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What does it mean for a species to be ancient?

What does it mean for a species to be ancient?


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When we say that a species like cockroaches is ancient, what does it mean exactly? Does that mean that cockroaches haven't evolved for a long time? But isn't evolution always occurring? So is that because they haven't evolved as much and are very similar to their ancestors, ie they had a "very slow rate of evolution"?


It depends on the context.

first "cockroaches are ancient" is different than a species being ancient, cockroaches are not a species but a group of species with a similar morphology and ancestry (similar to a clade).

  1. It can mean they are mrophologically similar to their ancestors. Which is very different than saying they have not evolved. It means the pressures on the linage have not favored much in the way of morphological change. Some shapes just work well,(or reach equilibrium) and once you reach it the morphology don't change much even when other things are changing.

  2. It often means that the split between the lineage in question and other groups is old. example, you could say mammals are ancient for instance because the mammal lineage split off the rest of the amniotes 275 millions years ago. They have changed a great deal since then but the groups as a whole goes back a long time. the issue here is these splits are minor when they occurred, like any other specialization event, but look big due to human constructed categories.

  3. But it can also mean that the lineage has not undergone a specification event for a long time, It has changed but has not left behind any offshoots, this is the rarest case but can happen.

Note however this is a phrase the media like to throw around when it doesn't have a solid scientific definition, it is a qualitative contextual statement. They often have little understanding of its meanings. They also often fail to clarify which they mean, and often fail to properly define the "thing" being ancient.


Eusocial species

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Eusocial species, any colonial animal species that lives in multigenerational family groups in which the vast majority of individuals cooperate to aid relatively few (or even a single) reproductive group members. Eusocial species often exhibit extreme task specialization, which makes colonies potentially very efficient in gathering resources. Workers in eusocial colonies are thought to forgo reproduction due to constraints on independent breeding. Such constraints include shortages of food, territories, protection, skill, nest sites, appropriate weather for breeding, and available mates. Workers may never reproduce during their entire lives however, they gain exclusive fitness benefits by aiding the reproduction of a queen, who is typically their mother. Such assistance often takes the form of foraging for food, caring for the young, and maintaining and protecting the nest.

Eusocial behaviour is found in ants and bees (order Hymenoptera), some wasps in the family Vespidae, termites (order Isoptera sometimes placed in the cockroach order, Blattodea), some thrips (order Thysanoptera), aphids (family Aphididae), and possibly some species of beetles (order Coleoptera). Blesmols, such as the naked mole rat (Heterocephalus glaber) and the Damaraland mole rat (Cryptomys damarensis), are the only vertebrates that engage in truly eusocial behaviour.

This article was most recently revised and updated by John P. Rafferty, Editor.


What Does It Mean to Be a Species? Genetics Is Changing the Answer

For Charles Darwin, "species" was an undefinable term, "one arbitrarily given for the sake of convenience to a set of individuals closely resembling each other." That hasn't stopped scientists in the 150 years since then from trying, however. When scientists today sit down to study a new form of life, they apply any number of more than 70 definitions of what constitutes a species—and each helps get at a different aspect of what makes organisms distinct.

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In a way, this plethora of definitions helps prove Darwin’s point: The idea of a species is ultimately a human construct. With advancing DNA technology, scientists are now able to draw finer and finer lines between what they consider species by looking at the genetic code that defines them. How scientists choose to draw that line depends on whether their subject is an animal or plant the tools available and the scientist’s own preference and expertise.

Now, as new species are discovered and old ones thrown out, researchers want to know: How do we define a species today? Let’s look back at the evolution of the concept and how far it’s come.

Perhaps the most classic definition is a group of organisms that can breed with each other to produce fertile offspring, an idea originally set forth in 1942 by evolutionary biologist Ernst Mayr. While elegant in its simplicity, this concept has since come under fire by biologists, who argue that it didn't apply to many organisms, such as single-celled ones that reproduce asexually, or those that have been shown to breed with other distinct organisms to create hybrids.

Alternatives arose quickly. Some biologists championed an ecological definition that assigned species according to the environmental niches they fill (this animal recycles soil nutrients, this predator keeps insects in check). Others asserted that a species was a set of organisms with physical characteristics that were distinct from others (the peacock's fanned tail, the beaks of Darwin's finches).

The discovery of DNA's double helix prompted the creation of yet another definition, one in which scientists could look for minute genetic differences and draw even finer lines denoting species. Based on a 1980 book by biologists Niles Eldredge and Joel Cracraft, under the definition of a phylogenetic species, animal species now can differ by just 2 percent of their DNA to be considered separate. 

"Back in 1996, the world recognized half the number of species of lemur there are today," says Craig Hilton-Taylor, who manages the International Union for the Conservation of Nature's Red List of threatened species. (Today there are more than 100 recognized lemur species.) Advances in genetic technology have given the organization a much more detailed picture of the world's species and their health.

These advances have also renewed debates about what it means to be a species, as ecologists and conservationists discover that many species that once appeared singular are actually multitudes. Smithsonian entomologist John Burns has used DNA technology to distinguish a number of so-called "cryptic species"—organisms that appear physically identical to a members of a certain species, but have significantly different genomes. In a� study, he was able to determine that a species of tropical butterfly identified in 1775 actually encompassed 10 separate species.

In 2010, advanced DNA technology allowed scientists to solve an age-old debate over African elephants. By sequencing the rarer and more complex DNA from the nuclei of elephant cells, instead of the more commonly used mitochondrial DNA, they determined that African elephants actually comprised two separate species that diverged millions of years ago.

"You can no more call African elephants the same species as you can Asian elephants and the mammoth," David Reich, a population geneticist and lead author on the study, told Nature News.

Smithsonian entomology curator W. Donald Duckworth studies a tray of moth specimens in 1975. Taxonomists have traditionally relied on physical characteristics to tease apart species. (Kjell Bloch Sandved / Smithsonian Archives)

In the wake of these and other paradigm-shifting discoveries, Mayr’s original concept is rapidly falling apart. Those two species of African elephants, for instance, kept interbreeding as recently as 500,000 years ago. Another example falls closer to home: Recent analyses of DNA remnants in the genes of modern humans have found that humans and Neanderthals—usually thought of as separate species that diverged roughly 700,000 years ago—interbred as recently as 100,000 years ago.

So are these elephants and hominids still separate species?

This isn't just an argument of scientific semantics. Pinpointing an organism's species is critical for any efforts to protect that animal, especially when it comes to government action. A species that gets listed on the U.S. Endangered Species Act, for example, gains protection from any destructive actions from the government and private citizens.These protections would be impossible to enforce without the ability to determine which organisms are part of that endangered species.

At the same time, advances in sequencing techniques and technology are helping today’s scientists better piece together exactly which species are being impacted by which human actions.

"We're capable of recognizing almost any species [now]," says Mary Curtis, a wildlife forensic scientist who leads the genetics team at the U.S. Fish and Wildlife Service's Forensics Laboratory. Her lab is responsible for identifying any animal remains or products that are suspected to have been illegally traded or harvested. Since adopting DNA sequencing techniques more than 20 years ago, the lab has been able to make identifications much more rapidly, and increase the number of species it can reliably recognize by the hundreds.

"A lot of the stuff we get in in genetics has no shape or form," Curtis says. The lab receives slabs of unidentified meat, crafted decorative items or even the stomach contents of other animals. Identifying these unusual items is usually out of the reach of taxonomic experts using body shape, hair identification and other physical characteristics. "We can only do that with DNA," Curtis says.

Still, Curtis, who previously studied fishes, doesn't discount the importance of traditional taxonomists. "A lot of the time we're working together," she says. Experienced taxonomists can often quickly identify recognizable cases, leaving the more expensive DNA sequencing for the situations that really need it.

Not all ecologists are sold on these advances. Some express concerns about "taxonomic inflation," as the number of species identified or reclassified continues to skyrocket. They worry that as scientists draw lines based on the narrow shades of difference that DNA technology enables them to see, the entire concept of a species is being diluted.

"Not everything you can distinguish should be its own species," as German zoologist Andreas Wilting told the Washington Post in 2015. Wilting had proposed condensing tigers into just two subspecies, from the current nine.

Other scientists are concerned about the effects that reclassifying once-distinct species can have on conservation efforts. In 1973, the endangered dusky seaside sparrow, a small bird once found in Florida, missed out on potentially helpful conservation assistance by being reclassified as a subspecies of the much more populous seaside sparrow . Less than two decades later, the dusky seaside sparrow was extinct.

Hilton-Taylor isn’t sure yet when or how the ecological and conservation communities will settle on the idea of a species. But he does expect that DNA technology will have a significant impact on disrupting and reshaping the work of those fields. “Lots of things are changing,” Hilton-Taylor says. “That's the world we're living in.”

This uncertainty is in many ways reflective of the definition of species today too, Hilton-Taylor says. The IUCN draws on the expertise of various different groups and scientists to compile data for its Red List, and some of those groups have embraced broader or narrower concepts of what makes a species, with differing reliance on DNA. “There's such a diversity of scientists out there,” Hilton-Taylor says. “We just have to go with what we have.”


What Does It Mean to Be a Dominant Species? (with pictures)

In an ecological community, the species which is most numerous and forms the bulk of biomass may be considered the dominant species. Ecological dominance may also be defined as the species that has the most influence on other species in the same environment. Dominant species include plants and animals that influence the ecological conditions of an environment by their size, abundance, or behavior and determine which other animals or plants can survive in that environment. In some environments, there may be one or more dominant species.

Good examples of ecological domination in the plant world are the forest communities of the Rocky Mountains. After a forest fire, plants and trees progress through various stages, with small plants like grasses and ferns growing back first. Eventually, small trees like aspen and birch take root and sprout upward cutting off sunlight from those smaller ground plants on the forest floor. After a number of years, coniferous trees like pines and spruces will grow above the smaller trees. At each stage of growth, one species of plant succeeds the previous species and, for a time, exists as the dominant species in the forest ecosystem.

In the animal kingdom, the top predator may become the dominant. A good example is the Yellowstone Lake ecosystem in Wyoming, where predatory lake trout were illegally introduced in 1994. Prior to the introduction of the piscivorous, or fish eating, lake trout, the Yellowstone cutthroat trout was the dominant species in the lake ecosystem. In 2011, if not controlled, lake trout could reduce the Yellowstone cutthroat trout population by as much as 90% over the next 20 years and might eliminate them completely. The lake trout would then be considered the dominant fish in this ecological community.

The top predator might not always be the top species, though. Sometimes a species attains dominance through sheer numbers, and in this case, the total biomass of a species makes it the dominant one. Large numbers of a single species can exert tremendous influence on an ecosystem. One simple example of this would be a locust infestation in a wheat field. With an abundant food supply and no predators, a population of locusts can increase its numbers over a very short period of time, becoming the dominant species in this ecosystem.


A species considered to be facing a very high risk of extinction in the wild.

A species considered to be facing a high risk of extinction in the wild.

Amphibians:

Conifers:

Reef Corals:

Sharks and Rays:

Selected Crustaceans:

Mammals:

Birds:

The IUCN Red List also re-assesses how species are doing over time. If things have improved for a given species&mdashmeaning the population has grown due to conservation efforts&mdashthen that species will be &lsquodownlisted&rsquo to a less critical status. For example, the giant panda was downlisted from &lsquoendangered&rsquo to the lesser status of &lsquovulnerable&rsquo in 2016 thanks to dedicated work to protect them. The flip side of this is &lsquouplisted,&rsquo an indication that a species population is dropping.

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WWF works to save at-risk wildlife from around the globe. We&rsquore protecting and connecting the habitat of endangered tigers stopping poaching of the critically endangered black rhino and fighting back against the illegal trade of ivory from vulnerable African elephants.

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Biological Evidence

Biogeography

The geographic distribution of organisms on the planet follows patterns that are best explained by evolution in conjunction with the movement of tectonic plates over geological time. Broad groups that evolved before the breakup of the supercontinent Pangaea (about 200 million years ago) are distributed worldwide. Groups that evolved since the breakup appear uniquely in regions of the planet, such as the unique flora and fauna of northern continents that formed from the supercontinent Laurasia and of the southern continents that formed from the supercontinent Gondwana. The presence of members of the plant family Proteaceae in Australia, southern Africa, and South America is best explained by their appearance prior to the southern supercontinent Gondwana breaking up.

The great diversification of marsupials in Australia and the absence of other mammals reflect Australia&rsquos long isolation. Australia has an abundance of endemic species&mdashspecies found nowhere else&mdashwhich is typical of islands whose isolation by expanses of water prevents species migration. This geographical isolation makes islands &ldquohotbeds&rdquo for selective pressures. Due to these pressures, over time these species diverge evolutionarily into new species that look very different from their ancestors that may exist on the mainland. The marsupials of Australia, the finches on the Galápagos, and many species on the Hawaiian Islands are all unique to their one point of origin, yet they display distant relationships to ancestral species on mainlands.

Molecular Biology

Like anatomical structures, the structures of the molecules of life reflect descent with modification. Evidence of a common ancestor for all of life is reflected in the universality of DNA as the genetic material and in the near universality of the genetic code and the machinery of DNA replication and expression. Fundamental divisions in life between the three domains are reflected in major structural differences in otherwise conservative structures such as the components of ribosomes and the structures of membranes. In general, the relatedness of groups of organisms is reflected in the similarity of their DNA sequences&mdashexactly the pattern that would be expected from descent and diversification from a common ancestor.

DNA sequences have also shed light on some of the mechanisms of evolution. For example, it is clear that the evolution of new functions for proteins commonly occurs after gene duplication events that allow the free modification of one copy by mutation, selection, or drift (changes in a population&rsquos gene pool resulting from chance), while the other copy continues to produce a functional protein.

Biogeography offers further clues about evolutionary relationships. The presence of related organisms across continents indicates when these organisms may have evolved. For example, some flora and fauna of the northern continents are similar across these landmasses but distinct from that of the southern continents. Islands such as Australia and the Galapagos chain often have unique species that evolved after these landmasses separated from the mainland. Finally, molecular biology provides data supporting the theory of evolution. In particular, the universality of DNA and near universality of the genetic code for proteins shows that all life once shared a common ancestor. DNA also provides clues into how evolution may have happened. Gene duplications allow one copy to undergo mutational events without harming an organism, as one copy continues to produce functional protein.


Section Summary

To build phylogenetic trees, scientists must collect character information that allows them to make evolutionary connections between organisms. Using morphologic and molecular data, scientists work to identify homologous characteristics and genes. Similarities between organisms can stem either from shared evolutionary history (homologies) or from separate evolutionary paths (analogies). After homologous information is identified, scientists use cladistics to organize these events as a means to determine an evolutionary timeline. Scientists apply the concept of maximum parsimony, which states that the likeliest order of events is probably the simplest shortest path. For evolutionary events, this would be the path with the least number of major divergences that correlate with the evidence.

Figure 12.2.3 Which animals in this figure belong to a clade that includes animals with hair? Which evolved first: hair or the amniotic egg?

Rabbits and humans belong in the clade that includes animals with hair. The amniotic egg evolved before hair, because the Amniota clade branches off earlier than the clade that encompasses animals with hair.


Endemic Species

An endemic species is a species which is restricted geographically to a particular area. Endemism in a species can arise through a species going extinct in other regions. This is called paleoendemism. Alternatively, new species are always endemic to the region in which they first appear. This is called neoendemism. Both forms of endemism are discussed in more detail under the heading “Types of Endemism”, below.

Endemic species, regardless of how they came to be restricted to a particular area, experience the same threats to their existence. The smaller the region, the more dire the threat toward the survival of the species. Any action that reduces the size of the land, or divides it in any way can significantly affect the normal patterns of the endemic species. While endemism and being endangered or threatened are different things, being endemic to a small area is often a warning sign that a species may become threatened or endangered.

This is not always the case, as many globally distributed species are also considered threatened or endangered. In recent years, many sharks have joined the list. While they are distributed throughout many of the ocean’s waters, the harvesting of shark fins for soup has decimated their populations globally. Endemism sometimes protects species from being exploited globally, simply because of the fact that the species only exists in a small area. This can even make the species easier to protect, because the land can be placed under a conservation easement to restrict the construction and human impact on the land.


Natural Selection

Darwin and Descent with Modification

Figure 1. Darwin observed that beak shape varies among finch species. He postulated that the beak of an ancestral species had adapted over time to equip the finches to acquire different food sources.

Charles Darwin is best known for his discovery of natural selection. In the mid-nineteenth century, the actual mechanism for evolution was independently conceived of and described by two naturalists: Charles Darwin and Alfred Russel Wallace. Importantly, each naturalist spent time exploring the natural world on expeditions to the tropics. From 1831 to 1836, Darwin traveled around the world on H.M.S. Beagle, including stops in South America, Australia, and the southern tip of Africa. Wallace traveled to Brazil to collect insects in the Amazon rainforest from 1848 to 1852 and to the Malay Archipelago from 1854 to 1862. Darwin’s journey, like Wallace’s later journeys to the Malay Archipelago, included stops at several island chains, the last being the Galápagos Islands west of Ecuador. On these islands, Darwin observed species of organisms on different islands that were clearly similar, yet had distinct differences. For example, the ground finches inhabiting the Galápagos Islands comprised several species with a unique beak shape (Figure 1).

The species on the islands had a graded series of beak sizes and shapes with very small differences between the most similar. He observed that these finches closely resembled another finch species on the mainland of South America. Darwin imagined that the island species might be species modified from one of the original mainland species. Upon further study, he realized that the varied beaks of each finch helped the birds acquire a specific type of food. For example, seed-eating finches had stronger, thicker beaks for breaking seeds, and insect-eating finches had spear-like beaks for stabbing their prey.

Wallace and Darwin both observed similar patterns in other organisms and they independently developed the same explanation for how and why such changes could take place. Darwin called this mechanism natural selection. Natural selection, also known as “survival of the fittest,” is the more prolific reproduction of individuals with favorable traits that survive environmental change because of those traits this leads to evolutionary change.

For example, a population of giant tortoises found in the Galapagos Archipelago was observed by Darwin to have longer necks than those that lived on other islands with dry lowlands. These tortoises were “selected” because they could reach more leaves and access more food than those with short necks. In times of drought when fewer leaves would be available, those that could reach more leaves had a better chance to eat and survive than those that couldn’t reach the food source. Consequently, long-necked tortoises would be more likely to be reproductively successful and pass the long-necked trait to their offspring. Over time, only long-necked tortoises would be present in the population.

Natural selection, Darwin argued, was an inevitable outcome of three principles that operated in nature. First, most characteristics of organisms are inherited, or passed from parent to offspring. Although no one, including Darwin and Wallace, knew how this happened at the time, it was a common understanding. Second, more offspring are produced than are able to survive, so resources for survival and reproduction are limited. The capacity for reproduction in all organisms outstrips the availability of resources to support their numbers. Thus, there is competition for those resources in each generation. Both Darwin and Wallace’s understanding of this principle came from reading an essay by the economist Thomas Malthus who discussed this principle in relation to human populations. Third, offspring vary among each other in regard to their characteristics and those variations are inherited. Darwin and Wallace reasoned that offspring with inherited characteristics which allow them to best compete for limited resources will survive and have more offspring than those individuals with variations that are less able to compete. Because characteristics are inherited, these traits will be better represented in the next generation. This will lead to change in populations over generations in a process that Darwin called descent with modification. Ultimately, natural selection leads to greater adaptation of the population to its local environment it is the only mechanism known for adaptive evolution.

Papers by Darwin and Wallace (Figure 2) presenting the idea of natural selection were read together in 1858 before the Linnean Society in London. The following year Darwin’s book, On the Origin of Species, was published. His book outlined in considerable detail his arguments for gradual changes and adaptive survival by natural selection.

Figure 2. Both (a) Charles Darwin and (b) Alfred Wallace wrote scientific papers on natural selection that were presented together before the Linnean Society in 1858.

Demonstrations of evolution by natural selection are time consuming and difficult to obtain. One of the best examples has been demonstrated in the very birds that helped to inspire Darwin’s theory: the Galápagos finches. Peter and Rosemary Grant and their colleagues have studied Galápagos finch populations every year since 1976 and have provided important demonstrations of natural selection. The Grants found changes from one generation to the next in the distribution of beak shapes with the medium ground finch on the Galápagos island of Daphne Major. The birds have inherited variation in the bill shape with some birds having wide deep bills and others having thinner bills. During a period in which rainfall was higher than normal because of an El Niño, the large hard seeds that large-billed birds ate were reduced in number however, there was an abundance of the small soft seeds which the small-billed birds ate. Therefore, survival and reproduction were much better in the following years for the small-billed birds. In the years following this El Niño, the Grants measured beak sizes in the population and found that the average bill size was smaller. Since bill size is an inherited trait, parents with smaller bills had more offspring and the size of bills had evolved to be smaller. As conditions improved in 1987 and larger seeds became more available, the trend toward smaller average bill size ceased.


Summary

Evolution is the process of adaptation through mutation which allows more desirable characteristics to be passed to the next generation. Over time, organisms evolve more characteristics that are beneficial to their survival. For living organisms to adapt and change to environmental pressures, genetic variation must be present. With genetic variation, individuals have differences in form and function that allow some to survive certain conditions better than others. These organisms pass their favorable traits to their offspring. Eventually, environments change, and what was once a desirable, advantageous trait may become an undesirable trait and organisms may further evolve. Evolution may be convergent with similar traits evolving in multiple species or divergent with diverse traits evolving in multiple species that came from a common ancestor. Evidence of evolution can be observed by means of DNA code and the fossil record, and also by the existence of homologous and vestigial structures.