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What evolutionary explanations are there for death?

What evolutionary explanations are there for death?


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I know death and cancer doesn't hurt humans' reproductive success. It's not helping either.

Why do we die? Why dying humans (all of us) are common? What's the point of dying?


Death is not only for humans. All 'complicated enough' organisms die (with a notable exception of Hydra, though you may argue when it comes to the complexity). It is is easier to create a new organism from scratch than to repair both internal factors (free radicals, metabolic by-products,… ) and external (physical damage, exposure to toxins,… ).

Underlying causes of death actually can be evolutionary beneficial. For example, shortening of telomeres offers protection against cancer (on a cellular level), but also bounds lifespan.

So actually they may be evolutionary competition (within the same species) of young and old. Mutations helping young but harming older may be preferred to the opposite ones.


Who is to say that having living Humans isn't hurting our reproductive success? Older non-reproducing humans cost the human network valuable resources and take up a sizeable portion of our living niche. Metabolically unstreamlined aged organisms are certainly not the most efficient and could potentially get in the way of better suited young'uns.


From a systemic point of view, if we wish to evolutionarily induce our descendants (descendants of the current human race on the whole) to live longer lives, we would need to pro-create later.

If the whole of human race enforced a statute that prohibits pro-creation before the age of 40, then two pronged dynamics would happen

  • only adults fit enough to pro-create after 40 would produce off-springs.
  • only off-springs born to parents older than 40 who are fit enough would survive.

Since, there is a high tendency of abnormality and low survival of off-springs born to parents of older ages, absence of resource contention and genetic dynamics would encourage the initial propagation of the rare few fit off-springs.

Hence, unnatural "natural selection" would encourage the propagation of humans of longer life-spans. Perhaps, a natural disaster or viral outbreak could discourage humans from pro-creating before age 40. Perhaps, high rates of abortion. So long as the human race does not die out due to such restrictions. Perhaps, to the satisfaction of conspiracy lovers, a secretive organisation carries out a plan every 100K years to raise the bar for child-bearing age.

Therefore, it might be less of a question of advantage and more of the effects of motivation. That current status where

  • high motivation for humans to pro-create early in life.
  • low motivation for humans to have more children as they wise-up by being tired of raising kids too early.

Therefore, since no such secret organisation exists, there is infinitesimally little motivation for the existence of a "super-virus" type of humans to exist.

There is no motivation for super-humans to exist, because the distribution of life-spans have crowded out the food and survival resources of any possible primeval super-human.


There is no evolutionary advantage to dying.

So you question should be rephrased as to why organism die at all? Why hasn't evolution come up with an immortal animal that lives forever?

Well nature has actually done that https://en.wikipedia.org/wiki/Turritopsis_dohrnii Behold the immortal jellyfish.

So if we do have immortal jellyfish… why aren't there immortal mice?

A possible answer is because mice get eaten by cats (and wolves, foxes, owls, toads, humans, etc) The idea goes like this… there is no point having genes that makes you immortal if the probability of you being eaten within 1 year approaches 100%. In fact, in such a situation, you would want genes that will allow you to have as many babies as possible before that one year is up, even if those genes result in your death (ie cancer from cells that are growing too fast in that rush to be an adult, heart problem, muscle degeneration, poor immune system… because the body has redirected all energy from repair to reproduction). Such a trade off is worth while, as you aren't going to be alive long enough to see the downside of those bad genes.

So if this idea is correct… if an animal has fewer predators (or none at all), the animal would live longer. And yes, we actually do see such examples.

A famous example are the Opossums of Sapelo Island. The Possums were isolated on a predator free island 9000 years ago and now live 25%-50% longer than their mainland cousins. The difference is hereditary.

https://books.google.com/books?id=yYwHDAAAQBAJ&pg=PT62&lpg=PT62&dq=Sapelo+Island+opossum+long+lived&source=bl&ots=4AHZcnd8_L&sig=9Wgka1-bVl1xzJTX2F-AJhF0Y-g&hl=en&sa=X&ved=0ahUKEwi506Kq7_7QAhUI6YMKHS3FBQ84ChDoAQgZMAA#v=onepage&q=Sapelo%20Island%20opossum%20long%20lived&f=false

Another possible example is that between bats and mice. Both are small animals of similar weight. And in general the smaller the animal, the faster it breeds and the shorter its life span. Bats are a noted exception from this the rule. Bats live a very long life span or their mass. Lifespan in the wild rangers from 10 years to 40 years depending on species. Compare that to 1 year for a mouse. The difference? Not metabolism… Not mass… Not climate. But predators. Mice have many predators. Bats very few.


One key concept to bear in mind is "mutational load". Over time, individuals accumulate mutations - for example, older fathers pass on more mutations than younger ones. Undesirable mutations need to be removed by natural selection each generation at at least the same rate as they accumulate, or a "mutational meltdown" occurs. The length of time between generations needs to be set so that the number of mutations purged by deaths is equal to the number that are introduced by mutation. Here is a rather interesting study providing some evidence for this point of view.

Note that infertility is "lethal" in genetic terms, so this concept in and of itself does not explain why a woman who passes menopause needs to die at any age. It seems easy to add further speculation here, so I'll leave that to the reader.


The evolutionary explanation is quite simple. Without death, evolution couldn't take place in the first place at all.

Who knows that jellyfish are immortal? Did they continuously evolve from one cell (without reproduction)? I don't think so. Who knows if today present jellyfish were already alive 1000 000 years ago (i.e. without parents)? I think this is the case for any living creature.

That's why telomeres get shorter and shorter when growing older. In the case of cancer, these telomeres stay the same with each division of the parent cell, so it grows wildly. Which all species would probably do so too.


# God is the creator, and evolution is compelling science

So what are the central ideas that define EC? ECs believe that God created and sustains all things. We believe that God acts purposefully in creation, just as he does in our lives, and that he continues to actively uphold and sustain creation. We believe in the Trinity, the full divinity and full humanity of Jesus Christ, and the bodily resurrection of Jesus Christ from the dead. We believe that all humans are made in the image of God and all humans have a sinful nature. We believe in salvation by grace through faith in Christ alone.

ECs accept evolution as the best scientific explanation we have for how life on Earth has changed over time. In biology, evolution refers to “descent with modification,” which includes the idea that all species are descended from a common ancestor over many generations. We therefore accept the scientific evidence that all life on Earth is related, including humans—which does not negate the image of God in us.

EC is neither science nor theology, but an explanatory system that seeks to incorporate the best scholarship from each. It also includes some ideas about how theology and science relate to one another. For how EC compares to other views on origins, see How is BioLogos different from Evolutionism, Intelligent Design, and Creationism?.


The Institute for Creation Research

Humans have always wondered about the meaning of life. life has no higher purpose than to perpetuate the survival of DNA. life has no design, no purpose, no evil and no good, nothing but blind pitiless indifference. 1 --Richard Dawkins

Evolution is "deceptively simple yet utterly profound in its implications," 2 the first of which is that living creatures "differ from one another, and those variations arise at random, without a plan or purpose." 3 Evolution must be without plan or purpose because its core tenet is the natural selection of the fittest, produced by random copying errors called mutations. Darwin "was keenly aware that admitting any purposefulness whatsoever to the question of the origin of species would put his theory of natural selection on a very slippery slope." 4 Pulitzer Prize author Edward Humes wrote that the fact of evolution was obvious but "few could see it, so trapped were they by the human&hellipdesire to find design and purpose in the world." He concluded:

Darwin's brilliance was in seeing beyond the appearance of design, and understanding the purposeless, merciless process of natural selection, of life and death in the wild, and how it culled all but the most successful organisms from the tree of life, thereby creating the illusion that a master intellect had designed the world. But close inspection of the watchlike "perfection" of honeybees' combs or ant trails&hellipreveals that they are a product of random, repetitive, unconscious behaviors, not conscious design. 5

The fact that evolution teaches that life has no purpose beyond perpetuating its own survival is not lost on teachers. One testified that teaching evolution "impacted their consciences" because it moved teachers away from the "idea that they were born for a purpose&hellip something completely counter to their mindset and beliefs." 6

In a study on why children resist accepting evolution, Yale psychologists Bloom and Weisberg concluded that the evolutionary way of viewing the world, which the authors call "promiscuous teleology," makes it difficult for them to accept evolution. Children "naturally see the world in terms of design and purpose." 7 The ultimate purposelessness of evolution, and thus of the life that it produces, was eloquently expressed by Professor Lawrence Krauss as follows: "We're just a bit of pollution&hellip. If you got rid of us&hellipthe universe would be largely the same. We're completely irrelevant." 8

The Textbooks

To determine what schools are teaching about religious questions such as the purpose of life, I surveyed current science textbooks and found that they tend to teach the view that evolution is both nihilistic and atheistic. One of today's most widely-used textbooks stated that "evolution works without either plan or purpose&hellip. Evolution is random and undirected." 9 Another text by the same authors added that Darwin knew his theory "required believing in philosophical materialism, the conviction that matter is the stuff of all existence and that all mental and spiritual phenomena are its byproducts." The authors continued:

Darwinian evolution was not only purposeless but also heartless--a process in which. nature ruthlessly eliminates the unfit. Suddenly, humanity was reduced to just one more species in a world that cared nothing for us. The great human mind was no more than a mass of evolving neurons. Worst of all, there was no divine plan to guide us. 10

Another text taught that humans are just "a tiny, largely fortuitous, and late-arising twig on the enormously arborescent bush of life" and the belief that a "progressive, guiding force, consistently pushing evolution to move in a single direction" is now known to be "misguided." 11 Many texts teach that evolution is purposeless and has no goal except to achieve brute survival: the "idea that evolution is not directed towards a final goal or state has been more difficult for many people to accept than the process of evolution itself." 12 One major text openly teaches that humans were created by a blind, deaf, and dumb watchmaker--namely natural selection, which is "totally blind to the future."

Humans. came from the same evolutionary source as every other species. It is natural selection of selfish genes that has given us our bodies and our brains&hellip. Natural selection&hellipexplains&hellipthe whole of life, the diversity of life, the complexity of life, |and| the apparent design in life." 13

The Implications

Many texts are very open about the implications of Darwinism for theism. One teaches that Darwin's immeasurably important contribution to science was to show that, despite life's apparent evidence of design and purpose, mechanistic causes explain all biological phenomena. The text adds that by coupling "undirected, purposeless variation to the blind, uncaring process of natural selection, Darwin made theological or spiritual explanations of the life processes superfluous." 14 The author concludes by noting that "it was Darwin's theory of Evolution that provided a crucial plank to the platform of mechanisms and materialism&hellipthat has been the stage of most western thought." 15 Another text even stated directly that humans were created by a random process, not a loving, purposeful God, and:

The real difficulty in accepting Darwin's theory has always been that it seems to diminish our significance&hellip. |Evolution| asked us to accept the proposition that, like all other organisms, we too are the products of a random process that, as far as science can show, we are not created for any special purpose or as part of any universal design. 16

These texts are all clearly teaching religious ideas, not science. An excellent example is a text that openly ruled out not only theistic evolution, but any role for God in nature, and demonstrated that Darwinism threatened theism by showing that humans and all life "could be explained by natural selection without the intervention of a god." Evolutionary "randomness and uncertainty had replaced a deity having conscious, purposeful, human characteristics."

The Darwinian view that&hellip present-type organisms were not created spontaneously but formed in a succession of selective events that occurred in the past, contradicted the common religious view that there could be no design, biological or otherwise, without an intelligent designer&hellip. In this scheme a god of design and purpose is not necessary&hellip. Religion has been bolstered by&hellip the comforting idea that humanity was created in the image of a god to rule over the world and its creatures. Religion provided emotional solace, a set of ethical and moral values&hellip. Nevertheless, faith in religious dogma has been eroded by natural explanations of its mysteries&hellip. The positions of the creationists and the scientific world appear irreconcilable." 17

Darwin himself taught a totally atheistic, naturalistic view of origins. He even once said, "I would give nothing for the theory of natural selection if it requires miraculous additions at any one stage of descent." 18 John Alcock, an evolutionary biologist, therefore concluded that "we exist solely to propagate the genes within us." 19

Leading Darwin scholar Janet Browne makes it very clear that Darwin's goal was the "arduous task of reorienting the way Victorians looked at nature." To do this Darwin had to convince the world that "ideas about a benevolent, nearly perfect natural world" and those that believe "beauty was given to things for a purpose, were wrong--that the idea of a loving God who created all living things and brought men and women into existence was&hellipa fable."

The world&hellipsteeped in moral meaning which helped mankind seek out higher goals in life, was not Darwin's. Darwin's view of nature was dark--black&hellip. Where most men and women generally believed in some kind of design in nature--some kind of plan and order--and felt a deep-seated, mostly inexpressible belief that their existence had meaning, Darwin wanted them to see all life as empty of any divine purpose. 20

Darwin knew how difficult it was to abandon such a view, but realized that for evolution to work, nature must ultimately be "governed entirely by chance." Browne concludes:

The pleasant outward face of nature was precisely that--only an outward face. Underneath was perpetual struggle, species against species, individual against individual. Life was ruled by death. destruction was the key to reproductive success. All the theological meaning was thus stripped out by Darwin and replaced by the concept of competition. All the telos, the purpose, on which natural theologians based their ideas of perfect adaptation was redirected into Malthusian--Darwinian--struggle. What most people saw as God-given design he saw as mere adaptations to circumstance, adaptations that were meaningless except for the way in which they helped an animal or plant to survive. 21

Neo-Darwinist Richard Dawkins recognized the purposelessness of such a system:

In a universe of blind physical forces and genetic replication some people are going to get hurt, other people are going to get lucky, and you won't find any rhyme or reason in it, nor any justice. The universe we observe has precisely the properties we should expect if there is, at bottom, no design, no purpose, no evil and no good, nothing but blind, pitiless indifference. 22

How widely is this view held by scientists? One study of 149 leading biologists found that 89.9 percent believed that evolution has no ultimate purpose or goal except survival, and we are just a cosmic accident existing at the whim of time and chance. A mere six percent believed that evolution has a purpose. 23 Almost all of those who believed that evolution had no purpose were atheists. This is only one example that Sommers and Rosenberg call the "destructive power of Darwinian theory." 24

Purpose and Christianity

Christianity teaches that God made the universe as a home for humans. If the universe evolved purely by natural means, then it just exists and any "purpose" for its existence can only be that which humans themselves attribute to it. But our own experience and intellectual attainments argue against this. The similarity of human-constructed machines and the orderly functioning of the universe is the basis of the design argument. Just as a machine requires a designer and a builder, so too the universe that we see requires a designer and a builder.

Determining the purpose of something depends on the observer's worldview. To a nontheist the question "What is the purpose of a living organism's structure?" means only "How does this structure aid survival?" Eyesight and legs would therefore have nothing to do with enjoyment of life they are merely an unintended byproduct of evolution. Biologists consistently explain everything from coloration to sexual habits solely on the basis of survival. Orthodox neo-Darwinism views everything as either an unfortunate or a fortuitous event resulting from the outworking of natural law and random, naturally-selected mutations. Conversely, creationists interpret all reality according to beliefs about God's purpose for humans. Evolutionists can usually explain even contradictory behavior, but creationists look beyond this and try to determine what role it plays in God's plan.

Conclusions

Orthodox evolution teaches that the living world has no plan or purpose except survival, is random, undirected, and heartless. Humans live in a world that cares nothing for us, our minds are simply masses of meat, and no divine plan exists to guide us. These teachings are hardly neutral, but rather openly teach religion--the religion of atheism and nihilism. The courts have consistently approved teaching this anti-Christian religion in public schools and have blocked all attempts to neutralize these clearly religious ideas.

As the Word of God states, "For the time will come when they will not endure sound doctrine but after their own lusts shall they heap to themselves teachers, having itching ears And they shall turn away their ears from the truth, and shall be turned unto fables" (2 Timothy 4:3-4).

  1. Scheff, Liam. 2007. The Dawkins Delusion. Salvo, 2:94.
  2. Humes, Edward. 2007. Monkey Girl: Evolution, Education, Religion, and the Battle for America's Soul. New York: Ecco, 119.
  3. Ibid, 119.
  4. Turner, J. Scott. 2007. The Tinkerer's Accomplice: How Design Emerges from Life Itself. Cambridge, MA: Harvard University Press, 206.
  5. Humes, Monkey Girl, 119.
  6. Ibid, 172.
  7. Bloom, Paul and Deena Skolnick Weisberg. 2007. Childhood Origins to Adult Resistance to Science. Science, 316:996.
  8. Panek, Richard. 2007. Out There. New York Times Magazine, 56.
  9. Miller, Kenneth R. and Joseph S. Levine. Biology. 1998. Fourth Edition, Englewood Cliffs, NJ: Prentice Hall, 658, emphasis in original.
  10. Levine, Joseph S. and Kenneth R. Miller 1994. Biology: Discovering Life. Second Edition, Lexington, MA: D.C. Heath, 161, emphasis in original.
  11. Raven, Peter H. and George B. Johnson. 2002. Biology. Sixth Edition, Boston, MA: McGraw Hill, 16, 443.
  12. Purves, William K., David Sadava, Gordon H. Orians, and H. Craig Keller. 2001. Life: The Science of Biology. Sixth Edition, Sunderland, MA: Sinauer Associates W.H. Freeman, 3.
  13. Interview with Richard Dawkins in Campbell, Neil A., Jane B. Reece, and Lawrence G. Mitchell. 1999. Biology. Fifth Edition, Menlo Park, CA: Addison Wesley Longman, 412-413.
  14. Futuyma, Douglas J. 1998. Evolutionary Biology. Third Edition, Sunderland, MA: Sinauer Associates, 5.
  15. Ibid, 5.
  16. Curtis, Helena and N. Sue Barnes. 1981. Invitation to Biology. Third Edition, New York, NY: Worth, 475.
  17. Strickberger, Monroe. 2000. Evolution. Third Edition, Sudbury, MA: Jones & Bartlett, 70-71.
  18. Darwin, Francis (editor). 1888. The Life and Letters of Charles Darwin. London: John Murray, 210.
  19. Alcock, John. 1998. Animal Behavior: An Evolutionary Approach. Sunderland, MA: Sinauer Associates, 16, 609.
  20. Browne, Janet. 1995. Charles Darwin: Voyaging, A Biography. Princeton, New Jersey: Princeton University Press, 542.
  21. Ibid, 542.
  22. Dawkins, Richard. 1995. River Out of Eden. New York: Basic Books, 133.
  23. Graffin, Gregory W. 2004. Evolution, Monism, Atheism, and the Naturalist World-View. Ithaca, NY: Polypterus Press, 42.
  24. Sommers, Tamler and Alex Rosenberg. 2003. Darwin's Nihilistic Idea: Evolution and the Meaningless of Life. Biology and Philosophy, 18:653.

* Dr. Bergman is Professor of Biology at Northwest State College in Ohio.

Cite this article: Bergman, J. 2007. Darwinism: Survival without Purpose. Acts & Facts. 36 (11): 10.


Sex and Death

Is the history of life a series of accidents or a drama scripted by selfish genes? Is there an "essential" human nature, determined at birth or in a distant evolutionary past? What should we conserve—species, ecosystems, or something else?

Informed answers to questions like these, critical to our understanding of ourselves and the world around us, require both a knowledge of biology and a philosophical framework within which to make sense of its findings. In this accessible introduction to philosophy of biology, Kim Sterelny and Paul E. Griffiths present both the science and the philosophical context necessary for a critical understanding of the most exciting debates shaping biology today. The authors, both of whom have published extensively in this field, describe the range of competing views—including their own—on these fascinating topics.

With its clear explanations of both biological and philosophical concepts, Sex and Death will appeal not only to undergraduates, but also to the many general readers eager to think critically about the science of life.

Preface
Part I - Theory Really Matters: Philosophy of Biology and Social Issues
1.1. The Science of Life Itself
1.2. Is There an Essential Human Nature?
1.3. Is Genuine Altruism Possible?
1.4. Are Human Beings Programmed by Their Genes?
1.5. Biology and the Pre-emption of Social Science
1.6. What Should Conservationists Conserve?
2. The Received View of Evolution
2.1. The Diversity of Life
2.2. Evolution and Natural Selection
2.3. The Received View and Its Challenges
Part II - Genes, Molecules, and Organisms
3. The Gene’s Eye View of Evolution
3.1. Replicators and Interactors
3.2. The Special Status of Replicators
3.3. The Bookkeeping Argument
3.4. The Extended Phenotype
4. The Organisim Strikes Back
4.1. What Is a Gene?
4.2. Genes Are Active Germ Line Replicators
4.3. Genes Are Difference Makers
5. The Developmental Systems Alternative
5.1. Gene Selectionism and Development
5.2. Epigenetic Inheritance and Beyond
5.3. The Interactionist Consensus
5.4. Information in Development
5.5. Other Grounds for Privileging Genes
5.6. Developmental Systems and Extended Replicators
5.7. One True Story?
6. Mendel and Molecules
6.1. How Theories Relate: Displacement, Incorporation, and Integration
6.2. What Is Mendelian Genetics?
6.3. Molecular Genetics: Transcription and Translation
6.4. Gene Regulation
6.5. Are Genes Protein Makers?
7. Reduction: For and Against
7.1. The Antireductionist Consensus
7.2. Reduction by Degrees?
7.3. Are Genes DNA Sequences Plus Contexts?
7.4. The Reductionist Anticonsensus
Part III - Organisms, Groups, and Species
8. Organisms, Groups, and Superorganisms
8.1. Interactors
8.2. The Challenge of Altruism
8.3. Group Selection: Take 1
8.4. Group Selection: Take 2
8.5. Population-Structured Evolution
8.6. Organisms and Superorganisms
9. Species
9.1. Are Species Real?
9.2. The Nature of Species
9.3. The One True Tree of Life
9.4. Species Selection
Part IV - Evolutionary Explanations
10. Adaptation, Perfection, Function
10.1. Adaptation
10.2. Function
10.3. The Attack on Adaptationism
10.4. What Is Adaptationism?
10.5. Structuralism and the Bauplan
10.6. Optimality and Falsifiability
10.7. Adaptation and the Comparative Method
11. Adaptation, Ecology, and the Environment
11.1. The Received View in Ecology
11.2. History and Theory in Ecology
11.3. The Balance of Nature
11.4. Niches and Organisms
11.5. Reconstructing Niches
11.6. Unfinished Business
12. Life on Earth: The Big Picture
12.1. The Arrow of Time and the Ladder of Progress
12.2. Gould’s Challenge
12.3. What Is Disparity?
12.4. Contingency and Its Consequences
12.5. Mass Extinction and the History of Life
12.6. Conclusions
Part V - Evolution and Human Nature
13. From Sociobiology to Evolutionary Psychology
13.1. 1975 and All That
13.2. The Wilson Program
13.3. From Darwinian Behaviorism to Darwinian Psychology
13.4. Evolutionary Psychology and Its Promise
13.5. Evolutionary Psychology and Its Problems
13.6. Memes and Cultural Evolution
14. A Case Study: Evolutionary Theories of Emotion
14.1. Darwin on the Emotions
14.2. Sociobiology and Evolutionary Psychology on the Emotions
14.3. The Modular Emotions
14.4. Beyond the Modular Emotions
14.5. Emotion, Evolution, and Evolved Psychology
Part VI - Concluding Thoughts
15. What Is Life?
15.1. Defining Life
15.2. Universal Biology
15.3. Simulation and Emergence
Final Thoughts
Glossary
References
Index


4. Evolution Has Never Been Observed

This one is a lot like the previous one. It is simply a false statement that relies on a misunderstanding of evolution to lend it some credibility. If you believe in the comic book superhero version of evolution (individuals evolving) or the idea that whole species collectively evolve, then you might be able to buy what creationists are selling.

In reality, we observe evolution at work all the time. When we spray pesticides and future generations of insects become immune, that is evolution. When we use medications and future generations of bacteria become immune, that is evolution. Once again when we go back to how humans have domesticated animals and plants over thousands of years that are evidence of evolution as well. All observable and easy to draw conclusions from.


Evidence of Evolution

  • If today's species came from ancient species, the we should be able to find remains of those species that no longer exist.
  • We have tons of fossils of creatures that no longer exist but bear striking resemblance to creatures that do exist today.
  • Carbon dating--gives an age of a sample based on the amount of radioactive carbon is in a sample.
  • Fossil record---creates a geologic time scale.

2. Evidence from Living Organisms

  • Evidence of Common Ancestry --Hawaiin Honeycreeper
  • Homologous Structures--structures that are embryologically similar, but have different functions, the wing of a bird and the forearm of a human
  • Vestigial Organs--seemingly functionless parts, snakes have tiny pelvic and limb bones, humans have a tail bone
  • Biochemistry and DNA
  • Embryological development--Embryos of different species develop almost identically
  • Direct Observation of species change (wolves/dogs, peppered moths)

1. industrial melanism (Kettlewell's moths)
2. dog breeds
3. viruses & vaccines
4. bacteria & antibiotics
5. elepant tusks

/>This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.


A most private evolution: dumb designs for sex: evolutionary biology walks on the weird side.

Maybe female seed beetles have their own what-the-bleep exclamation. Even for insects, it's difficult to imagine any other reaction to a male Callosobruchus maculatus beetle's sex organ, which has spikes.

"It jumps to mind as something quite dumb," says Goran Arnqvist, an evolutionary biologist at Uppsala University in Sweden, who for much of the past eight years has studied seed beetle sex.

Male beetles of several Callosobruchus species have sharp edges on their sperm-delivery organs. The females' ducts grow a bit of extra toughening but not enough to make sex safe from the risk of injury. After many tests, Arnqvist has concluded that the genital excesses aren't good for the species as a whole. These seed beetles would have less-damaging sex--and would produce more babies--if males lost their edges.

Discussions of evolution often glorify the beautifully apt forms: orchids with nectar recesses just the right length for the tonguelike structure of a certain moth, or harmless butterflies with the same wing colors as a poisonous neighbor. Yet the most dramatic examples of the power of evolutionary theory may come from the strange and ugly stuff--biology that seems too dumb to have been designed.

Trying to understand counterintuitive sexual parts and habits follows in the best of scientific traditions. As Charles Darwin worked on evolution, he pondered male phenomena that looked useless, or even harmful, for surviving. Outsized horns on male beetles puzzled him, as did male birds with gorgeous plumage.

Out of this consternation came his insight into a process he called sexual selection, which he distinguished from natural selection. There may be survival of the fittest, but there's also survival of the sexiest.

Today the sex-related selection process doesn't get much attention outside scientific circles, but it's a powerful tool for making sense of downright peculiar stuff. Arnqvist and other biologists are expanding Darwin's framework, exploring the counterintuitive aspects of sex from flirtation to family life. And theorists are discussing female behavior that Darwin never recognized, or perhaps just didn't care to discuss in print.

When Darwin first put his full idea of natural selection into print, he knew it wasn't enough. In 1859, he argued in On the Origin of Species that organisms best adapted to their environment survive in greater numbers and leave more offspring than do their less fit neighbors. Thus more suitable traits gradually replace clunkier versions.

Yet antlers on stags and tails on peacocks could hardly be adaptations to the environment. Both antlers and tails may be so familiar that it takes a minute to summon a sense of their absurdity. They're huge. They must drain energy to produce. There's no way they improve agility in locomotion or foraging.

"The sight of a feather in a peacock's tail, whenever I gaze at it, makes me sick!" Darwin wrote in a letter to the botanist Asa Gray, albeit in a whimsical paragraph. Nauseated or not, Darwin was willing to step beyond survival of the fittest.

He devoted a few pages in the Origin to introduce sexual selection as a sort of wild-oats younger brother of natural selection. Sexual selection, as Darwin formulated it in the sixth edition of Origin, depends "not on the struggle for existence in relation to other organic beings or to external conditions, but on a struggle between the individuals of one sex, generally the males, for possession of the other."

Antlers evolved as stag-on-stag weaponry for fights over a female, he argued. Males also compete in contests "of a more peaceful character," he wrote. Extravagant plumage, singing and what he called "strange antics," such as bird acrobatic displays, bedazzle a female into choosing one male over his rivals.

What's good for bedazzling can be bad for survival, of course. Darwin made a glancing allusion to the conflict in his 1871 work, The Descent of Man, and Selection in Relation to Sex. There he admits that sexy traits could be slightly harmful to the male.

Harm may be part of the charm, although debate continues on how supersized, shimmery tails evolved. The year 2008 proved a lively one for peacock studies, as a long-term line of research met a challenge from a new one.

Three independent studies in the past 20 years have found that tails matter. For example, Marion Petrie of Newcastle University in England and a colleague turned the same birds from hotties to notties and back again by clipping some of the eyespots out of the males' tails and then reattaching the finery. The females probably weren't counting male spots, but were choosing males that displayed a greater density of spots, according to similar tests by Adeline Loyau, now at France's CNRS Moulis station.

Peahens' interest in eyespots could have arisen for no particularly practical reason, Petrie and Loyau speculate. Their idea draws on the concepts of sensory bias and sensory exploitation, which deal with an apparently arbitrary silliness at the heart of sexy traits. Sure, a blue spot now burns hot with allure. But biologists puzzle over why a purple stripe didn't evolve instead.

In this scenario, basic arbitrary-looking evolutionary directions (blue not purple long tail, not wide eyes) actually were arbitrary as far as mate choice goes. For some reason that had nothing to do with reproduction, females might have tended to notice a particular color or shape or motion.

Let's imagine it was a blue spot. Males exploit that predisposition, as guys with even a modest dot attract extra female attention. If the female bias gets inherited along with male coloring, then off go the males in an evolutionary race for bigger, better, bluer blues.

That kind of scenario might have begun the peacock's tale. At some point, the story goes, tails grew so fancy they posed a handicap for males. Growing the best tail or keeping it flossy or managing a little sprint despite its weight demanded energy or vitamin-rich food or something otherwise limited. And in animal communication, that's when fashion starts to mean something.

What's called the handicap principle comes from the Israeli biologist Amotz Zahavi, now retired from Tel Aviv University, who thought about how creatures judge each other's quality.

Suppose the peacock's tail signals, "Hey, honey. I'm the best bird, and you need me right now." Such a tail stays reliable as a badge of quality across generations only if good tails present a handicap that not all individuals can overcome, Zahavi suggested. A robust bird can pay the cost and still look good. A puny bird can't compensate for the loss, and looks like a second-rater. The tail signal honestly indicates quality.

A signal with no cost, Zahavi argued, means anybody could waggle a full rainbow rear. Everybody could signal "best bird." The signal would lose its utility and fade away over generations, or never evolve to begin with.

Petrie and others have been taking this signaling idea further, testing to see whether the tail might signal good genes or some true benefit for a female who mates with a showy male. It sure isn't help with the chores and the chicks. Peacocks do only the most basic task of fatherhood.

In a jolt after years of research linking female preferences to tail feathers, readers of the journal Animal Behaviour were startled to learn last April that a seven-year study of feral peacocks in a park near Shizuoka, Japan, found no sign that females were choosing males based on their tails. Neither eyespot number, tail symmetry nor tail length correlated with a male's success or his health, reported Mariko Takahashi of the University of Tokyo and her colleagues.

Loyau, Petrie and two other researchers responded in the November issue with ideas about why the new study doesn't agree with old research.

For one thing, the researchers point out, the new study took place on the opposite side of the world. Other animal studies have recently detected what's called adaptive plasticity in mate choice, or differences in how various groups of females of the same species choose mates. What's a useful signal in one environment may not matter much in another.

Also, Loyau says, "If we really want to understand, we need to study peacocks in the wild."

One commentary isn't going to settle a matter that's been under study since it nauseated Darwin, though. The Japanese study's challenge to years of experiment, theory and assumption is "sure to prove controversial," predicts Louise Barrett, one of the journal's editors.

Plausible explanations for a dazzling but impractical tail don't make sense for injurious genital spikes. Beetle genitalia look more like instruments of war. The latest research suggests warfare may be the point.

In Darwin's writings, males fought males. Now researchers recognize that males and females clash too.

As Arnqvist puts it, "Unless you have perfect monogamy, there are conflicts of interest." When a male and a female can take different strategies in mating, their best interests often differ. What's good for the goose in terms of how often to mate, with whom and for how long probably won't be best for the gander.

Thus human scientists confront the question of how to spot battles of the sexes in other species. In a 2000 paper in Nature titled "Genital damage, kicking and early death," two researchers reported evidence that seed beetle mating might have more conflict than concord. Helen Crudgington and Mike Siva-Jothy of the University of Sheffield in England timed beetle mating that takes place on black-eyed peas. After about three minutes, females start slamming their hind legs against the male. A typical mating encounter lasts about four minutes.

When the researchers removed females' legs so they couldn't kick, males persisted around six minutes. The sexes appear to disagree about how much is enough.

Female beetles' kickoffs probably are not a way of reducing contact with wimpy males that can't stand a drubbing, Siva-Jothy says. Female seed beetles look as if they have genuine cause to minimize mating. The longer an encounter lasted, the more rips and tears Siva-Jothy and Crudgington found in the female reproductive tract. And as additional evidence of harm, females that mated only once during the experiment lived longer than females that mated twice.

Those harmful male sex organs in the beetles "look like medieval torture instruments," Arnqvist says. Yet such a device may not have evolved through any direct benefit of its power to injure. Instead, injuries are probably side effects, Arnqvist contends.

He and his colleagues have tested for potential direct benefits for the male, including what's called the "terminal investment." In a terminal investment, a mauled creature facing an uncertain or shortened life span throws all resources and effort into the current batch of young. A dad with no guarantee he'll sire one of mom's future clutches will certainly benefit if he can get her to make an all-out investment in his offspring right then.

Exactly mimicking the damage of mating isn't possible, so Arnqvist and his colleagues inflicted other injuries, including body punctures or cuts on wings, after a group of females had mated. The injured females actually laid fewer eggs than intact moms did, so Arnqvist dismissed the idea of a terminal investment bonus for the males. Also, the damaged females tended to mate again sooner than usual, so the damage doesn't appear to be a roundabout way of foiling rivals.

To explain how the sharp edges of a seed beetle arose without direct benefits, Arnqvist proposes that some quirk of male physiology, such as an irregular surface to improve anchoring injured females incidentally. The risk of such injuries favored females with tougher plumbing which in turn favored spikier males. So seed beetle anatomy, he argues, could derive from an ongoing arms race between the sexes, even if the conflict harms the species.

Similar harm, and possibly arms races, could be smoldering far beyond seed beetles. "Being an entomologist, I know of hundreds of insect groups with male genitalia that have this appearance," Arnqvist says.

Some male insects deploy bundles of spines, knives and even full-fledged swords. Male bedbug organs look like a stiletto, and "they literally use it as a stiletto," Arnqvist says. Females' reproductive tracts do have external openings, but male bedbugs usually just stab through some spot in the body wall and let the sperm swim from there.

Birds have evolutionary arms races too, says Patricia Brennan of Yale University. Most birds don't have insertable parts, achieving fertilization by the so-called cloacal kiss. It's just his-to-hers contact of cloacae, the all-purpose openings of reproductive and excretory systems. Male ducks, however, belong among the 3 percent of male bird species with a phallus some duck organs extend 40 centimeters.

In the mallard and long-tailed duck, males deploy at unusual length "what looks like a weird tentacle with bumps and ridges," Brennan says.

Female duck anatomy hadn't received as detailed a look until Brennan spent some time in Tim Birkhead's lab at the University of Sheffield. Female mallards and long-tailed ducks have a correspondingly intricate reproductive tract "like a maze," Brennan says.

In studying 16 species, she found that if the male had a long and elaborate phallus, the female had intricate genitals too. The sexes' intricacies seemed at odds with each other, however. Males spiraled counterclockwise (from the base) but female reproductive tracts antagonistically curved clockwise (from the outer opening). Blind pouches along the female tracts looked like traps for sperm.

A classic arms race is what Brennan and Birkhead proposed in PLoS ONE in May 2007 to explain the mismatched genitalia. Males of the extra-long species are more likely to try forcing themselves on females than are less elaborated males. Thus females might have benefited from countermeasures against unsuitable matings. A maze that proves navigable only when a female cooperates and relaxes could have provided some control, but it would also favor the evolution of even more extreme males.

"These kinds of evolutionary races are costly," Brennan says. "You would have been better off without this conflict in the first place, but you can't stop investing because you're already in the war."

There's chemical warfare too, says William Rice of the University of California, Santa Barbara. Male fruit flies dope their seminal fluids with a cocktail of additives that revs up the female so she devotes extra resources to the eggs. Never mind that it shortens her life and therefore shrinks the total number of offspring she can produce.

Possible high-quality offspring won't make up for loss in quantity, Rice and his colleagues report in the November Journal of Evolutionary Biology. They tested the idea that mating with a male carrying superb genes might, over the course of generations, give a female enough extra grandkids and great-grandkids to compensate for her initially small brood.

Yet breeding experiments showed that good genes don't help enough, the researchers conclude. At most, females mating with a superior male might get a modest increase in the number of their offspring's descendants. The uptick isn't big enough to compensate for the downside of drugged sperm. This evidence and earlier work show fruit flies paying a toll for their battle of the sexes. "It's clearly bad for the species," Rice says.

Even hermaphrodites can have battles of the sexes. Conflicts arise when everybody tries to play the guy instead of the girl, according to ongoing work by Nico Michiels and Nils Anthes of the University of Tubingen in Germany.

Just why it would be better to be "male" has inspired much theorizing about sperm being energetically cheaper than eggs to produce. Anthes, though, does the accounting in different terms. He sees conflicts looming if one sex, usually the male, benefits from virtually unlimited matings while the other sex rapidly reaches some limit. Females, for example, might be able to produce only so many eggs in a lifetime, so attempts to fertilize even more eggs wouldn't be useful.

Whatever drives the conflicts, researchers see what looks like a lot of antagonism out there. In the small marine flatworm Pseudoceros bifurcus, two flatworms stand up on the hind parts of their bodies, stick out both their penises (each worm has two) and jab them at each other. Worms bend and dodge as any duelists would, trying for a hypodermic strike that injects sperm anywhere on the opponent's body. Bouts sometimes last 20 minutes.

In the flatworm Pseudobiceros bedfordi, ejaculate dissolves its way through skin and can leave scars. A full splash can dissolve the recipient into two pieces, although the flatworms do regenerate lost body parts.

The latest battle that Michiels and Anthes have documented "turned out to be quite spectacular," Anthes says. Hermaphroditic Siphopteron quadrispinosum sea slugs stab at each other with a sharp spike on the side of the penis. When one slug gets spiked in the head region, it slows down and stops dueling. The target looks "pretty sleepy," Anthes says. The spiker is apparently injecting some kind of sedative that allows unilateral insemination, Anthes and Michiels reported in 2007 in Biology Letters.

Counterintuitive reproductive strategies continue even into parenthood. Consider the penduline tits (Remiz pendulinus). In any given nest, the mother and/or the father often desert and start a second family, says Tamas Szekely of the University of Bath in England. A single parent can still raise chicks to adulthood, given the right location, but sometimes both parents desert. In these cases, the chicks starve. In populations across Europe, about a third of egg clutches die from abandonment, Szekely and his colleagues have found.

To make sense of this, Szekely describes a competitive desertion arms race between male and female tits. Each sex can increase its number of offspring by starting another nest with a new partner, as long as the old partner stays around to care for the previous clutch.

As the optimal time for desertion nears, when all eggs have been laid, female tits behave as if they're trying to keep their current mate from seeing the true number of eggs. Females confront a male at the nest opening and fuss at him furiously.

Whether this loss of a third of clutches ends up as a bad thing for the species overall will take more research, says Istvan Szentirmai at Orseg National Park in Hungary. But he speculates that the strategy limits the species to insect-rich places like wetlands, where a single parent can catch all the necessary baby food.

Mothers certainly didn't run off with other males in On the Origin of Species. Darwin acknowledged that males of various species take more than one mate but said hardly anything about such shocking behavior (to mores of the era) in females. So one of the biggest developments in the theory of sexual selection has been the recognition that females in many species aren't monogamous, says Jeanne Zeh of the University of Nevada, Reno.

"It's molecular genetics," says David Zeh, also at Reno. Once DNA analysis could identify the true fathers of offspring, biologists could see widespread challenges to old ideas of females as the choosy, monogamous sex. That idea opens the way for much entertaining science.

Reproduction in the modern view isn't particularly pretty. With medieval torture instruments, mazes and corkscrews, drugged sperm and arms races everywhere, reproduction looks more like war than love. All in all, it's easy to wonder if sex itself was such a great idea.


Developmental plasticity and evolutionary explanations

Correspondence Tobias Uller, Department of Biology, Lund University, Sölvegatan 37, 22362 Lund, Sweden.

Department of Biology, Lund University, Lund, Sweden

Department of Biology, Lund University, Lund, Sweden

Current address: Reinder Radersma, Biometris, Wageningen University & Research, Droevendaalsesteeg 1, 6708 PB Wageningen, The Netherlands.

Department of Biology, Lund University, Lund, Sweden

Department of Biology, Lund University, Lund, Sweden

Institute for Life Sciences/Department of Computer Science, University of Southampton, Southampton, United Kingdom

Department of Biology, Lund University, Lund, Sweden

Correspondence Tobias Uller, Department of Biology, Lund University, Sölvegatan 37, 22362 Lund, Sweden.

Department of Biology, Lund University, Lund, Sweden

Department of Biology, Lund University, Lund, Sweden

Current address: Reinder Radersma, Biometris, Wageningen University & Research, Droevendaalsesteeg 1, 6708 PB Wageningen, The Netherlands.

Department of Biology, Lund University, Lund, Sweden

Department of Biology, Lund University, Lund, Sweden

Institute for Life Sciences/Department of Computer Science, University of Southampton, Southampton, United Kingdom

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Abstract

Developmental plasticity looks like a promising bridge between ecological and developmental perspectives on evolution. Yet, there is no consensus on whether plasticity is part of the explanation for adaptive evolution or an optional “add-on” to genes and natural selection. Here, we suggest that these differences in opinion are caused by differences in the simplifying assumptions, and particular idealizations, that enable evolutionary explanation. We outline why idealizations designed to explain evolution through natural selection prevent an understanding of the role of development, and vice versa. We show that representing plasticity as a reaction norm conforms with the idealizations of selective explanations, which can give the false impression that plasticity has no explanatory power for adaptive evolution. Finally, we use examples to illustrate why evolutionary explanations that include developmental plasticity may in fact be more satisfactory than explanations that solely refer to genes and natural selection.

Research Highlights

An accessible introduction to the use of idealization in evolutionary biology.

Shows why idealizations designed to explain evolution through natural selection prevent an understanding of the role of development, and vice versa.

Illustrates why evolutionary explanations that include developmental plasticity can be more satisfactory than explanations that solely refer to genes and natural selection.


About Me

Dr. Amy Tuteur is an obstetrician gynecologist. She received her undergraduate degree from Harvard College in 1979 and her medical degree from Boston University School of Medicine in 1984. Dr. Tuteur is a former clinical instructor at Harvard Medical School. She left the practice of medicine to raise her four children. Her book, How Your Baby Is Born, an illustrated guide to pregnancy, labor and delivery was published by Ziff-Davis Press in 1994. She can be reached at DrAmy5 at aol dot com.

E-mail: DrAmy5 at AOL dot com


The Biology of Death: Origins of Mortality

It may come as a surprise for you to learn (I know it did for me) that science is not quite certain as to why we die. I mean generally. In each specific case a cause of death is usually made: heart attack, cancer, gunshot wound, etc. But as far as why human beings in general die rather than go on living indefinitely, the answer is murky.

It used to be the case (and perhaps still is) that coroners would cite "natural causes" as the cause of the death of certain old Why we die, technically explained

It may come as a surprise for you to learn (I know it did for me) that science is not quite certain as to why we die. I mean generally. In each specific case a cause of death is usually made: heart attack, cancer, gunshot wound, etc. But as far as why human beings in general die rather than go on living indefinitely, the answer is murky.

It used to be the case (and perhaps still is) that coroners would cite "natural causes" as the cause of the death of certain old people. However in some places this is no longer allowed since science has established that there is no such thing as the nebulous "natural causes." If the medical examiner looks closely enough it will always be found that some part or parts of the body failed for one reason or another and should be cited as the cause of death.

Some people think we die (theoretically) because it is good for the species. Some people think we die because it is programmed into our cells to die. Others think we die because our bodies wear out. These are proximate reasons perhaps, but they do not explain why the evolutionary mechanism does not allow us to be immortal. The authors recall the idea that death is a byproduct of sexuality, noting that dividing nonsexual bacteria, for example, are theoretically immortal (as are cancer cells). They also point out that many species (salmon, for example) die immediately after reproduction. They cite studies showing that such species may go on living if they do not reproduce. Furthermore, they note that natural selection works most effectively when the organism is at or near sexual maturity. The further the organism gets from the onset of sexual maturity, the less effect natural selection has on making it adaptive that is, making it healthy and effective in warding off dangers from the environment.

This is really a fine explanation for why we die, and one that is cited by all the authorities I have read. Put another way, what it means is that the evolutionary mechanism "cares" less about older organisms that are no longer sexually reproductive than it does about younger ones that are. Or put still another way, the harmful mutations that would be selected against in younger organisms are not selected against in older individuals because those individuals are so few in number, relatively speaking (and more generally), because they produce so few offspring, the effect of their genes is small in the overall gene pool. I think it can be added that the young are better adapted (if only slightly, and in general) to the environment and therefore should be expected to out-reproduce the old.

If this is not clear, let me say that I did not understand these subtle points for a long time. Furthermore, they seem to beg the question of why the evolutionary mechanism does not allow organisms to continue to reproduce as they get older. In lobsters, the authors point out, their reproductive capability actually increases with age, and indeed this is understood as being one reason they live relatively long lives.

A more profound way of looking at this conundrum was suggested by G.C. Williams who explains that a flying fish always falls back into the water and that natural selection does nothing and needs to do nothing to return the fish to the water. (Gravity does it!--and note that gravity is in this example analogous to the natural forces--accident, predation, disease, etc.--that will eventually kill an organism.) What natural selection works on is making the fish more effective at staying in the air longer. Eventually however the fish must return to the water. The authors explain, "Natural selection gives the organism the means. to remain alive longer than if it were abandoned only to physical forces. these means are inevitably limited. Again, they can only delay the final outcome." (p. 188)

The authors further explain that "natural death has no value in and of itself [giving the lie to the good-for-the-species argument] its existence is simply the result of a central biological pointlessness to repair systems that would prevent aging. All. organisms. are doomed to exist temporarily. and the time they have to procreate cannot be extended indefinitely. Natural selection 'judges' each organism by the yardstick of procreation. The goal is successful reproduction. [even if it leads to a shortened lifespan]." Consequently, "[w]ithout going to the extreme examples of mayflies or salmon, this arrangement leads the organism to neglect itself just enough so that aging and natural death occur." (pp. 182-183)

Another point is that programmed cell death (apoptosis) is NOT the cause of the death of the organism. In fact, apoptosis works in exactly the opposite direction: the death of certain cells is for the betterment of the organism, as the authors argue in Chapter Six.

This is the fourth book I have read on this subject. The other three books are: Austad, Steven N. Why We Age: What Science Is Discovering about the Body's Journey Through Life [1997)] Clark, William R. A Means to an End: The Biological Basis of Aging and Death [1999] and Hayflick, Leonard. How and Why We Age [1994]. This book is more technical than the others and is more clearly aimed at the professional scientist. I would recommend it least except for the fact that it is the most current. For those interested in what is going on at the cellular and molecular levels in research, this book is perhaps the best choice.

--Dennis Littrell, author of “Understanding Evolution and Ourselves”
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