of its web and uses it to live underwater most of its life even though it uses air to breathe. The diving bell spider uses a special web that actually exchanges oxygen and carbon dioxide through osmosis while underwater and never needs to be refilled to provide breathable air.
Humans arbitrarily claim they're "special"
Humans are forever looking for ways to make their species seem special, by making up stuff like "we are the only species that uses tools" or "we are the only species that can plan for the future". Neither of these are true, but more importantly, these types of things are entirely arbitrary. We think tool usage is important because it makes us special, not the other way around. Not to mention that other animals do make and use tools as well as plan for the future.
Yeast control mutation rate
The molecular basis for evolution is basically typos made while replicating DNA that result in mutations. Complex organisms have sophisticated spell-checkers built in to limit how much this occurs.
Yeast, when put in conditions that are just barely tolerable (temperature or pH off) are actually able to switch off their spell-checkers, deliberately increasing their mutation rate in the hopes of hitting a favorable adaptation.
With the way adaptive immunity works, if a small amount of bacteria infected you and started pumping out toxin, in most cases you'd be immune before the concentration became high enough to harm you.
At some point, Pseudomonas aeruginosa worked this out and began using quorum sensing, basically population-wide chemical signaling, to keep tabs on how many of them there are. They hold off releasing toxin until there's enough of them and then they all flood your system with it at once before your immune system has its boots on.
Race and location
Race is an evolutionary trait and depends on the country of origin.
Africans have darker skin to protect them from danger from the sun's rays. The wider, flatter nasal structure helps the body draw in more moisture in the desert climes. The tighter curls enable the body to give off heat while holding moisture to the skin.
Nordic people have light skin and hair to draw in the sunlight since they need more of the sun's benefits. The smaller nasal structure protects the body from drawing the cold air into the lungs while helping the body retain what moisture it can. The ability to grow long, straight hair acts much like a pelt of a wolf or a woolly mammoth to keep the elements out.
Alternation of plant generations
The earliest plants had two separate and distinct life cycles... a gametophyte, which produces male and female gametes, and a sporophyte, which produces spores. Spores develop into gametophytes, and gametophytes produce gametes that mix and the resulting fertilized egg becomes a sporophyte.
The thing is, this system is still maintained as plants have evolved.
Mosses were the most primitive, since they can't grow to be very large and require water as a medium for the gametes to mix.
The next stage of plant evolution were ferns, which have actual vascular tissue and can therefore stand taller, absorb more sunlight. More importantly, adult ferns produce spores, and these spores mix to make tiny gametophytes and the cycle progresses as normal.
Next stage is pollinating plants. Pollen grains themselves are tiny male gametophytes. The large, adult plant is itself a sporophyte.
Eventually you see flowering plants, which no longer have to expend so much energy to fertilize adjacent plants, and the alternation of generations is maintained.
The above series is an example of how evolution builds on and around a singular system, modifying it as time goes on.
Orca whales speciating
There are at least 3 races/subspecies/species of orca [killer whale]. If they are not separate species yet, we are seeing a step of evolution in progress.
The first type, known as residents, live in coastal waters and feed exclusively on fish. They live in large families and are vocal nearly all the time. They live in very localized areas and only migrate according to where their food source travels.
The second are known as transients. They wander over larger ranges, and eat small marine mammals. They are still a mainly coastal species. They live in smaller groups and are often silent.
The third type are known mainly as offshores, and like their name, prefer deeper oceanic ranges. Why? They prey exclusively on whales. Nearly nothing is known about their social structure.
The three types never ever engage in any kind of social activity or breeding. They are all genetically distinct from each other. Research is currently being conducted to decide whether their differences are enough to warrant separate species status.
Mantis shrimp eyes
Mantis shrimp are the only known animals with hyperspectral colour vision. Their eyes (both mounted on mobile stalks and constantly moving about independently of each other) are similarly variably coloured, and are considered to be the most complex eyes in the animal kingdom. They permit both serial and parallel analysis of visual stimuli.
Each compound eye is made up of up to 10,000 separate ommatidia of the apposition type. Each eye consists of two flattened hemispheres separated by six parallel rows of highly specialised ommatidia, collectively called the midband, which divides the eye into three regions. This is a design which makes it possible for mantis shrimp to see objects with three different parts of the same eye. In other words, each individual eye possesses trinocular vision and depth perception. The upper and lower hemispheres are used primarily for recognition of forms and motion, not colour vision, like the eyes of many other crustaceans.
Rows 1-4 of the midband are specialised for colour vision, from ultra-violet to infra-red. The optical elements in these rows have eight different classes of visual pigments and the rhabdom is divided into three different pigmented layers (tiers), each adapted for different wavelengths. The three tiers in rows 2 and 3 are separated by colour filters (intrarhabdomal filters) that can be divided into four distinct classes, two classes in each row. It is organised like a sandwich; a tier, a colour filter of one class, a tier again, a colour filter of another class, and then a last tier. Rows 5-6 are segregated into different tiers too, but have only one class of visual pigment (a ninth class) and are specialised for polarisation vision. They can detect different planes of polarised light. A tenth class of visual pigment is found in the dorsal and ventral hemispheres of the eye.
The Cacau tree has a symbiotic relationship with the micro-organisms in the soil near it. The cacao tree has some of the most primitive roots in the plant world. Without the micro-organisms assisting the trees roots there would be no chocolate in the world.
Ants take slaves
Ants start wars involving massive numbers and deaths. They even take slaves/POW during battle and force them to do the colony's grunt work.
Seeds needing fire
There are several types of trees and herbaceous plants whose seeds will only germinate after a fire, meaning that the occasional wildfire is necessary. Some species, such as the jack pine, even rely on fire to spread their seeds. The jack pine produces "seratonous" (resin-filled) cones that are very durable. The cones remain dormant until a fire occurs and melts the resin. Then the cones pop open and the seeds fall or blow out.
Birds can't taste hot peppers
Pepper plants (the hot kind) produce a chemical called capsican in their fruit, which causes a burning sensation - but only in mammals. Apparently, natural selection decided that birds spread pepper seeds better than mammals, so capsican developed in the seeds and flesh of the pepper. Birds don't have the chemoreceptors for it to cause the burning, so eating super hot peppers doesn't phase them at all.
Wasps and roaches
A recent study proved using radioactive labeling that the wasp stings precisely into specific ganglia of the roach. She delivers an initial sting to a thoracic ganglion and injects venom to mildly and reversibly paralyze the front legs of the insect. This facilitates the second venomous sting at a carefully chosen spot in the roach's head ganglia (brain), in the section that controls the escape reflex. As a result of this sting, the roach will first groom extensively, and then become sluggish and fail to show normal escape responses. In 2007 it was reported that the venom of the wasp blocks receptors for the neurotransmitter octopamine.
The wasp proceeds to chew off half of each of the roach's antennae. The wasp, which is too small to carry the roach, then leads the victim to the wasp's burrow, by pulling one of the roach's antennae in a manner similar to a leash. Once they reach the burrow, the wasp lays a white egg, about 2 mm long, on the roach's abdomen. It then exits and proceeds to fill in the burrow entrance with pebbles, more to keep other predators out than to keep the roach in.
With its escape reflex disabled, the stung roach will simply rest in the burrow as the wasp's egg hatches after about three days. The hatched larva lives and feeds for 4-5 days on the roach, then chews its way into its abdomen and proceeds to live as an endoparasitoid. Over a period of eight days, the wasp larva consumes the roach's internal organs in an order which guarantees that the roach will stay alive, at least until the larva enters the pupal stage and forms a cocoon inside the roach's body. Eventually the fully-grown wasp emerges from the roach's body to begin its adult life. Development is faster in the warm season.<ewd>http://en.wikipedia.org/wiki/Ampulex_compressa</ref>
- . http://www.bgsu.edu/departments/chem/faculty/leontis/chem447/PDF_files/Jablonski_skin_color_2000.pdf
- . http://www.cals.ncsu.edu/course/ent525/close/SlaveAnt.html
- . http://earthobservatory.nasa.gov/Study/BOREASFire/
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