heterotroph hypothesis def

The Heterotroph Hypothesis and High School Biology

Cite this chapter.

• Claude A. Welch 3  

440 Accesses

Theory is finally coming of age in biology. It was to the physical sciences that philosophers invariably turned when they discussed the role of theory as a source of fruitful and generative ideas leading to new experiments and revolutionary concepts. But the biologists have broken loose from their routine role of description and classification. They are caught up in the exciting interaction of facts and ideas and this relatively new affection “has changed their complexion”--to paraphrase an old song. Broad explanatory theories and conceptual schemes have finally crept into biology, but it has been only slightly more than a century that the three major concepts--cell theory, evolution theory, and gene theory--have attained operational respectability. This “operational respectability” however, has not come easily in respect to evolution theory, particularly in the American secondary schools. Evolution, especially Darwinian natural-selection, is still a bete noire in a sizable portion of American high schools. But the corner has been turned, and new directions for high school biology are in process.

This is a preview of subscription content, log in via an institution to check access.

Access this chapter

• Available as PDF
• Read on any device
• Instant download
• Own it forever
• Compact, lightweight edition
• Dispatched in 3 to 5 business days
• Free shipping worldwide - see info

Tax calculation will be finalised at checkout

Purchases are for personal use only

Institutional subscriptions

Unable to display preview.  Download preview PDF.

Author information

Authors and affiliations.

Department of Biology, Macalester College, Saint Paul, Minnesota, 55101, USA

Claude A. Welch

You can also search for this author in PubMed   Google Scholar

Editor information

Editors and affiliations.

Department of Biology, University of South Carolina, Columbia, South Carolina, USA

Duane L. Rohlfing

A. N. Bakh Institute of Biochemistry, Academy of Sciences of the USSR, Moscow, USSR

A. I. Oparin

Rights and permissions

Reprints and permissions

Copyright information

© 1972 Plenum Press

About this chapter

Welch, C.A. (1972). The Heterotroph Hypothesis and High School Biology. In: Rohlfing, D.L., Oparin, A.I. (eds) Molecular Evolution. Springer, Boston, MA. https://doi.org/10.1007/978-1-4684-2019-7_34

Download citation

DOI : https://doi.org/10.1007/978-1-4684-2019-7_34

Publisher Name : Springer, Boston, MA

Print ISBN : 978-1-4684-2021-0

Online ISBN : 978-1-4684-2019-7

eBook Packages : Springer Book Archive

Share this chapter

Anyone you share the following link with will be able to read this content:

Sorry, a shareable link is not currently available for this article.

Provided by the Springer Nature SharedIt content-sharing initiative

• Publish with us

Policies and ethics

• Find a journal
• Track your research

Lesson: Chapter - 8

Origin of life: the heterotroph hypothesis.

Life on Earth began about 3.5 billion years ago. At that point in the development of the Earth, the atmosphere was very different from what it is today. As opposed to the current atmosphere, which is mostly nitrogen and oxygen, the early Earth atmosphere contained mostly hydrogen, water, ammonia, and methane.

In experiments, scientists have showed that the electrical discharges of lightning, radioactivity, and ultraviolet light caused the elements in the early Earth atmosphere to form the basic molecules of biological chemistry, such as nucleotides, simple proteins, and ATP. It seems likely, then, that the Earth was covered in a hot, thin soup of water and organic materials. Over time, the molecules became more complex and began to collaborate to run metabolic processes. Eventually, the first cells came into being. These cells were  heterotrophs , which could not produce their own food and instead fed on the organic material from the primordial soup. (These heterotrophs give this theory its name.)

Video Lesson - Heterotroph Hypothesis

The anaerobic metabolic processes of the heterotrophs released carbon dioxide into the atmosphere, which allowed for the evolution of photosynthetic autotrophs, which could use light and CO2 to produce their own food. The autotrophs released oxygen into the atmosphere. For most of the original anaerobic heterotrophs, oxygen proved poisonous. The few heterotrophs that survived the change in environment generally evolved the capacity to carry out aerobic respiration. Over the subsequent billions of years, the aerobic autotrophs and heterotrophs became the dominant life-forms on the planet and evolved into all of the diversity of life now visible on Earth.

Evidence of Evolution

Humankind has always wondered about its origins and the origins of the life around it. Many cultures have ancient creation myths that explain the origin of the Earth and its life. In Western cultures, ideas about evolution were originally based on the Bible. The book of Genesis relates how God created all life on Earth about 6,000 years ago in a mass creation event. Proponents of creationism support the Genesis account and state that species were created exactly as they are currently found in nature. This oldest formal conception of the origin of life still has proponents today.

However, about 200 years ago, scientific evidence began to cast doubt on creationism. This evidence comes in a variety of forms.

Rock and Fossil Formation

Fossils provide the only direct evidence of the history of evolution. Fossil formation occurs when sediment covers some material or fills an impression. Very gradually, heat and pressure harden the sediment and surrounding minerals replace it, creating fossils. Fossils of prehistoric life can be bones, shells, or teeth that are buried in rock, and they can also be traces of leaves or footprints left behind by organisms.

Together, fossils can be used to construct a fossil record that offers a timeline of fossils reaching back through history. To puzzle together the fossil record, scientists have to be able to date the fossils to a certain time period. The strata of rock in which fossils are found give clues about their relative ages. If two fossils are found in the same geographic location, but one is found in a layer of sediment that is beneath the other layer, it is likely that the fossil in the lower layer is from an earlier era. After all, the first layer of sediment had to already be on the ground in order for the second layer to begin to build up on top of it. In addition to sediment layers, new techniques such as radioactive decay or carbon dating can also help determine a fossil’s age.

There are, however, limitations to the information fossils can supply. First of all, fossilization is an improbable event. Most often, remains and other traces of organisms are crushed or consumed before they can be fossilized. Additionally, fossils can only form in areas with sedimentary rock, such as ocean floors. Organisms that live in these environments are therefore more likely to become fossils. Finally, erosion of exposed surfaces or geological movements such as earthquakes can destroy already formed fossils. All of these conditions lead to large and numerous gaps in the fossil record.

Comparative Anatomy

Scientists often try to determine the relatedness of two organisms by comparing external and internal structures. The study of comparative anatomy is an extension of the logical reasoning that organisms with similar structures must have acquired these traits from a common ancestor. For example, the flipper of a whale and a human arm seem to be quite different when looked at on the outside. But the bone structure of each is surprisingly similar, suggesting that whales and humans have a common ancestor way back in prehistory. Anatomical features in different species that point to a common ancestor are called homologous structures .

However, comparative anatomists cannot just assume that every similar structure points to a common evolutionary origin. A hasty and reckless comparative anatomist might assume that bats and insects share a common ancestor, since both have wings. But a closer look at the structure of the wings shows that there is very little in common between them besides their function. In fact, the bat wing is much closer in structure to the arm of a man and the fin of a whale than it is to the wings of an insect. In other words, bats and insects evolved their ability to fly along two very separate evolutionary paths. These sorts of structures, which have superficial similarities because of similarity of function but do not result from a common ancestor, are called analogous structures .

In addition to homologous and analogous structures, vestigial structures , which serve no apparent modern function, can help determine how an organism may have evolved over time. In humans the appendix is useless, but in cows and other mammalian herbivores a similar structure is used to digest cellulose. The existence of the appendix suggests that humans share a common evolutionary ancestry with other mammalian herbivores. The fact that the appendix now serves no purpose in humans demonstrates that humans and mammalian herbivores long ago diverged in their evolutionary paths.

Comparative Embryology

Homologous structures not present in adult organisms often do appear in some form during embryonic development. Species that bear little resemblance to each other in their adult forms may have strikingly similar embryonic stages. In some ways, it is almost as if the embryo passes through many evolutionary stages to produce the mature organism. For example, for a large portion of its development, the human embryo possesses a tail, much like those of our close primate relatives. This tail is usually reabsorbed before birth, but occasionally children are born with the ancestral structure intact. Even though they are not generally present in the adult organism, tails could be considered homologous traits between humans and primates.

In general, the more closely related two species are, the more their embryological processes of development resemble each other.

Molecular Evolution

Just as comparative anatomy is used to determine the anatomical relatedness of species, molecular biology can be used to determine evolutionary relationships at the molecular level. Two species that are closely related will have fewer genetic or protein differences between them than two species that are distantly related and split in evolutionary development long in the past.

Certain genes or proteins in organisms change at a constant rate over time. These genes and proteins, called molecular clocks because they are so constant in their rate of change, are especially useful in comparing the molecular evolution of different species. Scientists can use the rate of change in the gene or protein to calculate the point at which two species last shared a common ancestor. For example, ribosomal RNA has a very slow rate of change, so it is commonly used as a molecular clock to determine relationships between extremely ancient species. Cytochrome c, a protein that plays an important role in aerobic respiration, is an example of a protein commonly used as a molecular clock.

Theories of Evolution

In the nineteenth century, as increasing evidence suggested that species changed over time, scientists began to develop theories to explain how these changes arise. During this time, there were two notable theories of evolution. The first, proposed by Lamarck, turned out to be incorrect. The second, developed by Darwin, is the basis of all evolutionary theory.

Lamarck: Use and Disuse

The first notable theory of evolution was proposed by Jean-Baptiste Lamarck (1744–1829). He described a two-part mechanism by which evolutionary change was gradually introduced into the species and passed down through generations. His theory is referred to as the theory of transformation or  Lamarckism.

The classic example used to explain Lamarckism is the elongated neck of the giraffe. According to Lamarck’s theory, a given giraffe could, over a lifetime of straining to reach high branches, develop an elongated neck. This vividly illustrates Lamarck’s belief that use could amplify or enhance a trait. Similarly, he believed that disuse would cause a trait to become reduced. According to Lamarck’s theory, the wings of penguins, for example, were understandably smaller than the wings of other birds because penguins did not use their wings to fly.

The second part of Lamarck’s mechanism for evolution involved the inheritance of acquired traits . He believed that if an organism’s traits changed over the course of its lifetime, the organism would pass these traits along to its offspring.

Lamarck’s theory has been proven wrong in both of its basic premises. First, an organism cannot fundamentally change its structure through use or disuse. A giraffe’s neck will not become longer or shorter by stretching for leaves. Second, modern genetics shows that it is impossible to pass on acquired traits; the traits that an organism can pass on are determined by the genotype of its sex cells, which does not change according to changes in phenotype.

Darwin: Natural Selection

While sailing aboard the HMS Beagle, the Englishman Charles Darwin had the opportunity to study the wildlife of the Galápagos Islands. On the islands, he was amazed by the great diversity of life. Most particularly, he took interest in the islands’ various finches, whose beaks were all highly adapted to their particular lifestyles. He hypothesized that there must be some process that created such diversity and adaptation, and he spent much of his time trying to puzzle out just what the process might be. In 1859, he published his theory of natural selection and the evolution it produced. Darwin explained his theory through four basic points:

• Each species produces more offspring than can survive.
• The individual organisms that make up a larger population are born with certain variations.
• The overabundance of offspring creates a competition for survival among individual organisms. The individuals that have the most favorable variations will survive and reproduce, while those with less favorable variations are less likely to survive and reproduce.
• Variations are passed down from parent to offspring.

Natural selection creates change within a species through competition, or the struggle for life. Members of a species compete with each other and with other species for resources. In this competition, the individuals that are the most fit—the individuals that have certain variations that make them better adapted to their environments—are the most able to survive, reproduce, and pass their traits on to their offspring. The competition that Darwin’s theory describes is sometimes called the survival of the fittest.

Natural Selection in Action

One of the best examples of natural selection is a true story that took place in England around the turn of the century. Near an agricultural town lived a species of moth. The moth spent much of its time perched on the lichen-covered bark of trees of the area. Most of the moths were of a pepper color, though a few were black. When the pepper-color moths were attached to the lichen-covered bark of the trees in the region, it was quite difficult for predators to see them. The black moths were easy to spot against the black-and-white speckled trunks.

The nearby city, however, slowly became industrialized. Smokestacks and foundries in the town puffed out soot and smoke into the air. In a fairly short time, the soot settled on everything, including the trees, and killed much of the lichen. As a result, the appearance of the trees became nearly black in color. Suddenly the pepper-color moths were obvious against the dark tree trunks, while the black moths that had been easy to spot now blended in against the trees. Over the course of years, residents of the town noticed that the population of the moths changed. Whereas about 90 percent of the moths used to be light, after the trees became black, the moth population became increasingly black.

Development of New Species

The scientific definition of a species is a discrete group of organisms that can only breed within its own confines. In other words, the members of one species cannot interbreed with the members of another species. Each species is said to experience reproductive isolation. If you think about evolution in terms of genetics, this definition of species makes a great deal of sense: if species could interbreed, they could share gene flow, and their evolution would not be separate. But since species cannot interbreed, each species exists on its own individual path.

As populations change, new species evolve. This process is known as speciation . Through speciation, the earliest simple organisms were able to branch out and populate the world with millions of different species. Speciation is also called divergent evolution, since when a new species develops, it diverges from a previous form. All homologous traits are produced by divergent evolution. Whales and humans share a distant common ancestor. Through speciation, that ancestor underwent divergent evolution and gave rise to new species, which in turn gave rise to new species, which over the course of millions of years resulted in whales and humans. The original ancestor had a limb structure that, over millions of years and successive occurrences of divergent evolution, evolved into the fin of the whale and the arm of the human.

Speciation occurs when two populations become reproductively isolated. Once reproductive isolation occurs for a new species, it will begin to evolve independently. There are two main ways in which speciation might occur. Allopatric speciation occurs when populations of a species become geographically isolated so that they cannot interbreed. Over time, the populations may become genetically different in response to the unique selection pressures operating in their different environments. Eventually the genetic differences between the two populations will become so extreme that the two populations would be unable to interbreed even if the geographic barrier disappeared.

A second, more common form of speciation is adaptive radiation, which is the creation of several new species from a single parent species. Think of a population of a given species, which we’ll imaginatively name population 1. The population moves into a new habitat and establishes itself in a niche, or role, in the habitat (we discuss niches in more detail in the chapter on Ecology). In so doing, it adapts to its new environment and becomes different from the parent species. If a new population of the parent species, population 2, moves into the area, it too will try to occupy the same niche as population 1. Competition between population 1 and population 2 ensues, placing pressure on both groups to adapt to separate niches, further distinguishing them from each other and the parent species. As this happens many times in a given habitat, several new species may be formed from a single parent species in a relatively short time. The immense diversity of finches that Darwin observed on the Galápagos Islands is an excellent example of the products of adaptive radiation.

Convergent Evolution

When different species inhabit similar environments, they face similar selection pressures, or use parts of their bodies to perform similar functions. These similarities can cause the species to evolve similar traits, in a process called convergent evolution. From living in the cold, watery, arctic regions, where most of the food exists underwater, penguins and killer whales have evolved some similar characteristics: both are streamlined to help them swim more quickly underwater, both have layers of fat to keep them warm, both have similar white-and-black coloration that helps them to avoid detection, and both have developed fins (or flippers) to propel them through the water. All of these similar traits are examples of analogous traits, which are the product of convergent evolution.

Convergent evolution sounds as if it is the opposite of divergent evolution, but that isn’t actually true. Convergent evolution is only superficial. From the outside, the fin of a whale may look like the flipper of a penguin, but the bone structure of a whale fin is still more similar to the limbs of other mammals than it is to the structure of penguin flippers. More importantly, convergent evolution never results in two species gaining the ability to interbreed; convergent evolution can’t take two species and turn them into one.

Next to display next topic in the chapter.

Test Prep Lessons With Video Lessons and Explained MCQ

Large number of solved practice MCQ with explanations. Video Lessons and 10 Fully explained Grand/Full Tests.

Current Menu

Main menu (click/tap to open), quantitative, logical/reasoning, more for you, data sufficiency.

Easily crack the most logical section of the GMAT

English Grammar

easy to learn English Grammar for test preparation

Biology for Test Preparation

Prepare Biology for tests with lessons and practice mcq

You may be interested in

Colleges in cities of balochistan.

Comprehensive lists of colleges in ...

Colleges in Dera ismail khan

Find major schools in your location ...

Social Articles

A list of Articles on Social Issues ...

Precis Writing

How to write Precis with solved exa ...

Pakistan Army - PMA Long Course

Join Pakistan Army through PMA Long ...

GAT: Graduate Admission Test By NTS

GAT - General is required for gradu ...

PU University of the Punjab

The oldest university in Pakistan - ...

NUML National University of Modern Language

NUML National University of Modern ...

EntryTest.com is a test preparation service for students seeking successful career.

About Disclaimer

Quick Test Prep

NUST NET IBA Karachi SAT LUMS LCAT LSE

NTS GAT NTS NAT GMAT GRE ACT

Study Abroad

Education Abroad Business Schools MS in USA

• school Campus Bookshelves
• menu_book Bookshelves
• perm_media Learning Objects
• login Login
• how_to_reg Request Instructor Account
• hub Instructor Commons

Margin Size

• Download Page (PDF)
• Download Full Book (PDF)
• Periodic Table
• Physics Constants
• Scientific Calculator
• Reference & Cite
• Tools expand_more
• Readability

selected template will load here

This action is not available.

20.6: Heterotrophs - First vs Autotrophs-First- Some Evolutionary Considerations

• Last updated
• Save as PDF
• Page ID 89045

• Gerald Bergtrom
• University of Wisconsin-Milwaukee

\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)

\( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)

\( \newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\)

( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\)

\( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\)

\( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\)

\( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\)

\( \newcommand{\Span}{\mathrm{span}}\)

\( \newcommand{\id}{\mathrm{id}}\)

\( \newcommand{\kernel}{\mathrm{null}\,}\)

\( \newcommand{\range}{\mathrm{range}\,}\)

\( \newcommand{\RealPart}{\mathrm{Re}}\)

\( \newcommand{\ImaginaryPart}{\mathrm{Im}}\)

\( \newcommand{\Argument}{\mathrm{Arg}}\)

\( \newcommand{\norm}[1]{\| #1 \|}\)

\( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\AA}{\unicode[.8,0]{x212B}}\)

\( \newcommand{\vectorA}[1]{\vec{#1}}      % arrow\)

\( \newcommand{\vectorAt}[1]{\vec{\text{#1}}}      % arrow\)

\( \newcommand{\vectorB}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)

\( \newcommand{\vectorC}[1]{\textbf{#1}} \)

\( \newcommand{\vectorD}[1]{\overrightarrow{#1}} \)

\( \newcommand{\vectorDt}[1]{\overrightarrow{\text{#1}}} \)

\( \newcommand{\vectE}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash{\mathbf {#1}}}} \)

In the alkaline vent scenario, chemiosmotic metabolism predated life. Therefore, the first chemoautotrophic cells did not need the fermentative reactions required by cells in a heterotrophs-first origin scenario. Even though all cells alive today incorporate a form of glycolytic metabolism, glycolysis may in fact, not be the oldest known biochemical pathway , as we have thought for so long.

In support of a late evolution of glycolytic enzymes, those of the archaea show little structural resemblance to those of bacteria. If fermentative heterotrophy was a late evolutionary development, then LUCA and its early descendants would lack a well-developed glycolytic pathway. Instead, the LUCA must have been one of many ‘experimental’ autotrophic cells, most likely a chemoautotroph deriving free energy from inorganic chemicals in the environment. To account for heterotrophy in the three domains of life, it must have evolved separately in the two antecedent branches descending from the last universal common ancestor of bacterial, archaeal, and eukaryotic organisms. The evolution of similar traits (fermentative biochemical pathways in this case) in unrelated organisms is called convergent evolution .

The phylogenetic tree in Figure 20.11 below features an autotrophic LUCA in an autotrophs-first scenario. The tree traces a separate (convergent) evolution of heterotrophy in two branches of the descendants of the LUCA by tracing the spread of fermentative pathways in all living things on the familiar three domain phylogeny.

ENCYCLOPEDIC ENTRY

Heterotrophs.

A heterotroph is an organism that consumes other organisms in a food chain.

Biology, Ecology

Chameleons are a bizarre and colorful example of a heterotroph, an organism that consumes other animals or plants – like this unfortunate cricket – to sustain itself.

Photograph by kuritafsheen

A heterotroph is an organism that eats other plants or animals for energy and nutrients. The term stems from the Greek words hetero for “other” and trophe for “nourishment.”

Organisms are characterized into two broad categories based upon how they obtain their energy and nutrients: autotrophs and heterotrophs . Autotrophs are known as producers because they are able to make their own food from raw materials and energy. Examples include plants, algae , and some types of bacteria . Heterotrophs are known as consumers because they consume producers or other consumers. Dogs, birds, fish, and humans are all examples of heterotrophs .

Heterotrophs occupy the second and third levels in a food chain , a sequence of organisms that provide energy and nutrients for other organisms. Each food chain consists of three trophic levels, which describe an organism’s role in an ecosystem. Occupying the first trophic level are autotrophs , such as plants and algae . Herbivores —organisms that eat plants—occupy the second level. Carnivores (organisms that eat meat) and omnivores (organisms that eat plants and meat) occupy the third level. Both primary ( herbivores ) and secondary ( carnivores and omnivores ) consumers are heterotrophs , while primary producers are autotrophs .

A third type of heterotrophic consumer is a detritivore . These organisms obtain food by feeding on the remains of plants and animals as well as fecal matter. Detritivores play an important role in maintaining a healthy ecosystem by recycling waste. Examples of detritivores include fungi, worms, and insects.

There are two subcategories of heterotrophs : photoheterotrophs and chemoheterotrophs . Photo heterotrophs are organisms that get their energy from light, but must still consume carbon from other organisms, as they cannot utilize carbon dioxide from the air. Chemo heterotrophs , by contrast, get both their energy and carbon from other organisms.

A major difference between autotrophs and heterotrophs is that the former are able to make their own food by photosynthesis whereas the latter cannot. Photosynthesis is a process that involves making glucose (a sugar) and oxygen from water and carbon dioxide using energy from sunlight. Autotrophs are able to manufacture energy from the sun, but heterotrophs must rely on other organisms for energy.

Another major difference between autotrophs and heterotrophs is that autotrophs have an important pigment called chlorophyll , which enables them to capture the energy of sunlight during photosynthesis , whereas heterotrophs do not. Without this pigment, photosynthesis could not occur.

Heterotrophs benefit from photosynthesis in a variety of ways. They depend on the process for oxygen, which is produced as a byproduct during photosynthesis. Moreover, photosynthesis sustains the autotrophs that heterotrophs depend on to survive. While meat-eating carnivores may not directly depend on photosynthetic plants to survive, they do depend on other animals that consume photosynthetic plants as a food source.

Media Credits

The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited.

Production Managers

Program specialists, last updated.

October 19, 2023

User Permissions

For information on user permissions, please read our Terms of Service. If you have questions about how to cite anything on our website in your project or classroom presentation, please contact your teacher. They will best know the preferred format. When you reach out to them, you will need the page title, URL, and the date you accessed the resource.

If a media asset is downloadable, a download button appears in the corner of the media viewer. If no button appears, you cannot download or save the media.

Text on this page is printable and can be used according to our Terms of Service .

Interactives

Any interactives on this page can only be played while you are visiting our website. You cannot download interactives.

Related Resources

If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

To log in and use all the features of Khan Academy, please enable JavaScript in your browser.

AP®︎/College Biology

Course: ap®︎/college biology   >   unit 7.

• Earth formation
• Beginnings of life
• Origins of life

Hypotheses about the origins of life

• The RNA origin of life
• Origins of life on Earth

Key points:

• The Earth formed roughly 4.5 ‍   billion years ago, and life probably began between 3.5 ‍   and 3.9 ‍   billion years ago.
• The Oparin-Haldane hypothesis suggests that life arose gradually from inorganic molecules, with “building blocks” like amino acids forming first and then combining to make complex polymers.
• The Miller-Urey experiment provided the first evidence that organic molecules needed for life could be formed from inorganic components.
• Some scientists support the RNA world hypothesis , which suggests that the first life was self-replicating RNA. Others favor the metabolism-first hypothesis , placing metabolic networks before DNA or RNA.
• Simple organic compounds might have come to early Earth on meteorites.

Introduction

When did life appear on earth, the earliest fossil evidence of life, how might life have arisen.

• Simple inorganic molecules could have reacted (with energy from lightning or the sun) to form building blocks like amino acids and nucleotides, which could have accumulated in the oceans, making a "primordial soup." 3 ‍  
• The building blocks could have combined in further reactions, forming larger, more complex molecules (polymers) like proteins and nucleic acids, perhaps in pools at the water's edge.
• The polymers could have assembled into units or structures that were capable of sustaining and replicating themselves. Oparin thought these might have been “colonies” of proteins clustered together to carry out metabolism, while Haldane suggested that macromolecules became enclosed in membranes to make cell-like structures 4 , 5 ‍   .

From inorganic compounds to building blocks

Were miller and urey's results meaningful, from building blocks to polymers, what was the nature of the earliest life, the "genes-first" hypothesis, the "metabolism-first" hypothesis, what might early cells have looked like, another possibility: organic molecules from outer space.

• Miller, Urey, and others showed that simple inorganic molecules could combine to form the organic building blocks required for life as we know it.
• Once formed, these building blocks could have come together to form polymers such as proteins or RNA.
• Many scientists favor the RNA world hypothesis, in which RNA, not DNA, was the first genetic molecule of life on Earth. Other ideas include the pre-RNA world hypothesis and the metabolism-first hypothesis.
• Organic compounds could have been delivered to early Earth by meteorites and other celestial objects.

Works cited:

• Harwood, R. (2012). Patterns in palaeontology: The first 3 billion years of evolution. Palaeontology , 2(11), 1-22. Retrieved from http://www.palaeontologyonline.com/articles/2012/patterns-in-palaeontology-the-first-3-billion-years-of-evolution/ .
• Wacey, D., Kilburn, M. R., Saunders, M., Cliff, J., and Brasier, M. D. (2011). Microfossils of sulphur-metabolizing cells in 3.4-billion-year-old rocks of Western Australia. Nature Geoscience , 4 , 698-702. http://dx.doi.org/10.1038/ngeo1238 .
• Primordial soup. (2016, January 20). Retrieved May 22, 2016 from Wikipedia: https://en.wikipedia.org/wiki/Primordial_soup .
• Gordon-Smith, C. (2003). The Oparin-Haldane hypothesis. In Origin of life: Twentieth century landmarks . Retrieved from http://www.simsoup.info/Origin_Landmarks_Oparin_Haldane.html .
• The Oparin-Haldane hypothesis. (2015, June 14). In Structural biochemistry . Retrieved May 22, 2016 from Wikibooks: https://en.wikibooks.org/wiki/Structural_Biochemistry/The_Oparin-Haldane_Hypothesis .
• Kimball, J. W. (2015, May 17). Miller's experiment. In Kimball's biology pages . Retrieved from http://www.biology-pages.info/A/AbioticSynthesis.html#Miller's_Experiment .
• Earth’s early atmosphere. (Dec 2, 2011). In Astrobiology Magazine . Retrieved from http://www.astrobio.net/topic/solar-system/earth/geology/earths-early-atmosphere/ .
• McCollom, T. M. (2013). Miller-Urey and beyond: What have learned about prebiotic organic synthesis reactions in the past 60 years? Annual Review of Earth and Planetary Sciences , 41_, 207-229. http://dx.doi.org/10.1146/annurev-earth-040610-133457 .
• Powner, M. W., Gerland, B., and Sutherland, J. D. (2009). Synthesis of activated pyrimidine ribonucleotides in prebiotically plausible conditions. Nature , 459 , 239-242. http://dx.doi.org/10.1038/nature08013 .
• Lurquin, P. F. (June 5, 2003). Proteins and metabolism first: The iron-sulfur world. In The origins of life and the universe (pp. 110-111). New York, NY: Columbia University Press.
• Ferris, J. P. (2006). Montmorillonite-catalysed formation of RNA oligomers: The possible role of catalysis in the origins of life. Philos. Trans. R. Soc. Lond. B. Bio.l Sci ., 361 (1474), 1777–1786. http://dx.doi.org/10.1098/rstb.2006.1903 .
• Kimball, J. W. (2015, May 17). Assembling polymers. In Kimball's biology pages . Retrieved from
• Montmorillonite. (2016, 28 March). Retrieved May 22, 2016 from Wikipedia: https://en.wikipedia.org/wiki/Montmorillonite .
• Wilkin, D. and Akre, B. (2016, March 23). First organic molecules - Advanced. In CK-12 biology advanced concepts . Retrieved from http://www.ck12.org/book/CK-12-Biology-Advanced-Concepts/section/10.8/ .
• Hollenstein, M. (2015). DNA catalysis: The chemical repertoire of DNAzymes. Molecules , 20 (11), 20777–20804. http://dx.doi.org/10.3390/molecules201119730 .
• Breaker, R. R. and Joyce, G. F. (2014). The expanding view of RNA and DNA function. Chemistry & biology , 21 (9), 1059–1065. http://dx.doi.org/10.1016/j.chembiol.2014.07.008 .
• Alberts, B., Johnson, A., Lewis, J., Raff, M., Roberts, K., and Walter, P. (2002). A pre-RNA world probably predates the RNA world. In Molecular biology of the cell (4th ed.). New York, NY: Garland Science. Retrieved from http://www.ncbi.nlm.nih.gov/books/NBK26876/#_A1124_ .
• Moran, L. A. (2009, May 15). Metabolism first and the origin of life. In Sandwalk: Strolling with a skeptical biochemist . Retrieved from http://www.simsoup.info/Origin_Landmarks_Oparin_Haldane.html .
• Kimball, J. W. (2015, May 17). The first cell? In Kimball's biology pages . Retrieved from http://www.biology-pages.info/A/AbioticSynthesis.html#TheFirstCell?
• Kimball, J. W. (2015, May 17). Molecules from outer space? In Kimball's biology pages . Retrieved from http://www.biology-pages.info/A/AbioticSynthesis.html#Molecules_from_outer_space? .
• Jeffs, W. (2006, November 30). NASA scientists find primordial organic matter in meteorite. In NASA news . Retrieved from http://www.nasa.gov/centers/johnson/news/releases/2006/J06-103.html .

Additional references:

Want to join the conversation.

• Upvote Button navigates to signup page
• Downvote Button navigates to signup page
• Flag Button navigates to signup page

• To save this word, you'll need to log in. Log In

heterotrophic

Definition of heterotrophic

Examples of heterotrophic in a sentence.

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'heterotrophic.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History

1893, in the meaning defined above

Dictionary Entries Near heterotrophic

heterotroph hypothesis

heterotropous

Cite this Entry

“Heterotrophic.” Merriam-Webster.com Dictionary , Merriam-Webster, https://www.merriam-webster.com/dictionary/heterotrophic. Accessed 27 May. 2024.

Medical Definition

Medical definition of heterotrophic.

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!

Can you solve 4 words at once?

Word of the day.

See Definitions and Examples »

Get Word of the Day daily email!

Popular in Grammar & Usage

More commonly misspelled words, commonly misspelled words, how to use em dashes (—), en dashes (–) , and hyphens (-), absent letters that are heard anyway, how to use accents and diacritical marks, popular in wordplay, the words of the week - may 24, flower etymologies for your spring garden, 9 superb owl words, 'gaslighting,' 'woke,' 'democracy,' and other top lookups, 10 words for lesser-known games and sports, games & quizzes.