What good is a virus?

http://toddcwood.blogspot.com/2020/04/ask-creationist-about-viruses.html

What is a species?

From Appendix B in Species: A History of the Idea (2nd ed.) by John Wilkins:

Biological information

In this post I'm going to talk about biological information, which in turn is relevant in debates over evolution.

However this post is just an introduction. As such I'm going to simplify a lot of things. I realize I'm sacrificing technical accuracy but I'm doing so in order to get some main ideas across for those who might have zero background in all this but who wish to be able to make a foray into the debate over evolution.

Without further ado:

What lies at the heart of every living thing is not a fire, warm breath, not a 'spark of life'. It is information, words, instructions. If you want a metaphor, don't think of fires and sparks and breath. Think, instead, of a billion discrete digital characters carved in tablets of crystal. If you want to understand life, don't think about vibrant, throbbing gels and oozes, think about information technology.

(Richard Dawkins, "The power and the archives", The Blind Watchmaker)

1. Let's start with a book, computer code, and DNA:

   A book contains pages and text, but the pages are just paper and the text is just ink. Rather it's the words that convey the story. Not the words as text, but the words as information.

   A computer program contains code, but code is fundamentally just a pattern of binary digits: 0s and 1s. Rather it's code as a set of instructions for a computer to execute that makes a program functional. Hence code isn't merely bits but code is information.

   The DNA molecule contains four bases (adenine, cytosine, thymine, guanine), but these bases are ultimately atoms (e.g. carbon, hydrogen, oxygen, nitrogen), and atoms are just physical particles. Rather DNA (as genes) is biological information which can be transcribed and translated to build an organism.

2. These aren't mere arguments from analogy (pace Dawkins). I'm not saying text is like code which is like DNA. Rather this is a comparison of information. I'm suggesting the common denominator in all three is information.

3. Yet information is invisible. We can't sense it, not directly, but it exists. How does that work on atheism/naturalism and evolution/neo-Darwinism?

4. An atheist like Dawkins might argue information emerges from physical properties. Such as in the arrangement of words, code, or DNA.

   However, even if so, what would cause the information to be arranged in a particular manner? How does inert matter arrange itself? What causes the letters of the English alphabet to form words if left on their own? What causes DNA to arrange itself in a particular genetic sequence if it is merely a non-living molecule? Let alone a molecule which self-organizes and self-perpetuates.

5. Is it natural selection? Since when did natural selection act at the atomic level? How does natural selection act on subatomic particles?

6. Moreover, even if a few letters could, somehow, by chance, arrange themselves into words, and words into sentences, and sentences into paragraphs, and paragraphs into chapters, and chapters into a book, each subsequent step would seem to prove increasingly challenging. It's the old question of how long it takes for a monkey to type out the works of Shakespeare.

7. There may need to be new information at each subsequent step. A phrase like "In the beginning" may have arranged itself randomly, not to mention somehow well enough to convey meaning, but the sentence "In the beginning God created the heavens and the earth" contains more information. Namely "God created the heavens and the earth".

   Likewise it's one thing to have a single gene, but it's a lot more to have an entire genome. Let alone an entire organism.

   Hence a question which needs to be addressed is from where does this extra information come? Who or what is adding extra words or sentences or paragraphs into our book? Who or what is injecting additional information into each subsequent step?

   Otherwise is the information self-generated somehow, like an artificially intelligent computer writing new code for itself? How so? That seems highly implausible in the earliest lifeforms which surely would have not been anything like an A.I. computer.

8. Any time information is generated, there needs to be some way to check it for errors. Quality assurance. Yet could one physical entity (an error checking mechanism) have (more or less) co-evolved with another physical entity (e.g. a molecule like RNA or DNA)? How could a complex error-check have evolved roughly simultaneously with a presumably simple molecule in the origin of life?

Kenny on Noble

Anthony Kenny on Denis Noble:

When I was a bachelor don at Balliol I shared a staircase with Denis Noble, who was a physiology tutor: my rooms were on one side of the staircase and his on the other. We were both courting at the time, and so would also meet each other's fiancées on the stairs. We shared students as well as premises. There was an honour school called PPP: Psychology, Philosophy and Physiology. Denis taught the students physiology and I taught them philosophy. At meals in college we often discussed topics of common interest: Denis was not only a physiologist but as competent a philosopher as any of my colleagues.

In those days, there was a broad consensus that the sciences formed a hierarchy in which each level was to be explained in terms of the one below it: psychology was to be explained by physiology, physiology by chemistry, and chemistry by physics. This scientific strategy was called 'reductionism', since all sciences were ultimately to be reduced to physics. The idea was pithily expressed by Jim Watson, one of the discoverers of DNA: 'There are only molecules – everything else is sociology.'

Reductionist science chalked up victory after victory, as more and more lower-level mechanisms were discovered to explain higher-level processes. One such discovery was made in 1984 by the young Denis. He explained the pacemaker rhythm of the heart in terms of the flow of ions of potassium and calcium through protein channels. This achievement established his credentials as a reductionist biologist. However, he did not long continue to be a card-carrying member of the fraternity. He soon realized that in the heartbeat there was not only upward causation from the molecular level to the cellular level, but also downward causation from the cell influencing the molecules. Denis chaired the meeting at which I challenged Dawkins on the explanatory power of genes, and he took my side in the argument.

After I became Master of the college I ceased to share students with Denis, and so we had less opportunity for scientific discussion. However, our paths remained entwined at an administrative level. For two years, Denis served as my vice Master. This period included the year in which Mrs Thatcher was proposed, and then rejected, for an honorary Oxford degree. Denis was a founder of the Save British Science campaign which protested against the Thatcher government's cuts to the science budget, and he took a leading part in the campaign against the proposal. After the proposal was rejected, 200 alumni wrote separate letters to Balliol, either to applaud or to condemn the decision of Congregation. Denis and I divided between us the burden of replying. I, who had voted in Council in favour of the degree, wrote to the pro-Thatcher correspondents, while Denis wrote to the rest.

In retirement, I have been delighted to resume philosophical and scientific discussions with Denis. He has now come a long way from his reductionist beginnings. In his latest book, Dance to the Tune of Life, he enunciates a principle that he calls 'biological relativity'. This states that in biology there is no privileged level of causation: living organisms are multilevel open systems in which the behaviour at any level depends on higher and lower levels, and cannot be fully understood in isolation. Levels are distinguished from each other by their degree of complexity. If we start with atoms, we move upward through the levels of molecules, networks, organelles, cells, tissues, organs, whole-body systems and whole organisms.

One of the goals of reductionism was to eliminate from science all teleology or goal-directedness. In fact, Noble argues, teleology is ubiquitous in nature. However, it operates in different ways at different levels. At the purely molecular level, the protein-membrane network that sustains cardiac rhythm has no goal: its function only becomes clear at the level of cells. In its turn, the cellular activity serves a purpose that only emerges at the still higher level of the cardiovascular system.

While he remains a thoroughgoing Darwinist, Denis challenges the neo-Darwinism of Dawkins. He rejects the assumption that natural selection working on chance variations in genetic material is entirely sufficient to explain all evolutionary change, and has followed up the critique of The Selfish Gene that we began in his Holywell Manor drawing room years ago. In Dance to the Tune of Life, he argues that genes are not agents – selfish or unselfish: they are only templates – mere organs of the living cell:

There is nothing alive in the DNA molecule alone. If I could completely isolate a whole genome, put it in a Petri dish with as many nutrients as we may wish, I could keep it for 10,000 years and it would do absolutely nothing other than to slowly degrade.

Moreover, DNA is not sealed off from the outside world: it is subject to modification from within the organism and from the environment. Human beings and other animals are not lumbering robots but autonomous agents who can affect not only their environment but also the make-up of their own genome.

In 2017, Denis organized a joint conference between the Royal Society and the British Academy on the new trends in evolutionary biology. Despite attempts made to block it by outraged neo-Darwinists, the conference was well attended and excited all the participants. I am proud to have had a hand in the early stages of its organization. Its proceedings have recently been published by the Royal Society in its journal Interface Focus.

To this day, Denis and I continue our discussions on the relationship between philosophy and science. We both agree that the notion that science is necessarily and uniquely reductionist is not an empirical discovery, but a philosophical postulate. We both agree that teleology is undeniable and ubiquitous, but that we do not know, and perhaps cannot know, whether this is simply a fundamental feature of nature, or whether there is some supreme level at which it has an explanation. Certainly science cannot tell us whence the universe originated, and whether it has an ultimate goal. In his latest book, Denis suggests that even in asking these questions we have reached a boundary across which we cannot go.

(Brief Encounters: Notes from a Philosopher's Diary, pp 185-188.)

The zombie snail

Kinda like the relationship between Democrat politicians and voters who elect them:

https://www.wired.com/2014/09/absurd-creature-of-the-week-disco-worm/

Puppy love

Freewill theists typically say that true love must be "freely" given and "freely" received, meaning lover and beloved must both be able to withhold love. With that in mind, how many freewill theists are dog owners? Do they think their pet dogs express true love for their human family? Dogs descend from social animals (wolves). On top of that, dogs are bred to be even more beholden to humans. So both by nature and selective breeding, dogs have been programmed to bond with their human family. According to freewill theism, their psychological conditioning makes them furry robots or hairy puppets. 

Biological relativity

A paper (2011) from Denis Noble, a secular scientist who dissents from neo-Darwinism:

A theory of biological relativity: no privileged level of causation

Abstract

Must higher level biological processes always be derivable from lower level data and mechanisms, as assumed by the idea that an organism is completely defined by its genome? Or are higher level properties necessarily also causes of lower level behaviour, involving actions and interactions both ways? This article uses modelling of the heart, and its experimental basis, to show that downward causation is necessary and that this form of causation can be represented as the influences of initial and boundary conditions on the solutions of the differential equations used to represent the lower level processes. These insights are then generalized. A priori, there is no privileged level of causation. The relations between this form of ‘biological relativity’ and forms of relativity in physics are discussed. Biological relativity can be seen as an extension of the relativity principle by avoiding the assumption that there is a privileged scale at which biological functions are determined.

What Is Race? Four Philosophical Views

What Is Race?

Four Philosophical Views

Joshua Glasgow, Sally Haslanger, Chike Jeffers, and Quayshawn Spencer

Table of Contents

Introduction
Chapter 1: Tracing the Socio-Political Reality of Race, Sally Haslanger
Chapter 2: Cultural Constructionism, Chike Jeffers
Chapter 3: How to be a Biological Racial Realist, Quayshawn Spencer
Chapter 4: Is Race an Illusion or a (Very) Basic Reality? Joshua Glasgow
Chapter 5: Haslanger's Reply to Glasgow, Jeffers, and Spencer
Chapter 6: Jeffers' Reply to Glasgow, Haslanger, and Spencer
Chapter 7: Spencer's Reply to Glasgow, Haslanger and Jeffers
Chapter 8: Glasgow's Reply to Haslanger, Jeffers, and Spencer

https://global.oup.com/academic/product/what-is-race-9780190610180?cc=us&lang=en&

"Nazi" biology

https://www.youtube.com/watch?v=n5D_ltpw7CI

Questions of ultimate causation

Are we primates?

i) A prima facie evidence for human evolution is the fact that some apes/monkeys have a humanoid appearance. So it may seem like special pleading for Christians to deny the connection. 

ii) The comparison suffers from sample selection bias. For instance, baboons and mandrils look decidedly inhuman. 

iii) Gen 1-2 indicates that humans do have a basic affinity with the animal world. Up to a point, comparisons aren't contrary to Scripture. 

iv) However, comparative anatomy isn't the only way or best way to approach the issue. If God designed human beings to have the abilities that Scripture ascribes to human beings, could we have a fundamentally different body plan, or is this roughly the kind of body plan we have to have? 

v) Bipedalism frees up the hands. That enables us to have hands designed for manuel dexterity rather than locomotion or weaponry.  

vi) Forward-facing eyes are necessary for eye-hand coordination. They go together. 

vii) We have flat faces because our tongues, lips, dentation, &c., are designed for speech. A fringe benefit is kissing!

viii) By contrast, animals use their snouts to reach/grasp food. In humans, our hands replace that function. 

ix) In predators, the muzzle is a weapon. The jaws are serrated knives. But that's a quadruped design. In humans, we use hands and reason to make tools, shelter, weapons. 

x) Likewise, snouts enhance the sense of smell. In humans, by contrast, the visual sense is dominant. 

xi) Our flat, fairly hairless faces contribute to facial communication. We have expressive faces. A natural kind of sign language.  

xii) It's not clear to me how well a head with a muzzle and human-sized cranium is suited to an upright posture and bipedal locomotion. Flat-faces and bipedalism may be allometrically interrelated to facilitate stability and balance. Consider horror flicks with humanoid werewolves (e.g. The Howling, Dog Soldiers). They look pretty ungainly. 

xiii) Bipedal design facilitates a variety of sex positions. Face-to-face intercourse promotes emotional intimacy. 

xiv) Manual dexterity and hairless bodies enhance the sense of touch, which promotes social bonding (e.g. stroking, caressing, holding hands). Likewise, hairless bodies make wading, bathing, and swimming more enjoyable. 

xv) Upright posture and manual dexterity facilitate hugging, holding children, and riding piggyback–which promote social bonding. 

xvi) Hairless bodies make sense if we originated in a hot climate like the Middle East. 

xvii) Permanent breasts contribute to sex appeal, which promotes social bonding. 

In general, the human body plan is pretty much what we'd expect if the Biblical doctrine of man's special creation is true. If we originated in the Middle East. 

Philosophical contradictions in transgender worldview

http://www.thepublicdiscourse.com/2018/02/20971/

"Kristin" Beck

A retired Navy SEAL Team 6 hero who is transgender had a message for President Donald Trump after he announced the US military would bar transgender people from serving.

"Let's meet face to face and you tell me I'm not worthy," Kristin Beck, a 20-year veteran of the Navy SEALs, told Business Insider on Wednesday. "Transgender doesn't matter. Do your service."

Beck is not just your average service member. Born Christopher Beck, she served for 20 years in the Navy with SEAL Teams 1, 5, and, eventually, the elite 6. She deployed 13 times over two decades, including stints in Bosnia, Iraq, and Afghanistan. She received the Bronze Star award for valor and the Purple Heart for wounds suffered in combat.

http://www.businessinsider.com/kristin-beck-trump-transgender-ban-2017-7

i) To begin with, a "transgender woman" is a biological male. But the logic of trangenderism is that "transgender men" (i.e. biological females) should be able to serve in elite forces. However, the fact that a "transgender woman" (i.e.. biological male) can be an effective Navy SEAL hardly means a "transgender man" can pull it off. Men and women have dramatically different physical and psychological aptitudes. For instance:

http://www.nationalreview.com/article/423888/women-in-combat-marine-corps-study

ii) In addition, I assume Beck wasn't on hormone therapy during his time as a Navy SEAL. But if, to be a "transgender woman," he must undergo hormone therapy, that will impair his speed, strength, and stamina. He'll no longer perform at peak ability, compared to his normal, untransitioned self. 

By the same token, would Beck have been a successful Navy SEAL if his parents put him on puberty blockers during adolescence? 

Same problem with the Bruce Jenner comparison. Think "Caitlyn" could still win the decathlon if he underwent hormone therapy? Not to mention hormone blockers as an adolescent boy. 

"Being transgender doesn't affect anyone else"

Tell that to the biological girls and women who are now getting creamed in competitive sports by "transgender females". 

Creationist biology

http://toddcwood.blogspot.com/2017/06/igh-conference-monday.html

The origin of life

Jonathan McLatchie recently did a webinar with Intelligent design theorist and young-earth creationist Paul Nelson:

https://www.youtube.com/watch?v=K1b5kW-ioeo

Between about about the 1 hr 46 min mark until about 2 hr 18 min, Nelson had an impromptu debate with Darwinian biologist and militant atheist Zachary Moore.

i) I believe Moore's impediment is the assumption that direct causation is impossible. For X to cause Y, there must be an intervening physical medium.

That, however, exhumes the ancient conundrum of infinite divisibility. Take particle physics. You can keep down down lower scales of matter and energy, but if you insist that cause-effect transactions require an intervening medium, then there's no ultimate explanatory terminus, for there must always be some physical medium in-between the cause and effect to facilitate the transaction.

ii) Another one of Zach's impediments, which Nelson kept returning to, is Zach's failure to distinguish what constitutes a scientific explanation given an ongoing cyclical process from what constitutes a scientific explanation of how that cyclical process originated. The fact that we may commonly require identification of a natural "mechanism" given the existence of a cyclical process does not imply that such a demand is reasonable to account for the given itself.

iii) Zach also missed the point of Nelson's SETI illustration. The point is that we'd be justified in inferring that signals from outer space transmitting Pi are the product of an advanced alien civilization even if we didn't an inkling about the technology by which they were able to transmit a signal that distant. You don't require the identification of a mechanism before you're warranted in inferring design or intelligent agency.

"Animadversions of a Synthetic Chemist"

From James Tour:

Life requires carbohydrates, nucleic acids, lipids, and proteins. What is the chemistry behind their origin? Biologists seem to think that there are well-understood prebiotic molecular mechanisms for their synthesis. They have been grossly misinformed. And no wonder: few biologists have ever synthesized a complex molecule ab initio. If they need a molecule, they purchase molecular synthesis kits, which are, of course, designed by synthetic chemists, and which feature simplistic protocols.

Polysaccharides? Their origin?

The synthetic chemists do not have a pathway.

The biologists do not have a clue.

[...]

Those who think scientists understand the issues of prebiotic chemistry are wholly misinformed. Nobody understands them. Maybe one day we will. But that day is far from today. It would be far more helpful (and hopeful) to expose students to the massive gaps in our understanding. They may find a firmer—and possibly a radically different—scientific theory.

The basis upon which we as scientists are relying is so shaky that we must openly state the situation for what it is: it is a mystery.

Functional coherence

I appreciate Jonathan McLatchie's ministry Apologetics Academy including his interviews with various guests on various topics. Starting around the 35 minute mark, Doug Axe explains what he thinks is a limitation with Michael Behe's irreducible complexity and instead argues for what Axe terms functional coherence:

Self-hating atheism

In the pecking order of spokesmen for atheism, or secular philosophers in particular, Paul Draper is one of the better representatives. So this is a window into the mind of a prominent atheist thinker:

More importantly, if theism is true, then God is not only morally perfect, he is omnipotent and so could make many different sorts of intelligent life, probably infinitely many, including intelligent beings that are much more impressive than human beings. On single-universe naturalism, by contrast, one would expect that, if there is intelligent life, it will be relatively unimpressive. I want to emphasize the word "relatively" here, because I am not denying that human beings are impressive in many ways. But examined from the perspective of what is possible for an omnipotent being, we are, in terms of intelligence, a hair's breadth away from monkeys. Again, one would expect this on single-universe naturalism because the more intelligent the life, the less likely it is that naturalistic processes would produce it. Of course, if one believes in God and, looking around, finds nothing more impressive than human beings, one will be forced to conclude that God wanted to make beings with very limited intelligence. But surely one would not have predicted this beforehand. There are indefinitely many different kinds of creatures that an omnipotent being would have the power to create and that, other things being equal, would be more valuable to create than humans. Antecedently, a God would be more likely to create these more impressive creatures than to create us.
One might object, however, that a good God would not be obligated to create the best and that a loving God might very well want to create and love inferior beings like us, especially since that doesn't preclude his also creating other more impressive beings. I don't deny that a God might create beings like us--that is certainly possible. Similarly, Collins admits that fine-tuning is possible even if single-universe naturalism is true. The issue, however, is what is antecedently likely--what a reasonable person would expect beforehand. And human beings have many features that make them an unlikely choice, no matter how many other sorts of beings God creates. This is especially true, if we take the term "human" not merely in the biological sense but in a fuller sense that implies some of our most notable and notorious characteristics. In this sense of the term "human," the sense intended when someone says "I'm only human," being human implies being naturally selfish (not to mention territorial and aggressive), which greatly limits our potential for developing morally, especially given our limited life span. It also includes the fact that we are profoundly ignorant beings, especially when it comes to moral and religious matters, as is obvious from the fact that we disagree or are uncertain about many important moral and religious issues. We also naturally identify with others that we perceive to be like ourselves, leading, if not always to prejudice and intolerance, at least to isolation for those different from the norm. (I could go on and on, but it's too depressing.) 

http://infidels.org/library/modern/paul_draper/no-design.html

i) Draper is like a grown child who complains that his parents wronged him by conceiving him. He didn't consent to exist. He didn't give his parents permission to conceive him! Draper is a self-hating atheist. The existence of unimpressive humans like Draper is evidence that God doesn't exist. 

Of course, that's a bit of a paradox. If God made more impressive creatures instead of humans, then humans like Draper would be in no position to complain about how unimpressive they are, since they wouldn't exist in the first place.  

ii) Then there's the standard of comparison. Impressive to whom? Valuable to whom? Since any creature God made, however great, would be infinitely inferior to God's surpassing greatness, God can't be impressed by any creature. It's nonsensical to say a creature could be impressive in relation to God. 

Valuable to whom? Well, most humans value their own existence. Most humans value other humans. 

iii) Apparently, Draper means impressive relative to some hypothetically greater creature. Even so, why should God care about that? Since any creature will be unimpressive by God's standards, we're talking about a pecking order of unimpressive creatures, where, at best, one unimpressive creature is more unimpressive or less unimpressive than another. Hard to see how degrees of unimpressiveness would single out any candidate for existence. "Sure, I'm unimpressive, but you're even more unimpressive!"

iv) Draper's objection is equivocal. A creature can be more impressive in one or more respects than another creature, but less impressive in one or more respects. In some respects, many major predators are more impressive than humans, but they lack our intelligence. Likewise, many creatures have sensory aptitudes or acuities that we lack, but we're far smarter than they are. How disadvantages in one respect are offset by advantages in another respect is part of what makes animals interesting. Humans are very weak creatures compared to so many other animals, yet we're the dominant species. 

v) This also goes to the issue of tradeoffs. No one creature can combine every superlative excellence. Some abilities exclude other abilities. Take the ability to fly. 

Or consider the human brain. It's already so big that it makes childbirth difficult. Moreover, the size of the brain must be balanced out by other physical requirements, like blood supply. If we had larger lungs, we could run faster for longer, but that would require other compensatory adjustments. And so on and so forth.

Moreover, humans are a package. To do what we do requires a combination of brainpower, bipedalism to free up hands with fine-motor abilities, and front-facing eyes to coordinate eye-to-hand calibration. If we were quadrupeds, we'd be faster, but our superior intelligence would be frustrated by a body ill-suited to our intellectual abilities. 

vi) In addition, humans are earthlings. We share a planet with many other creatures. It would be incongruous to have a world in which one species is incomparably more impressive than all the others. 

vii) Draper's criterion is atomistic. The standard of impressiveness isn't simply individual organisms, considered in isolation, but the sheer variety of creative strategies on display. 

viii) Draper fails to distinguish between creation and the Fall. 

ix) Draper commits a common mistake with respect to omnipotence. If an omnipotent God uses natural means, then that limits what he can do. That doesn't mean he's limited to natural means. He can often bypass natural processes to produce a particular result directly (although even that's not true in the case of second-order effects), but if he's making physical organisms, if he's making a physical world in which things usually operate by a natural process of cause and effect, then that's a self-imposed restriction on his field of action. 

x) It's possible that our far-flung universe does contain more impressive creatures than humans. 

Neither fish nor fowl

So the Lord said, “I will blot out man whom I have created from the face of the land, man and animals and creeping things and birds of the heavens” (Gen 6:7).

A common objection to the flood account is that Noah's ark wasn't big enough to house all the animals, and even if it was big enough, eight passengers are hardly enough to care for them. A dilemma. 

That's not an issue for old-earthers, who espouse the local flood theory. From their standpoint, the ark only contained a representative sample of regional species. 

For young-earthers, it's more complicated. Of course, young-earthers have standard answers to standard objections. 

One issue concerns the scope of Gen 6:7. The wording seems to describe land animals. It's a shorthand for classifications in Gen 1, although it tellingly omits to include aquatic creatures. 

Whether insects were included is a tricky question. But let's skip that for now.

One question is where to draw the line between land animals and aquatic creatures. That's because we have borderline cases. In terms of their degree of adaptation to an aquatic or terrestrial environment, animals range along a continuum. A shark, dolphin, orca, and octopus (to name a few) is totally adapted to an aquatic environment. 

However, a sea krait is more adapted to an aquatic environment than a water moccasin or anaconda, but less adapted to an aquatic environment than a sea snake, while a horned viper is a land animal, although it can swim in a pinch (I assume). 

A seal or crocodile is more adapted to an aquatic environment than the beaver, otter, or hippopotamus, but less adapted than a shark, dolphin, orca, or octopus, while a mink or raccoon is less adapted to an aquatic environment than a beaver, otter, or hippopotamus, but better adapted than a marten. 

The tortoise is a land animal while a turtle is aquatic. Most crabs are aquatic, yet there are land crabs. Some frogs are primarily aquatic while other frogs are primarily terrestrial or even arboreal. 

For the young-earther, it's an interesting question which animals would be included or excluded from the ark when it comes to borderline cases. Of course, young-earthers deny a one-to-once correspondence between prediluvian and postdiluvian species. I'm using modern-day examples to illustrate a point. Presumably, there'd be prediluvian analogues (i.e. borderline cases).

Rather than a taxonomic distinction, a young-earther could draw a pragmatic distinction. Which animals made the cut would be a question of which animals could survive (or not) outside the ark. 

Are invertebrates living organisms?

This is a sequel to my earlier post:

http://triablogue.blogspot.com/2016/01/nephesh-chayyah.html

One argument I've run across to prove that invertebrates aren't "alive" in the Biblical sense is Lev 17:11 (cf. Gen 9:4; Deut 12:23), which says the "life of the flesh is in the blood." Since invertebrates don't have hemoglobin, they aren't living creatures in the Biblical sense. But there are several problems with this line of argument:

i) To say life is linked to blood is not to say life can't be linked to something other than blood. It's an affirmation, not a denial. It's perfectly consistent with other things on which life is dependent. Indeed, creationists hardly think blood is a sufficient condition for biological life.

There's no reason to think the statement involves an intended contrast between hemoglobin and hemolymph. The context concerns sacrificial land animals (or human murder victims). It's not meant to be a universal principle.

Take a statement like "life depends on water." That doesn't mean life only depends on water. It doesn't stand in contrast to "life depends on oxygen," or "life depends on sunshine."

Likewise, it's dubious to think the Pentateuch is using "blood" in the technical sense of hemoglobin, as if the concept depends on how modern medicine defines the composition of blood. That's terribly anachronistic.

ii) This interpretation would restrict Gen 1:20-21 to the creation of aquatic vertebrates, leaving the creation of aquatic invertebrates unaccounted for. But surely this passage is meant to be an inclusive statement about the creation of organisms for whom water is their natural element. Gen 1 subdivides creation according to their native habitat: air, land, water. And young-earth-creationists, of all people, should wish to affirm that Gen 1 was meant to cover, in broad categories, the creation of natural kinds on planet earth. To omit aquatic invertebrates would be a massive lacuna.

iii) What is the function of blood? It's a vital fluid. That's why blood loss can result in death.

But for invertebrates, hemolymph is functionally equivalent to hemoglobin. Both are vital fluids, without which the respective organisms will expire. Just as life is in the hemoglobin for vertebrates, life is in the hemolymph for (some) invertebrates.