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What are reasons we know insects evolved on land rather than water


I am reading up on the evolution of insects, and insects supposedly evolved on land rather than water. How do people know?What evidence is there that insects evolved on land and not water?


The sister group of hexapods (Insects plus Collembola, Protura, and Diplura) are thought to be Remipedes. Remipedes are cave-dwelling aquatic pancrustaceans. The most recent common ancestor of Hexapoda and Remipedia was likely aquatic. But somewhere along the pathway to becoming modern hexapods, after they split from the lineage leading to modern remipedes, the ancestors of modern hexapods developed tracheal respiratory systems that function on land. So the evidence comes from the fact that the extant lineages of insects, close to their most recent common ancestor, including Collembola, Protura, Diplura, Archeaognatha, and Zygentoma are all terrestrial.


What are reasons we know insects evolved on land rather than water - Biology

Like other sarcopterygians, the coelacanth has "lobe-fins," muscular fins with a single bone that articulates with the rest of the body. Most fishes (the Actinopterygii, or ray-finned fishes) have several bones at the bases of their pectoral fins, and their fins are composed of a set of webbed rays, not muscle- and skin-covered bone.

Tetrapods evolved from a group of organisms that, if they were alive today, we would call fish. They were aquatic and had scales and fleshy fins. However, they also had lungs that they used to breathe oxygen. Between 390 and 360 million years ago, the descendents of these organisms began to live in shallower waters, and eventually moved to land. As they did, they experienced natural selection that shaped many adaptations for a terrestrial way of life. Like other terrestrial sarcopterygians, modern humans still carry the evidence of our aquatic past in the way our arms and legs attach to our bodies, as well as in the many other features that link us to our fishy origins.

Which came first, the gill or the lung?
Since fish appear in the fossil record earlier than the clade we call tetrapods does, it's tempting to assume that modern fishes bear the same traits that their and our common ancestor did. This line of reasoning is intuitive, but it is not correct. Though it is true that both modern ray-finned fishes and the ancestor we tetrapods have in common with them are finned and aquatic, the same pattern of reasoning does not hold water when it comes to lungs.


The Beguiling History of Bees [Excerpt]

Excerpted with permission from A Sting in the Tale: My Adventures with Bumblebees, by Dave Goulson. Available from Picador. Originally published in Great Britain by Jonathan Cape, a division of Random House Group, Ltd. Copyright © 2014.

Let us travel back in time 135 million years. The vast supercontinent of Gondwana was beginning to break up, with South America drifting off to the west of Africa, and Australia moving majestically off to the east. Antarctica decided to head south, dooming all but the most adaptable of its inhabitants to an eventual icy grave. The South Atlantic and Indian Oceans were slowly forming.

At this ancient time, an era known to geologists as the Cretaceous, the continents were clothed in green forests of tree ferns, cycads, huge horsetails, and conifers such as pines and cedars. This was the height of the reign of the dinosaurs, although not the species that are so well known to schoolchildren the world over: amongst the trees, herds of vast herbivores such as Iguanodon grazed, standing on their hind legs to reach higher foliage heavily armoured, tank-like species such as Gastonia bulldozed through the undergrowth and packs of ferocious meat-eaters such as Utahraptor hunted their prey. The air swarmed with primitive insects including oversized dragonflies and early butterflies, and this was also the heyday of the pterosaurs, the largest animals ever to fly above the earth, with wingspans up to 12 metres. Much smaller dinosaurs had also taken to the air feathers, probably first evolved to help these little creatures keep warm, became elongated on their forelegs to allow gliding and, eventually, active flight. These were the first birds. Our own ancestors at this time were rather unimpressively small, rat-like creatures skulking in the undergrowth, nervously coming out at night to nibble on insects, seeds and fallen fruit. If we could travel to this ancient land, we might be too concerned with the dangers posed by the larger wildlife to notice that there were no flowers no orchids, buttercups or daisies, no cherry blossoms, no foxgloves in the wooded glades. And no matter how hard we listened, we would not hear the distinctive drone of bees. But all that was about to change.

Sex has always been difficult for plants, because they cannot move. If one cannot move, then finding a suitable partner and exchanging sex cells with them poses something of an obstacle. The plant equivalent of sperm is pollen, and the challenge facing a plant is how to get its pollen to the female reproductive parts of another plant not easy if one is rooted to the ground. The early solution, and one still used by some plants to this day, is to use the wind. One hundred and thirty-five million years ago almost all plants scattered their pollen on the wind and hoped against hope that a tiny proportion of it would, by chance, land on a female flower. This is, as you might imagine, a very inefficient and wasteful system, with perhaps 99.99 per cent of the pollen going to waste &ndash falling on the ground or blowing out to sea. As a result they had to produce an awful lot.

Nature abhors waste, and it was only a matter of time before the blind stumbling of evolution arrived at a better solution in the form of insects. Pollen is very nutritious. Some winged insects now began to feed upon it and before long some became specialists in eating pollen. Flying from plant to plant in search of their food, these insects accidentally carried pollen grains upon their bodies, trapped amongst hairs or in the joints between their segments. When the occasional pollen grain fell off the insect on to the female parts of a flower, that flower was pollinated, and so insects became the first pollinators, sex facilitators for plants. A mutualistic relationship had begun which was to change the appearance of the earth. Although much of the pollen was consumed by the insects, this was still a vast improvement for the plants compared to scattering their pollen to the wind.

To start with, insects had to seek out the unimpressive brown or green flowers amongst the surrounding foliage. It was now to the advantage of plants to advertise the location of their flowers, so that they could be more quickly found and to attract insects away from their competitors. So began the longest marketing campaign in history, with the early water lilies and magnolias the first plants to evolve petals, conspicuously white against the forests of green. The first pollinators may have been beetles, which many water lilies still rely on to this day. With this new reliable means of pollination, insect-pollinated plants became enormously successful and diversified. Different plants now began vying with one another for insect attention, evolving bright colours, patterns and elaborate shapes, and the land became clothed in flowers. In this battle to attract pollinators, some flowers evolved an additional weapon &ndash they began producing sugar-rich nectar as an extra reward. As these plants proliferated, so the opportunities for insects to specialise grew, and butterflies and some flies evolved long, tubular mouthparts with which to suck up nectar. The most specialised and successful group to emerge were the bees, the masters of gathering nectar and pollen to this day.

All bees feed more or less exclusively on nectar and pollen throughout their lives. While many other insects such as butterflies and hoverflies feed on flowers as adults, very few do so as young too. Flowers are sparsely distributed in the environment, and immature insects cannot fly from one to another as only adult insects have wings. The innovation unique to bees is that the adult females gather the food for their offspring, so that their larvae do not need to move at all. The larval stage is maggot-like, legless and generally rather feeble, being defenceless and capable of only very limited movement. They are entirely dependent on the food provided by the adult bees.

The first bees evolved from wasps, which were and remain predators today. The word &lsquowasp&rsquo conjures up an image of the yellow-and-black insects that often build large nests in lofts and garden sheds and which can be exceedingly annoying in late summer when their booming populations and declining food supplies force them into houses and on to our picnic tables. Actually, there are enormous numbers of wasp species, most of whom are nothing like this. A great many are parasitoids, with a gruesome lifestyle from which the sci-fi film Alien surely took its inspiration. The female of these wasps lays her eggs inside other insects, injecting them through a sharply pointed egg-laying tube. Once hatched, the grubs consume their hosts from the inside out, eventually bursting out of the dying bodies to form their pupae. Other wasp species catch prey and feed them to their grubs in small nests, and it is from one such wasp family, the Sphecidae, that bees evolved. In the Sphecidae the female wasps stock a nest, usually an underground burrow, with the corpses, or the paralysed but still living bodies, of their preferred prey. They attack a broad range of insects and spiders, with different wasp species preferring aphids, grasshoppers or beetles. At some point a species of sphecid wasp experimented with stocking its nest with pollen instead of dead insects. This could have been a gradual process, with the wasp initially adding just a little pollen to the nest provisions. As pollen is rich in protein, it would have provided a good nutritional supplement, particularly at times when prey was scarce. When the wasp eventually evolved to feed its offspring purely on pollen, it had become the first bee.

Exactly how long ago this happened we do not know for insects rarely form fossils, and so we have to piece together their history from parse information. Occasionally, insects become trapped in tree resin which fossilises to amber, beautifully preserving them for eternity. Crawling insects such as ants seem to have become trapped most often, but it seems that bees were rarely so foolish and examples of bee fossils are particularly few. The oldest known bee in amber is about 80 million years old, and is of a type known as a stingless bee, similar to species that live today in South America. These are advanced social bees that live in vast colonies, so it is a pretty good guess that the earliest bees were on the wing long before this.

A rather different source of information on the evolution of insects is provided by analysis of DNA sequences, which allow us to make educated guesses as to how long ago different evolutionary lineages diverged. Studies of the similarity of the DNA in wasps and bees suggest that the first bees appeared about 130 million years ago, 50 million years before the first known fossil bee, and probably very shortly after the first flowers evolved in the Cretaceous.

Over the millennia, bees have adapted to feeding on flowers in various ways. Many species have become hairy, which helps them to brush pollen from flowers, and also to hold it in flight. In the leafcutter bees, for instance, the pollen is stored among dense hairs on the underside of the abdomen, so that the bees often appear to have bright yellow bellies. In bumblebees and honeybees, stiff bristles on the hind legs form a basket into which pollen is placed. If one is going to visit flowers for their pollen it makes sense to also collect their nectar, for this is a great source of sugar to sustain flight. Nectar is expensive for plants to produce, and therefore many flowers evolved over time to hide their nectar, ensuring that only the insects most likely to provide them with a reliable pollen delivery service can reach it. Many bees evolved longer and longer tongues to make it easier for them to reach nectar hidden within flowers some now have tongues longer than their bodies.*

The earliest bees, 130 million years ago, were almost certainly solitary species, and the majority of present-day bee species remain so. Each female builds her own nest, usually in a small hole in the ground, or in a tree or wall. In the leafcutter bees, the nest is lined with neatly snipped semicircles of leaves, glued together with silk. Once the nest is complete, the female bee fills it with pollen mixed with nectar and lays one or more eggs. The life cycles are very variable, but usually the female does not care further for her offspring, simply sealing up the nest entrance and leaving them to eat their pollen and develop on their own. Most solitary bees in temperate climates have just one generation a year, so the offspring will sometimes spend eleven months developing in the nest before emerging as adults.

Solitary bee species tend to be small, dark or drably coloured, which is why people seldom notice them. Nonetheless many are quite common and often live in gardens, some even nesting in the old mortar between the bricks of our houses. Only rarely do the lives of these inconspicuous creatures impinge noticeably on our own, although they probably contribute substantially to pollination of many crops without us being aware of it (honeybees often get all the credit).

I was once involved in a rather strange and less welcome instance of a solitary bee impacting on humans. I received a call from aeronautical engineers who were investigating the cause of an instrument failure which had forced a military helicopter belonging to a certain well-known superpower &ndash confidentiality agreements prevent me from revealing which one &ndash to perform an emergency landing. A small but vital instrument, which measures airspeed and controls the speed of rotation of the rear rotor had failed, and the British manufacturers of the instrument found themselves under suspicion of supplying dangerously defective components. Upon close examination, it transpired that the cause of the fault was a plug of a sticky yellow substance blocking a tiny but necessary hole in the instrument casing. Their investigations suggested that the substance might be pollen, which was when I was brought in. It was indeed pollen, identifiable as belonging to some species of legume, no doubt placed there by a small solitary bee which had adopted the hole as its nest while the aircraft was parked. When it returned from a foraging trip, the bee was presumably rather disappointed to find that its nest had vanished.

Let us return to our journey through time. To recap, bees first appeared perhaps 130 million years ago, and by 80 million years ago some had evolved a social lifestyle, for the earliest fossil is of a social stingless bee. Some 65 million years after the first bees appeared (and, coincidentally, 65 million years before the present), the earth went through a catastrophic change. Most scientists these days agree that a meteor struck the earth roughly where the Yucatan Peninsula now lies, causing tidal waves and massive volcanic eruptions which filled the air with so much dust that it blocked out the sunlight, in turn causing temperatures to fall below freezing for months or years on end. Almost all large forms of life on earth then died out very swiftly, the dinosaurs among them. Amazingly, representatives of many of the smaller groups of organisms survived somehow. So far as the sparse fossil record reveals, the main insect groups &ndash bees, ants, grasshoppers, beetles and so on &ndash seem to have recovered swiftly, although it is likely that countless individual insect species became extinct. The flowering plants also survived, presumably as dormant seeds. Our own ancestors &ndash small, furry and warm-blooded &ndash may have kept themselves alive by feeding on the corpses of larger animals or on stores of seeds and nuts, and perhaps by keeping warm in the vast drifts of rotting vegetation that resulted from the forests&rsquo death. Before long the earth was once again teeming with life, albeit with rather smaller forms.

Our mammalian ancestors took advantage of the many unoccupied niches and diversified. Were it not for the meteor, it is doubtful if most of the larger mammals &ndash including ourselves &ndash would ever have appeared. Some species grew much larger, filling the roles once occupied by dinosaurs these included ground sloths that stood 6 metres tall and weighed 3 tonnes, and the vast rhinoceros-like Uintatherium. It was into this world of giants that the first bumblebees appeared, about 30 to 40 million years ago. This corresponded with a period of cooler temperatures, which may have encouraged bees to become larger and furrier. Our best guess is that the first bumblebee lived somewhere in the mountains of central Asia, since this is still the area of greatest bumblebee diversity. From here they spread west, east and north from the Himalayas to occupy Europe, China and Siberia, and even up into the Arctic Circle. As bumblebees overheat in warm climates, they did not spread far southwards towards the equator, which is why until some recent deliberate introductions there were no bumblebees in Australia, New Zealand or Africa south of the Sahara. About 20 million years ago bumblebees crossed from Siberia to North America, where they thrived and spread southwards. Eventually about 4 million years ago a handful of species moved down through the mountain chains of Central America to occupy South America, becoming the only naturally occurring bumblebees in the southern hemisphere.

So now we arrive at the present day. The world is blessed with an extraordinary diversity of species of organism. About 1.4 million have been named so far, but estimates as to the true total vary hugely from 2 million to 100 million. Two hundred and fifty of the known species are bumblebees (members of the genus Bombus, of which twenty seven occur naturally in the UK). There may be a few more yet to be found in remote regions, but probably not many. There are about 25,000 known species of bee (superfamily Apoidea, with 253 known from the UK), but many more undoubtedly remain to be discovered, particularly in the tropical regions. Bees in turn belong to the immensely successful insect order the Hymenoptera, which also includes ants and the wasps from which bees evolved, of which there are 115,000 known species. The Hymenoptera in turn are just one of many types of insect, collectively the most successful group of organisms on earth, with about 1 million named species, or about 70 per cent of all known species on earth.

Until recently, this number of species was the highest it had ever been since life began. However, in the last few thousand years it has started to drop rapidly as man has remoulded the surface of the planet. As our ancestors spread out from Africa, many of the large mammals such as mammoths, giant sloths and sabretoothed tigers swiftly disappeared, either hunted to extinction by man or driven to extinction because their prey disappeared. Most would have had no defence against groups of men hunting with spears and bows and arrows. At present, species are going extinct at somewhere between 100 and 1,000 times the natural rate, largely driven by habitat destruction and the ravages wrought by invasive species. It is estimated that one species goes extinct every twenty minutes.

So far, only three bumblebees are thought to have gone extinct globally: Bombus rubriventris, Bombus melanopoda and Bombus franklini, but surely more will follow. It is the threat of extinction of large mammals such as tigers or rhinoceros that tends to capture the public&rsquos attention, but arguably it is the loss of the smaller creatures that should give us most concern. Insects are responsible for delivering numerous &lsquoecosystem services&rsquo such as pollination and decomposition, and there is no doubt that little life on earth (including ourselves) could survive without them. As the famous biologist E. O. Wilson said, &lsquoIf all mankind were to disappear, the world would regenerate back to the rich state of equilibrium that existed ten thousand years ago. If insects were to vanish, the environment would collapse into chaos.&rsquo


* The record holder is not a bee, but a hawkmoth, Xanthopan morganii, which has a tongue of about 30 centimetres long (the moth itself being 6 centimetres long). This moth feeds upon the Madagascar star orchid Angraecum sesquipedale, in which nectar is hidden at the base of spurs 30 centimetres deep, in a beautiful example of co-evolution. Upon being sent examples of the orchid in 1862, Charles Darwin predicted that there must exist a moth with a tongue long enough to feed upon it, but it was not until 1903 that the moth was finally discovered.


What are reasons we know insects evolved on land rather than water - Biology

The first thing to notice on this evogram is that hippos are the closest living relatives of whales, but they are not the ancestors of whales. In fact, none of the individual animals on the evogram is the direct ancestor of any other, as far as we know. That's why each of them gets its own branch on the family tree.

Hippos are large and aquatic, like whales, but the two groups evolved those features separately from each other. We know this because the ancient relatives of hippos called anthracotheres (not shown here) were not large or aquatic. Nor were the ancient relatives of whales that you see pictured on this tree — such as Pakicetus. Hippos likely evolved from a group of anthracotheres about 15 million years ago, the first whales evolved over 50 million years ago, and the ancestor of both these groups was terrestrial.

These first whales, such as Pakicetus, were typical land animals. They had long skulls and large carnivorous teeth. From the outside, they don't look much like whales at all. However, their skulls — particularly in the ear region, which is surrounded by a bony wall — strongly resemble those of living whales and are unlike those of any other mammal. Often, seemingly minor features provide critical evidence to link animals that are highly specialized for their lifestyles (such as whales) with their less extreme-looking relatives.

Compared to other early whales, like Indohyus and Pakicetus, Ambulocetus looks like it lived a more aquatic lifestyle. Its legs are shorter, and its hands and feet are enlarged like paddles. Its tail is longer and more muscular, too. The hypothesis that Ambulocetus lived an aquatic life is also supported by evidence from stratigraphy — Ambulocetus's fossils were recovered from sediments that probably comprised an ancient estuary — and from the isotopes of oxygen in its bones. Animals are what they eat and drink, and saltwater and freshwater have different ratios of oxygen isotopes. This means that we can learn about what sort of water an animal drank by studying the isotopes that were incorporated into its bones and teeth as it grew. The isotopes show that Ambulocetus likely drank both saltwater and freshwater, which fits perfectly with the idea that these animals lived in estuaries or bays between freshwater and the open ocean.

Whales that evolved after Ambulocetus (Kutchicetus, etc.) show even higher levels of saltwater oxygen isotopes, indicating that they lived in nearshore marine habitats and were able to drink saltwater as today's whales can. These animals evolved nostrils positioned further and further back along the snout. This trend has continued into living whales, which have a "blowhole" (nostrils) located on top of the head above the eyes.

These more aquatic whales showed other changes that also suggest they are closely related to today's whales. For example, the pelvis had evolved to be much reduced in size and separate from the backbone. This may reflect the increased use of the whole vertebral column, including the back and tail, in locomotion. If you watch films of dolphins and other whales swimming, you'll notice that their tailfins aren't vertical like those of fishes, but horizontal. To swim, they move their tails up and down, rather than back and forth as fishes do. This is because whales evolved from walking land mammals whose backbones did not naturally bend side to side, but up and down. You can easily see this if you watch a dog running. Its vertebral column undulates up and down in waves as it moves forward. Whales do the same thing as they swim, showing their ancient terrestrial heritage.

As whales began to swim by undulating the whole body, other changes in the skeleton allowed their limbs to be used more for steering than for paddling. Because the sequence of these whales' tail vertebrae matches those of living dolphins and whales, it suggests that early whales, like Dorudon and Basilosaurus, did have tailfins. Such skeletal changes that accommodate an aquatic lifestyle are especially pronounced in basilosaurids, such as Dorudon. These ancient whales evolved over 40 million years ago. Their elbow joints were able to lock, allowing the forelimb to serve as a better control surface and resist the oncoming flow of water as the animal propelled itself forward. The hindlimbs of these animals were almost nonexistent. They were so tiny that many scientists think they served no effective function and may have even been internal to the body wall. Occasionally, we discover a living whale with the vestiges of tiny hindlimbs inside its body wall.

This vestigial hindlimb is evidence of basilosaurids' terrestrial heritage. The picture below on the left shows the central ankle bones (called astragali) of three artiodactyls, and you can see they have double pulley joints and hooked processes pointing up toward the leg-bones. Below on the right is a photo of the hind foot of a basilosaurid. You can see that it has a complete ankle and several toe bones, even though it can't walk. The basilosaurid astragalus still has a pulley and a hooked knob pointing up towards the leg bones as in artiodactyls, while other bones in the ankle and foot are fused. From the ear bones to the ankle bones, whales belong with the hippos and other artiodactyls.


Evolution’s Exemplars

The early dominance of the inner ears may explain how a young individual flatfish learns to stay grounded, but there’s still the question of why ancient flatfish flopped over in the first place. Did a mutation cause one of their eyes to wander, throwing off their balance and forcing them to swim askance? Or did one eye begin migrating to accommodate a new lifestyle at the bottom of the sea? Friedman and Schreiber think that the flatfish’s anatomical makeover followed a change in its behavior. When threatened, some modern fish are known to lie flat on their side on the seafloor and briefly bury themselves in the sand. Others tip over to play possum, only to leap up and snatch unsuspecting prey. Perhaps the flatfish’s predecessor was a bilateral open water fish particularly adept at this kind of stealth. And perhaps it was so successful that it made rock bottom its permanent home.

Jennifer Specker, a flatfish expert at the University of Rhode Island who has worked with Schreiber in the past, agrees with this line of reasoning. “One of the guesses we make is that there was not a lot of competition for early lie-and-wait predators on the bottom of the ocean,” she says. “It seems that habitat was a vacuum, and nature abhors a vacuum, so flatfish adapted to it.”

On this spotted turbot, you can see its sideways mouth and upright fin.

Spending so much time in that lowly position would inevitably have damaged one eye—not to mention wasting its visual powers. So ancient flatfish with eyes even a little closer together would have had a better chance of avoiding their predators’ bellies while still filling their own. Modern adult flatfish are both excellent camouflagers and insatiable predators, waiting patiently for the chance to pounce on their prey by flipping themselves up with their concealed pectoral fin and a jet of water expelled from their gills. From their new perch, the flatfish’s constantly swiveling eyes provide 360 degree vision.

On top of the unabashed asymmetry of an individual flatfish, there’s a whole extra level of lopsidedness among the entire population of flatfishes in the ocean. Different life stages inhabit very different regions of the ocean ecosystem. Just as metamorphosis has proved an enormously successful strategy for insects—separating larvae and adults so they do not compete for resources (think: nectar-slurping butterflies vs. leaf-munching caterpillars)—flatfish larvae have clung to the vestiges of symmetry in order to distance themselves from their parents. The young ‘uns need to swim upright to catch plankton near the surface of the ocean. Were they to remain at the seafloor where they hatched, they would surely be vacuumed up by a roving sideways pair of lips—perhaps even by their own parents.

Flatfish larvae require light to swim upright, so when the lights go off, they swim erratically.

Flatfish may be genuine anatomical anomalies—rebuffing nature’s devotion to symmetry—but they did not somehow evade natural selection, nor are they a counter-argument to Darwin. Quite the contrary. Flatfish are exemplars of evolution at work.

There are no deliberate designs in nature.

Evolution is capable of producing a wonderfully streamlined, symmetrical bottom-feeding fish: we know them as skates and rays. Stingrays and the like have pancake thin bodies oriented in a way that makes sense to us—bellies and mouths on their undersides, eyes and snout on top. But evolution did not engineer them that way on purpose. There are no deliberate designs in nature—only tenacious tinkering, marvels of serendipity, and perseverance despite frequent mishaps. When an organism’s circumstances change and demand a completely different body, evolution cannot go back to the drawing board. Instead, it works with what it has. If survival requires turning a symmetrical creature into a mish mash that looks like it was sewed together by Dr. Frankenstein, so be it. It’s weird, but it works.

And that is what biologists love about the fish—their functional freakiness. “I’ve always been drawn to really weird things different from what other people like,” Schreiber says. “If everyone is studying fruit flies and zebrafish, I’ll be damned if I am going to study them. Flatfish are just so cool. If you were to imagine what kind of fish Picasso would paint, it would be the flatfish.”


1.1 The Science of Biology

By the end of this section, you will be able to do the following:

  • Identify the shared characteristics of the natural sciences
  • Summarize the steps of the scientific method
  • Compare inductive reasoning with deductive reasoning
  • Describe the goals of basic science and applied science

What is biology? In simple terms, biology is the study of life. This is a very broad definition because the scope of biology is vast. Biologists may study anything from the microscopic or submicroscopic view of a cell to ecosystems and the whole living planet (Figure 1.2). Listening to the daily news, you will quickly realize how many aspects of biology we discuss every day. For example, recent news topics include Escherichia coli (Figure 1.3) outbreaks in spinach and Salmonella contamination in peanut butter. Other subjects include efforts toward finding a cure for AIDS, Alzheimer’s disease, and cancer. On a global scale, many researchers are committed to finding ways to protect the planet, solve environmental issues, and reduce the effects of climate change. All of these diverse endeavors are related to different facets of the discipline of biology.

The Process of Science

Biology is a science, but what exactly is science? What does the study of biology share with other scientific disciplines? We can define science (from the Latin scientia, meaning “knowledge”) as knowledge that covers general truths or the operation of general laws, especially when acquired and tested by the scientific method. It becomes clear from this definition that applying scientific method plays a major role in science. The scientific method is a method of research with defined steps that include experiments and careful observation.

We will examine scientific method steps in detail later, but one of the most important aspects of this method is the testing of hypotheses by means of repeatable experiments. A hypothesis is a suggested explanation for an event, which one can test. Although using the scientific method is inherent to science, it is inadequate in determining what science is. This is because it is relatively easy to apply the scientific method to disciplines such as physics and chemistry, but when it comes to disciplines like archaeology, psychology, and geology, the scientific method becomes less applicable as repeating experiments becomes more difficult.

These areas of study are still sciences, however. Consider archaeology—even though one cannot perform repeatable experiments, hypotheses may still be supported. For instance, an archaeologist can hypothesize that an ancient culture existed based on finding a piece of pottery. He or she could make further hypotheses about various characteristics of this culture, which could be correct or false through continued support or contradictions from other findings. A hypothesis may become a verified theory. A theory is a tested and confirmed explanation for observations or phenomena. Therefore, we may be better off to define science as fields of study that attempt to comprehend the nature of the universe.

Natural Sciences

What would you expect to see in a museum of natural sciences? Frogs? Plants? Dinosaur skeletons? Exhibits about how the brain functions? A planetarium? Gems and minerals? Maybe all of the above? Science includes such diverse fields as astronomy, biology, computer sciences, geology, logic, physics, chemistry, and mathematics (Figure 1.4). However, scientists consider those fields of science related to the physical world and its phenomena and processes natural sciences . Thus, a museum of natural sciences might contain any of the items listed above.

There is no complete agreement when it comes to defining what the natural sciences include, however. For some experts, the natural sciences are astronomy, biology, chemistry, earth science, and physics. Other scholars choose to divide natural sciences into life sciences , which study living things and include biology, and physical sciences , which study nonliving matter and include astronomy, geology, physics, and chemistry. Some disciplines such as biophysics and biochemistry build on both life and physical sciences and are interdisciplinary. Some refer to natural sciences as “hard science” because they rely on the use of quantitative data. Social sciences that study society and human behavior are more likely to use qualitative assessments to drive investigations and findings.

Not surprisingly, the natural science of biology has many branches or subdisciplines. Cell biologists study cell structure and function, while biologists who study anatomy investigate the structure of an entire organism. Those biologists studying physiology, however, focus on the internal functioning of an organism. Some areas of biology focus on only particular types of living things. For example, botanists explore plants, while zoologists specialize in animals.

Scientific Reasoning

One thing is common to all forms of science: an ultimate goal “to know.” Curiosity and inquiry are the driving forces for the development of science. Scientists seek to understand the world and the way it operates. To do this, they use two methods of logical thinking: inductive reasoning and deductive reasoning.

Inductive reasoning is a form of logical thinking that uses related observations to arrive at a general conclusion. This type of reasoning is common in descriptive science. A life scientist such as a biologist makes observations and records them. These data can be qualitative or quantitative, and one can supplement the raw data with drawings, pictures, photos, or videos. From many observations, the scientist can infer conclusions (inductions) based on evidence. Inductive reasoning involves formulating generalizations inferred from careful observation and analyzing a large amount of data. Brain studies provide an example. In this type of research, scientists observe many live brains while people are engaged in a specific activity, such as viewing images of food. The scientist then predicts the part of the brain that “lights up” during this activity to be the part controlling the response to the selected stimulus, in this case, images of food. Excess absorption of radioactive sugar derivatives by active areas of the brain causes the various areas to "light up". Scientists use a scanner to observe the resultant increase in radioactivity. Then, researchers can stimulate that part of the brain to see if similar responses result.

Deductive reasoning or deduction is the type of logic used in hypothesis-based science. In deductive reasoning, the pattern of thinking moves in the opposite direction as compared to inductive reasoning. Deductive reasoning is a form of logical thinking that uses a general principle or law to predict specific results. From those general principles, a scientist can deduce and predict the specific results that would be valid as long as the general principles are valid. Studies in climate change can illustrate this type of reasoning. For example, scientists may predict that if the climate becomes warmer in a particular region, then the distribution of plants and animals should change.

Both types of logical thinking are related to the two main pathways of scientific study: descriptive science and hypothesis-based science. Descriptive (or discovery) science , which is usually inductive, aims to observe, explore, and discover, while hypothesis-based science , which is usually deductive, begins with a specific question or problem and a potential answer or solution that one can test. The boundary between these two forms of study is often blurred, and most scientific endeavors combine both approaches. The fuzzy boundary becomes apparent when thinking about how easily observation can lead to specific questions. For example, a gentleman in the 1940s observed that the burr seeds that stuck to his clothes and his dog’s fur had a tiny hook structure. On closer inspection, he discovered that the burrs’ gripping device was more reliable than a zipper. He eventually experimented to find the best material that acted similarly, and produced the hook-and-loop fastener popularly known today as Velcro. Descriptive science and hypothesis-based science are in continuous dialogue.

The Scientific Method

Biologists study the living world by posing questions about it and seeking science-based responses. Known as scientific method, this approach is common to other sciences as well. The scientific method was used even in ancient times, but England’s Sir Francis Bacon (1561–1626) first documented it (Figure 1.5). He set up inductive methods for scientific inquiry. The scientific method is not used only by biologists researchers from almost all fields of study can apply it as a logical, rational problem-solving method.

The scientific process typically starts with an observation (often a problem to solve) that leads to a question. Let’s think about a simple problem that starts with an observation and apply the scientific method to solve the problem. One Monday morning, a student arrives at class and quickly discovers that the classroom is too warm. That is an observation that also describes a problem: the classroom is too warm. The student then asks a question: “Why is the classroom so warm?”

Proposing a Hypothesis

Recall that a hypothesis is a suggested explanation that one can test. To solve a problem, one can propose several hypotheses. For example, one hypothesis might be, “The classroom is warm because no one turned on the air conditioning.” However, there could be other responses to the question, and therefore one may propose other hypotheses. A second hypothesis might be, “The classroom is warm because there is a power failure, and so the air conditioning doesn’t work.”

Once one has selected a hypothesis, the student can make a prediction. A prediction is similar to a hypothesis but it typically has the format “If . . . then . . . .” For example, the prediction for the first hypothesis might be, “If the student turns on the air conditioning, then the classroom will no longer be too warm.”

Testing a Hypothesis

A valid hypothesis must be testable. It should also be falsifiable , meaning that experimental results can disprove it. Importantly, science does not claim to “prove” anything because scientific understandings are always subject to modification with further information. This step—openness to disproving ideas—is what distinguishes sciences from non-sciences. The presence of the supernatural, for instance, is neither testable nor falsifiable. To test a hypothesis, a researcher will conduct one or more experiments designed to eliminate one or more of the hypotheses. Each experiment will have one or more variables and one or more controls. A variable is any part of the experiment that can vary or change during the experiment. The control group contains every feature of the experimental group except it is not given the manipulation that the researcher hypothesizes. Therefore, if the experimental group's results differ from the control group, the difference must be due to the hypothesized manipulation, rather than some outside factor. Look for the variables and controls in the examples that follow. To test the first hypothesis, the student would find out if the air conditioning is on. If the air conditioning is turned on but does not work, there should be another reason, and the student should reject this hypothesis. To test the second hypothesis, the student could check if the lights in the classroom are functional. If so, there is no power failure and the student should reject this hypothesis. The students should test each hypothesis by carrying out appropriate experiments. Be aware that rejecting one hypothesis does not determine whether or not one can accept the other hypotheses. It simply eliminates one hypothesis that is not valid (Figure 1.6). Using the scientific method, the student rejects the hypotheses that are inconsistent with experimental data.

While this “warm classroom” example is based on observational results, other hypotheses and experiments might have clearer controls. For instance, a student might attend class on Monday and realize she had difficulty concentrating on the lecture. One observation to explain this occurrence might be, “When I eat breakfast before class, I am better able to pay attention.” The student could then design an experiment with a control to test this hypothesis.

In hypothesis-based science, researchers predict specific results from a general premise. We call this type of reasoning deductive reasoning: deduction proceeds from the general to the particular. However, the reverse of the process is also possible: sometimes, scientists reach a general conclusion from a number of specific observations. We call this type of reasoning inductive reasoning, and it proceeds from the particular to the general. Researchers often use inductive and deductive reasoning in tandem to advance scientific knowledge (Figure 1.7). In recent years a new approach of testing hypotheses has developed as a result of an exponential growth of data deposited in various databases. Using computer algorithms and statistical analyses of data in databases, a new field of so-called "data research" (also referred to as "in silico" research) provides new methods of data analyses and their interpretation. This will increase the demand for specialists in both biology and computer science, a promising career opportunity.

Visual Connection

In the example below, the scientific method is used to solve an everyday problem. Match the scientific method steps (numbered items) with the process of solving the everyday problem (lettered items). Based on the results of the experiment, is the hypothesis correct? If it is incorrect, propose some alternative hypotheses.

1. Observation a. There is something wrong with the electrical outlet.
2. Question b. If something is wrong with the outlet, my coffeemaker also won’t work when plugged into it.
3. Hypothesis (answer) c. My toaster doesn’t toast my bread.
4. Prediction d. I plug my coffee maker into the outlet.
5. Experiment e. My coffeemaker works.
6. Result f. Why doesn’t my toaster work?

Visual Connection

Decide if each of the following is an example of inductive or deductive reasoning.

  1. All flying birds and insects have wings. Birds and insects flap their wings as they move through the air. Therefore, wings enable flight.
  2. Insects generally survive mild winters better than harsh ones. Therefore, insect pests will become more problematic if global temperatures increase.
  3. Chromosomes, the carriers of DNA, are distributed evenly between the daughter cells during cell division. Therefore, each daughter cell will have the same chromosome set as the mother cell.
  4. Animals as diverse as humans, insects, and wolves all exhibit social behavior. Therefore, social behavior must have an evolutionary advantage.

The scientific method may seem too rigid and structured. It is important to keep in mind that, although scientists often follow this sequence, there is flexibility. Sometimes an experiment leads to conclusions that favor a change in approach. Often, an experiment brings entirely new scientific questions to the puzzle. Many times, science does not operate in a linear fashion. Instead, scientists continually draw inferences and make generalizations, finding patterns as their research proceeds. Scientific reasoning is more complex than the scientific method alone suggests. Notice, too, that we can apply the scientific method to solving problems that aren’t necessarily scientific in nature.

Two Types of Science: Basic Science and Applied Science

The scientific community has been debating for the last few decades about the value of different types of science. Is it valuable to pursue science for the sake of simply gaining knowledge, or does scientific knowledge only have worth if we can apply it to solving a specific problem or to bettering our lives? This question focuses on the differences between two types of science: basic science and applied science.

Basic science or “pure” science seeks to expand knowledge regardless of the short-term application of that knowledge. It is not focused on developing a product or a service of immediate public or commercial value. The immediate goal of basic science is knowledge for knowledge’s sake, although this does not mean that, in the end, it may not result in a practical application.

In contrast, applied science or “technology,” aims to use science to solve real-world problems, making it possible, for example, to improve a crop yield, find a cure for a particular disease, or save animals threatened by a natural disaster (Figure 1.8). In applied science, the problem is usually defined for the researcher.

Some individuals may perceive applied science as “useful” and basic science as “useless.” A question these people might pose to a scientist advocating knowledge acquisition would be, “What for?” However, a careful look at the history of science reveals that basic knowledge has resulted in many remarkable applications of great value. Many scientists think that a basic understanding of science is necessary before researchers develop an application, therefore, applied science relies on the results that researchers generate through basic science. Other scientists think that it is time to move on from basic science in order to find solutions to actual problems. Both approaches are valid. It is true that there are problems that demand immediate attention however, scientists would find few solutions without the help of the wide knowledge foundation that basic science generates.

One example of how basic and applied science can work together to solve practical problems occurred after the discovery of DNA structure led to an understanding of the molecular mechanisms governing DNA replication. DNA strands, unique in every human, are in our cells, where they provide the instructions necessary for life. When DNA replicates, it produces new copies of itself, shortly before a cell divides. Understanding DNA replication mechanisms enabled scientists to develop laboratory techniques that researchers now use to identify genetic diseases, pinpoint individuals who were at a crime scene, and determine paternity. Without basic science, it is unlikely that applied science could exist.

Another example of the link between basic and applied research is the Human Genome Project, a study in which researchers analyzed and mapped each human chromosome to determine the precise sequence of DNA subunits and each gene's exact location. (The gene is the basic unit of heredity represented by a specific DNA segment that codes for a functional molecule. An individual’s complete collection of genes is his or her genome.) Researchers have studied other less complex organisms as part of this project in order to gain a better understanding of human chromosomes. The Human Genome Project (Figure 1.9) relied on basic research with simple organisms and, later, with the human genome. An important end goal eventually became using the data for applied research, seeking cures and early diagnoses for genetically related diseases.

While scientists usually carefully plan research efforts in both basic science and applied science, note that some discoveries are made by serendipity , that is, by means of a fortunate accident or a lucky surprise. Scottish biologist Alexander Fleming discovered penicillin when he accidentally left a petri dish of Staphylococcus bacteria open. An unwanted mold grew on the dish, killing the bacteria. Fleming's curiosity to investigate the reason behind the bacterial death, followed by his experiments, led to the discovery of the antibiotic penicillin, which is produced by the fungus Penicillium. Even in the highly organized world of science, luck—when combined with an observant, curious mind—can lead to unexpected breakthroughs.

Reporting Scientific Work

Whether scientific research is basic science or applied science, scientists must share their findings in order for other researchers to expand and build upon their discoveries. Collaboration with other scientists—when planning, conducting, and analyzing results—is important for scientific research. For this reason, important aspects of a scientist’s work are communicating with peers and disseminating results to peers. Scientists can share results by presenting them at a scientific meeting or conference, but this approach can reach only the select few who are present. Instead, most scientists present their results in peer-reviewed manuscripts that are published in scientific journals. Peer-reviewed manuscripts are scientific papers that a scientist’s colleagues or peers review. These colleagues are qualified individuals, often experts in the same research area, who judge whether or not the scientist’s work is suitable for publication. The process of peer review helps to ensure that the research in a scientific paper or grant proposal is original, significant, logical, and thorough. Grant proposals, which are requests for research funding, are also subject to peer review. Scientists publish their work so other scientists can reproduce their experiments under similar or different conditions to expand on the findings.

A scientific paper is very different from creative writing. Although creativity is required to design experiments, there are fixed guidelines when it comes to presenting scientific results. First, scientific writing must be brief, concise, and accurate. A scientific paper needs to be succinct but detailed enough to allow peers to reproduce the experiments.

The scientific paper consists of several specific sections—introduction, materials and methods, results, and discussion. This structure is sometimes called the “IMRaD” format. There are usually acknowledgment and reference sections as well as an abstract (a concise summary) at the beginning of the paper. There might be additional sections depending on the type of paper and the journal where it will be published. For example, some review papers require an outline.

The introduction starts with brief, but broad, background information about what is known in the field. A good introduction also gives the rationale of the work. It justifies the work carried out and also briefly mentions the end of the paper, where the researcher will present the hypothesis or research question driving the research. The introduction refers to the published scientific work of others and therefore requires citations following the style of the journal. Using the work or ideas of others without proper citation is plagiarism .

The materials and methods section includes a complete and accurate description of the substances the researchers use, and the method and techniques they use to gather data. The description should be thorough enough to allow another researcher to repeat the experiment and obtain similar results, but it does not have to be verbose. This section will also include information on how the researchers made measurements and the types of calculations and statistical analyses they used to examine raw data. Although the materials and methods section gives an accurate description of the experiments, it does not discuss them.

Some journals require a results section followed by a discussion section, but it is more common to combine both. If the journal does not allow combining both sections, the results section simply narrates the findings without any further interpretation. The researchers present results with tables or graphs, but they do not present duplicate information. In the discussion section, the researchers will interpret the results, describe how variables may be related, and attempt to explain the observations. It is indispensable to conduct an extensive literature search to put the results in the context of previously published scientific research. Therefore, researchers include proper citations in this section as well.

Finally, the conclusion section summarizes the importance of the experimental findings. While the scientific paper almost certainly answers one or more scientific questions that the researchers stated, any good research should lead to more questions. Therefore, a well-done scientific paper allows the researchers and others to continue and expand on the findings.

Review articles do not follow the IMRAD format because they do not present original scientific findings, or primary literature. Instead, they summarize and comment on findings that were published as primary literature and typically include extensive reference sections.


Paleozoic Era: Facts & Information

The Paleozoic Era, which ran from about 542 million years ago to 251 million years ago, was a time of great change on Earth. The era began with the breakup of one supercontinent and the formation of another. Plants became widespread. And the first vertebrate animals colonized land.

Life in the Paleozoic

The Paleozoic began with the Cambrian Period, 53 million years best known for ushering in an explosion of life on Earth. This "Cambrian explosion" included the evolution of arthropods (ancestors of today's insects and crustaceans) and chordates (animals with rudimentary spinal cords).

In the Paleozoic Era, life flourished in the seas. After the Cambrian Period came the 45-million-year Ordovician Period, which is marked in the fossil record by an abundance of marine invertebrates. Perhaps the most famous of these invertebrates was the trilobite, an armored arthropod that scuttled around the seafloor for about 270 million years before going extinct.

After the Ordovician Period came the Silurian Period (443 million years ago to 416 million years ago), which saw the spread of jawless fish throughout the seas. Mollusks and corals also thrived in the oceans, but the big news was what was happening on land: the first undisputed evidence of terrestrial life.

This was the time when plants evolved, though they most likely did not yet have leaves or the vascular tissue that allows modern plants to siphon up water and nutrients. Those developments would appear in the Devonian Period, the next geological period of the Paleozoic. Ferns appeared, as did the first trees. At the same time, the first vertebrates were colonizing the land. These vertebrates were called tetrapods, and they were widely diverse: Their appearance ranged from lizardlike to snakelike, and their size ranged from 4 inches (10 cm) long to 16 feet (5 meters) long, according to a study released in 2009 in the Journal of Anatomy.

As the tetrapods took over, they had company: The Devonian Period saw the rise of the first land-living arthropods, including the earliest ancestors of spiders.

Paleozoic evolution

Life continued its march in the late Paleozoic. The Carboniferous Period, which lasted from about 359 million years ago to 299 million years ago, answered the question, "Which came first &mdash the chicken or the egg?" definitively. Long before birds evolved, tetrapods began laying eggs on land for the first time during this period, allowing them to break away from an amphibious lifestyle.

Trilobites were fading as fish became more diverse. The ancestors of conifers appeared, and dragonflies ruled the skies. Tetrapods were becoming more specialized, and two new groups of animals evolved. The first were marine reptiles, including lizards and snakes. The second were the archosaurs, which would give rise to crocodiles, dinosaurs and birds. Most creepily, this era is sometimes referred to as the "Age of the Cockroaches," because roaches' ancient ancestor (Archimylacris eggintoni) was found all across the globe during the Carboniferous.

The last period of the Paleozoic was the Permian Period, which began 299 million years ago and wrapped up 251 million years ago. This period would end with the largest mass extinction ever: the Permian extinction.

Before the Permian mass extinction, though, the warm seas teemed with life. Coral reefs flourished, providing shelter for fish and shelled creatures, such as nautiloids and ammonoids. Modern conifers and ginkgo trees evolved on land. Terrestrial vertebrates evolved to become herbivores, taking advantage of the new plant life that had colonized the land.

Paleozoic geology and climate

All this evolution took place against the backdrop of shifting continents and a changing climate. During the Cambrian Period of the Paleozoic, the continents underwent a change. They had been joined as one supercontinent, Rodinia, but during the Cambrian Period, Rodinia fragmented into Gondwana (consisting of what would eventually become the modern continents of the Southern Hemisphere) and smaller continents made up of bits and pieces of the land that would eventually make up today's northern continents.

The Cambrian was warm worldwide, but would be followed by an ice age in the Ordovician, which caused glaciers to form, sending sea levels downward. Gondwana moved further south during the Ordovician, while the smaller continents started to move closer together. In the Silurian Period, the land masses that would become North America, central and northern Europe, and western Europe moved even closer together. Sea levels rose again, creating shallow inland seas.

In the Devonian, the northern land masses continued merging, and they finally joined together into the supercontinent Euramerica. Gondwana still existed, but the rest of the planet was ocean. By the last period of the Paleozoic, the Permian, Euramerica and Gondwana became one, forming perhaps the most famous supercontinent of them all: Pangaea. The giant ocean surrounding Pangaea was called Panthalassa. Pangaea's interior was likely very dry, because its massive size prevented water-bearing rain clouds from penetrating far beyond the coasts.


All Species Evolved From Single Cell, Study Finds

Creationism called "absolutely horrible hypothesis"—statistically speaking.

All life on Earth evolved from a single-celled organism that lived roughly 3.5 billion years ago, a new study seems to confirm.

The study supports the widely held "universal common ancestor" theory first proposed by Charles Darwin more than 150 years ago.

Using computer models and statistical methods, biochemist Douglas Theobald calculated the odds that all species from the three main groups, or "domains," of life evolved from a common ancestor—versus, say, descending from several different life-forms or arising in their present form, Adam and Eve style.

The domains are bacteria, bacteria-like microbes called Archaea, and eukaryotes, the group that includes plants and other multicellular species, such as humans.

The "best competing multiple ancestry hypothesis" has one species giving rise to bacteria and one giving rise to Archaea and eukaryotes, said Theobald, a biochemist at Brandeis University in Waltham, Massachusetts.

But, based on the new analysis, the odds of that are "just astronomically enormous," he said. "The number's so big, it's kind of silly to say it"—1 in 10 to the 2,680th power, or 1 followed by 2,680 zeros.

Theobald also tested the creationist idea that humans arose in their current form and have no evolutionary ancestors.

The statistical analysis showed that the independent origin of humans is "an absolutely horrible hypothesis," Theobald said, adding that the probability that humans were created separately from everything else is 1 in 10 to the 6,000th power.

(As of publication time, requests for interviews with several creationist scientists had been either declined or unanswered.)

Putting Darwin to the Test

All species in all three domains share 23 universal proteins, though the proteins' DNA sequences—instructions written in the As, Cs, Gs, and Ts of DNA bases—differ slightly among the three domains (quick genetics overview).

The 23 universal proteins perform fundamental cellular activities, such as DNA replication and the translation of DNA into proteins, and are crucial to the survival of all known life-forms—from the smallest microbes to blue whales.

A universal common ancestor is generally assumed to be the reason the 23 proteins are as similar as they are, Theobald said.

That's because, if the original protein set was the same for all creatures, a relatively small number of mutations would have been needed to arrive at the modern proteins, he said. If life arose from multiple species—each with a different set of proteins—many more mutations would have been required.

But Theobald hoped to go beyond conventional wisdom.

"What I wanted to do was not make the assumption that similar traits imply a shared ancestry . because we know that's not always true," Theobald said.

"For instance, you could get similarities that are not due to common ancestry but that are due to natural selection"—that is, when environmental forces, such as predators or climate, result in certain mutations taking hold, such as claws or thicker fur.

Biologists call the independent development of similar traits in different lineages "convergent evolution." The wings of bats, birds, and insects are prime examples: They perform similar functions but evolved independently of one another.

But it's highly unlikely that the protein groups would have independently evolved into such similar DNA sequences, according to the new study, to be published tomorrow in the journal Nature.

"I asked, What's the probability that I would see a human DNA polymerase [protein] sequence and another protein with an E. coli DNA polymerase sequence?" he explained.

"It turns out that probability is much higher if you use the hypothesis that [humans and E. coli] are actually related."

No Special Treatment for Evolutionary Theory?

David Penny, an evolutionary biologist at Massey University in New Zealand, called the grand scope of Theobald's study "bold."

Penny had been part of a similar, but more narrowly focused, study in the 1980s. His team had looked at shared proteins in mammals and concluded that different mammalian species are likely descended from a common ancestor.

Testing the theory of universal common ancestry is important, because biologists should question their major tenets just as scientists in other fields do, said Penny, who wasn't part of the new study.

"Evolution," he said, "should not be given any special status."

Editor's note: Two corrections have been made to this article. In the first sentence "million" has been changed to "billion." In the seventh paragraph, "10 followed by 2,680 zeros" has been changed to "1 followed by 2,680 zeros." Many thanks to readers for pointing out these typos.


Physiological Systems in Insects

As the largest living group on earth, insects can provide us with insight into adaptation, evolution, and survival. The 2nd edition of this standard text for insect physiology courses and entomologists provides the most comprehensive analysis of the systems that make insects important contributors to our environment. Physiological Systems in Insects discusses the role of insect molecular biology, nueroendocrinology, biochemistry, and genetics in our understanding of insects. Organized according to insect physiological functions, this book is fully updated with the latest and foundational research that has influenced understanding of the patterns and processes of insects.

As the largest living group on earth, insects can provide us with insight into adaptation, evolution, and survival. The 2nd edition of this standard text for insect physiology courses and entomologists provides the most comprehensive analysis of the systems that make insects important contributors to our environment. Physiological Systems in Insects discusses the role of insect molecular biology, nueroendocrinology, biochemistry, and genetics in our understanding of insects. Organized according to insect physiological functions, this book is fully updated with the latest and foundational research that has influenced understanding of the patterns and processes of insects.


1 Nakedness

We are the only smooth-skinned primates. Nakedness is an advantage underwater because it allows the body to glide gracefully through the water with ease. Why, then, do we still have hair on our heads?

It is hypothesized that cranial hair remained to protect us from sun radiation. Hair shields the head, but the shoulders and upper arms also tend to have more hair. The hair that did stick around is arranged diagonally, pointing inward toward the midline of the body. This pattern provides the least resistance while swimming.

There&rsquos a close connection between nakedness and water. Mammals that have lost their body hair are the aquatic ones like the hippo, dolphin, manatee. and more. The elephant may be pointed to as an example of a nonaquatic animal that lost its hair, but hold on. Turns out, they have an aquatic ancestor as well. In fact, all naked pachyderms do, even the rhino.

It seems that every naked mammal was conditioned by water at some point. [10] Why not us?


Watch the video: Top 10 Γιγαντιαία Και Πιο Ανατριχιαστικά Εντομα Που Δε Θα Χεις Δει Ποτέ Σου (December 2021).