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I am a politically-progressive, ethically-herbivorous anthropoid pursuing a paleontology education in the Los Angeles Basin. I am largely nocturnal, have rarely been photographed, and cannot thrive in captivity.

30 July 2011

Sorry, Archie; There's An Earlier Bird Getting Your Worm

Add this to the ever-growing list of things Darwin and Huxley might have been wrong about: Archaeopteryx wasn't a bird, after all! Or was it?

The bird-dinosaur link is perennially confusing to people, sometimes even to me. Cladistically speaking, birds are dinosaurs, literally. They never stopped being dinos, any more than humans stopped being primates. The debate here isn't whether Archeaopteryx was an early bird, but whether it was an avian or a non-avian dinosaur.

But, the zeitgeist, even among paleontologists, continues to demand that we think of animals in discrete categories (or "kinds," as creationists like to put it). This, in turn, leads to "missing link" quests that promise only to cloud rather than clarify public understanding.

The editors at Nature's press release office should know better than to frame the discovery this way. But, it's what gets headlines, so I can't really hold it against them.

Book Review: "The Animal Connection" By Pat Shipman

Such a wonderful read, and a much-needed demonstration of the folly of ignoring the obvious. Here's a book that looks at the culturally universal phenomenon of human cross-species emotional connection through the lens of evolutionary theory and asks, "how did this behavior arise? What selective benefit did it give early hominins to adopt members of other species into their own tribes and families?"

And it's no mushy cute-fest, either, let alone a sentimental appeal for us to love animals. Instead of saying we should love nonhumans, Shipman begins with the observation that we already do, and works from there. What may be the book's greatest failing from an ideological animal-liberation perspective -- Shipman draws no ethical conclusions from her observations, and mentions the movement only peripherally as one modern expression among many of an ancient human trait -- is probably its greatest strength as a work of popular science literature. It will hold its greatest appeal for average dog- and cat-lovers inclined to ponder their love for their pets from an evolutionary perspective, and steers scrupulously clear of any sort of animal advocacy. But that's no reason not to read it.

Shipman states her hypothesis clearly right from the start:
I believe that a defining trait of the human species has been a connection with animals that has intensified in importance since at least the onset of stone toolmaking 2.6 million years ago. Defining traits are what makes humans human, what makes us different from all other animals, and they are partially or wholly encoded in our genes. I don't claim that the animal connection is the only defining trait ... but I do claim that our connection to animals is so deep, so old and so fundamental that you really can't understand human evolution and nature without taking it into account.
Shipman contends that at each of the "big three" advances in human behavioral evolution -- toolmaking; language and symbolic behavior; and domestication of other species -- an ability to form empathic bonds with nonhuman animals played a crucial, if not determinative, role. From there she embarks from the beginning of human evolution and works her way up  to modern times, laying out her evidence at the three big shifts in an impressively comprehensive approach.

Obviously, I'm not going to list all her evidence here -- after all, this book is well worth reading in its entirety, and I'm certainly not going to make it easy for you to crib. But I will say that of all the "big three" shifts, I think her evidence for the animal connection's role in the spread of language and symbolic behavior is the weakest. Her argument on this point is both persuasive and parsimonious, but the direct evidence of it in the book is sparse. Nonetheless, as a whole the book is brilliant, rigorous, and at times even moving.

It's also one of the most scientifically-accurate popular explanations of human evolution that I've read in about 10 years.  That alone is worth the price of admission.

The book was moving and useful to me because it helped me make some evolutionary sense of my life-long feelings of empathy for animals, my veganism and my animal advocacy. I don't need to tell you any of the silly, hurtful things I've had strangers and loved ones say to me about my "unnatural" lack of species loyalty; I'm sure you've heard many of the same crude remarks yourself.

But if you're like me, you've always known that your sense of connection to nonhumans was a deep-seated, unchosen part of who you are. It has always felt like the most natural thing in the world to you, as much a part of your make-up  as your love for family or country. To you, as to me, these other animals have always felt like part of the tribe, and it was a mystery to you why other humans wouldn't agree.

Shipman argues that this is an expression of an ancient, and probably partially genetic, impulse in H. sapiens. Nature, she claims, has selected for cross-species empathy in hominins. In the early days, it was useful to our ancestors in acquiring animals for food and resources; hominins who understood animal thought and behavior were more successful than those who weren't. And nature intensified this trait as more hominins found more uses for it over millions of years.  But as with most inherited traits, the animal connection lends itself to more than one expression. And so, we now live in a world where people lavish pets with billions of dollars in consumer spending, identify tribally with animal-totem athletic teams or cartoon characters, continue to visit zoos and circuses even in economically-depressed times, and -- in one little corner over here -- agitate earnestly for the liberation of nonhumans from exploitation.

It's all, Shipman argues, perfectly natural, and all characteristically human. We all express the animal connection in different ways, but it's still there, almost everywhere you look in human culture and history.

There are no statements of animal advocacy in Shipman's book, but she has done the animal liberation movement a great service in writing it. She acknowledges as an empirical fact what we have always known, and often waste a great deal of wind trying to convince speciesists of -- that empathy for nonhuman animals is one of the most human things there is. It does not require any more intellectual justification than possessing vertebrae or walking upright. It's simply a given of human nature.

This is what I meant earlier when I mentioned "the folly of ignoring the obvious." We ignore the obvious connection between human and nonhuman every time we try to convince speciesists of its existence; or rather, we become complicit in and indulge their often-willful ignorance of the connection. Do we waste time trying to convince people that it's natural to breathe? Well, we shouldn't waste our time convincing them it's natural to care about animals, either. It wastes our time, and the animals' time, too... time that animals don't have.

By using the obviousness of the animal connection's existence as her starting point, Shipman has, whether she knows it or not, advanced the debate about animals by leaps and bounds, and helped ground animal liberation ethics in a evolutionary view of life... and moreso than any actual animal-lib thinker who comes readily to my mind. This is a book I'll return to time and again.

11 July 2011

Informing Our Ethics With Evolution

Let's face it, the implication of this blog's name is kind of cheeky. Despite my disclaimers, it still implies that there's a necessary connection between "paleo"-something and veganism. Maybe, if I had it to do over again, I'd call the blog "Evolvegan" instead, because that's closer to what I think I was driving at.

There's always been an insight floating around nebulously in my subconscious about what the study of evolution can say about animal liberation and ethical veganism. But until recently, I hadn't been able to put it in words. I left that, inadvertently, to someone else.

Someone I've exchanged a few emails with wrote a sentence that set off alarms and ignited light bulbs in my head. As soon as I read it, I thought, "Yes! Yes, that's it, exactly!" It was like my pesky camera finally snapped into focus after months of my fiddling ineffectually with it. The sentence was simple, elegant, and immediately clear to anyone who truly understands evolution:

Suffering is conserved in all vertebrates.

That's the foundational insight of this blog, boiled down to bare essentials (thanks, D, for saying it so beautifully; I hope you don't mind my borrowing it). The only thing I'd add to it is:

And so is empathy.

These two emotions -- empathy and suffering -- exist in all vertebrate animals. If they didn't, there's no way they'd exist in humans. We inherited our capacities for empathy and suffering from a long line of common ancestors, as Darwin hinted at in both The Descent of Man and The Expression of Emotions in Man and Animals. Work since Darwin has only confirmed and expanded this insight.

It shouldn't surprise us, really. It should be obvious. But to a lot of people clinging to the specialness of their humanity, it's not obvious at all (speciesism is probably an inherited trait, too!). In fact, a lot of people expend their energy and bandwidth justifying their speciesism by appealing to evolution, accusing ethical vegans of not "getting it." They imply there's something un-natural about our advocacy.

But there isn't. Empathy and suffering are both conserved in vertebrates. When we act upon those two traits and seek animal liberation, we are grounded in our evolutionary kinship with other species.  We have taken the fact of common descent to its fullest ethical conclusion. Others may have different interpretations of the evidence, but that does not make their interpretation any more "natural" than ours.

It is perfectly natural to feel another being's pain, and to desire an end to their suffering. It's also natural to act on those feelings, and build an ethic around them. Attaching a "paleo" to the "vegan" is simply a proclamation of this kinship-by-common-descent.

We will not exploit, enslave or eat our kin.

Oh, and what about invertebrates? Do they suffer, too? Honestly, I'm not sure, but it costs me nothing to give them the benefit of the doubt. So, I won't eat them, either.

04 July 2011

Quite A Stretch, Mr. Darwin: Adaptation, Diet and the Giraffe's Short Neck

In studying evolution, the answer to any given puzzle is rarely obvious, even when we think it is.

Take the giraffe's long neck. This one seems like a no-brainer: giraffes evolved long necks in response to food scarcity and competition with other browsing mammals. Having a slightly longer neck enabled the giraffe's ancestors to reach slightly higher browse than other mammals, and over millions of years, the trait was inherited and enhanced by natural selection, producing the majestic, iconic animal we see today.

Or so you were probably taught. Just like me.  It  makes perfect, logical sense; intuitively, it feels right. Darwin himself made the same speculation in the sixth edition of On The Origin Of Species:
So under nature with the nascent giraffe, the individuals which were the highest browsers and were able during dearths to reach even an inch or two above the others, will often have been preserved; for they will have roamed over the whole country in search of food. That the individuals of the same species often differ slightly in the relative lengths of all their parts may be seen in many works of natural history, in which careful measurements are given. These slight proportional differences, due to the laws of growth and variation, are not of the slightest use or importance to most species. But it will have been otherwise with the nascent giraffe, considering its probable habits of life; for those individuals which had some one part or several parts of their bodies rather more elongated than usual, would generally have survived. These will have intercrossed and left offspring, either inheriting the same bodily peculiarities, or with a tendency to vary again in the same manner; whilst the individuals, less favoured in the same respects, will have been the most liable to perish.
Darwin's endorsement of this speculation has given it the force of orthodoxy, and this interpretation remains, 150 years later, the textbook example of a straightforward case of natural selection in action.

But it might be completely wrong.

I started thinking about giraffes after my interview at Let Them Eat Meat, in which I pointed out that evolution is more complex than most people realize, and therefore we should be wary of seemingly straightforward connections between food and (assumed) adaptations. What seems like a no-brainer might, on closer inspection, turn out to be a just-so story. As Stephen Jay Gould warned (in his classic essay The Tallest Tale, among many other places) "consequences of substantial import often arise from trivial triggers of entirely different intent. In other words, current utility bears no necessary relationship with historical origin."

In short, at the time of Darwin's writing, and even up to the time of Gould's, there was no body of evidence straightforwardly indicating that giraffes evolved long necks in response to dietary selection pressures. And despite the fact that there's been some excellent giraffe research done since then, there still isn't. The origin of the giraffe's long neck is still an intriguing mystery.

What makes a giraffe? 
If you're like most people (and why wouldn't you be?), you're accustomed to defining giraffes by their long necks. It's pretty much their distinctive characteristic in the common imagination. But it turns out that in this case (as in so many others), the common imagination is wrong. Most giraffes throughout Earth history have not had long necks. For that matter, giraffes today don't have long necks, either.

A giraffe struggles against its short neck to get a drink.
Yes, you read that correctly. Giraffes don't actually have long necks!

Just look at the stance they have to assume in order to drink water:  legs splayed, forming a triangle with the plane of the ground, stretching their necks to the water's surface... and then still barely able to reach.

Contrast this stance with that of any other terrestrial quadraped; say, the antelope, or the rhino. None of them have to stretch their legs in an awkward angle to take a sip. They just stroll up to the water's edge, bend their necks down, and drink. Their legs are never involved.

Not so with the poor giraffes, for whom every drink involves a yoga stretch. They may be the tallest land animals in the world, and their necks may be the longest among all others in absolute terms, but relative to their ability to get water, giraffes have shorter necks than any of their relatives among the ungulates, and arguably among any other group of terrestrial animals.

So upon closer inspection, it doesn't make much sense to define giraffes as a species based on their supposedly long necks. To figure out what makes a giraffe a giraffe, we have to look more precisely at their morphology and fossil record. What do modern giraffes, Giraffa camelopardalis, have in common with their closest living relatives, Okapia johnstoni? And what trait(s) do these two extant clades of giraffids share with their common ancestors and fossil relatives? What distinct anatomical feature(s) unites the living and extinct giraffids into a coherent taxon?

Okapi: the other giraffe! No long neck here, either...
As you've probably guessed by now, it's not long necks. The giraffid party is all about teeth; specifically, canine teeth. The diagnostic character of giraffid fossils -- that is, the derived trait paleontologists use to tell whether they've found a giraffid fossil or that of some other hoofed beastie -- is bilobed lower canine teeth, which are especially useful for stripping foliage off of browse.

This distinct trait first appears in the fossil record between 10 to 15 million years ago, with the rise of the Climacocerids, of whom the most famous member is the early giraffoid Canthumeryx syrtensis, who looked more like an antelope with horns askew than like what most people think of when they think "giraffe." C. syrtensis was a grazer/browser who lived in the lush flood plain/savannah/river basin habitat of what is now Libya, and had relatives all over North Africa and southern Eurasia, as far east as India.

In addition to being a relative of modern giraffes, C. syrtensis was likely also an ancestor of the sivatheres, a clade of bulky, moose-like giraffids who didn't have "long" anything, as far as we can tell.

Canthumeryx syrtensis
But the first animal with all the traits of a possible direct ancestor of modern giraffes, that also occupies the right geological position, is Giraffokeryx ("giraffe herald") from the Miocene Siwalik deposits of India/Pakistan. The Giraffokeryx looked more like an okapi than a modern giraffe, except that it had four ossicones rather than the two found in extant species.

Giraffokeryx is considered transitional between the canthumerycids and later giraffe relatives, and after it, things start looking a bit more familiar; its ancestors, the palaeotragines (who looked even more like the okapi than Giraffokeryx did), gave rise to the samotheres, who ultimately became the modern giraffe. The resemblance between okapi and basal palaeotragines is so strong that some have argued that the okapi is a "living fossil" representing the morphology of ancestral giraffids, unchanged over millions of years because it occupies a forest niche unchallenged by any other species.
Giraffokeryx

The samotheres replaced most of the other palaeotragines by the Miocene/Pliocene transition (9 to 5 Ma), and were generally larger and longer-faced than their ancestors, looking more and more like modern giraffes as time progressed. It was with this group that the elongation of the neck and legs really began to take off, and the genus Giraffa (which once contained six species, and now only one) was born between 7.1 to 7.3 Ma.

So, Why The Long Neck, Mr. Giraffe?
Fascinating as this evolutionary history is, though,  it still begs the question, "why did giraffes evolve long necks?"

But in a very real sense, that's the wrong question to be asking, let alone begging, since it's clear that most giraffes through time didn't have long necks, and relative to their own bodies, modern giraffes arguably don't actually have long necks, either. The real question, then, is, "what made Giraffa species get so much taller overall than their ancestors?" To make anything like an educated guess on that question, we have to look at the world in which giraffes emerged.
Sivatherium

The emergence of "true" giraffes across the Old World and their subsequent retreat into Africa happened against the backdrop of the Miocene/Pliocene transition, a time of enormous climatic, geographic and tectonic change. Starting about 10 Ma, the Himalayas and the Tibetan plateau entered a second phase of uplift and the Paratethys Sea began to slowly dry up and retreat. At the same time, other geologic processes like sea-floor spreading, silicate weathering and sediment burial began to lower atmospheric CO2 concentrations.

All of these factors working in concert fundamentally altered the ecology of central Asia and north Africa, (heck, the rest of the world, too), where Giraffa's ancestors had thrived. The region stretching from western India to northern and eastern Africa went from a tropical rainforest environment dominated by C3 plants to an arid savannah populated by C4 grasses. Deciduous forest biomes gave way to conifers and other small-leafed, arid-adapted plants. Rainfall became more seasonal north of the Himalayas, the Tibetan plateau became drier, and summer and winter monsoons got stronger. South of the Himalayas, summer temperatures and rainfall increased dramatically. Collision of the African and Eurasian tectonic plates caused coastal upwelling of the Arabian Sea and created land bridges between Europe, Asia and Africa, allowing for the migration of giraffids (and other species) into Africa. By 6 Ma, C4 plants dominated central Asia, and the decline of giraffids there began in earnest. Then, between 6 Ma and 2.6 Ma (the Plio-Pleistocene transition), there was further uplift of the Himalayas (throwing monsoonal patterns further out of whack), an expansion of continental ice-sheets, and a prolonged period of global cooling. These factors led to the extinction of Giraffa species in Asia, and the retreat of remaining giraffids into Africa.

It seems likely that these upheavals served as the crucible in which Giraffa developed its incredible suite of adaptations, including its height, but nailing down precisely which of these factors caused which of the giraffe's traits is tricky, if not impossible. In particular, the intuitively-appealing idea that height provided giraffes with a selective advantage over other herbivores becomes murkier upon close inspection.
Palaeotragus primaevus

The first giraffe researcher to raise an objection to this idea was Chapman Pincher, who made the following points in a 1949 Nature article titled "Evolution of the giraffe":

  • any dearth of resources that was long enough, severe enough and/or frequent enough to produce a selective pressure for long necks would cause a recurring wastage of young giraffes, and thus the extinction of the species; i.e., if young giraffes can't reach the high browse for which they're supposedly adapted until they reach adulthood, then they'll never reach adulthood!;
  • the same dearths would have produced selection for long necks in other herbivores, yet only giraffes achieved this adaptation; and,
  • adult male giraffes are, on average, one meter taller than adult females, who are in turn taller than all their young. Thus, dearths would place shorter members of the species at a permanent disadvantage, yet again ensuring extinction of the species.
Against these points, Pincher argued that the neck of the giraffe was only "long" because as their leg length increased, giraffes would need to be able to reach water sources from greater heights. Thus, their neck is just long enough to do the job, and no longer (remember their short necks?).

About 15 years later, A. Brownlee, also in a Nature article entitled "Evolution of the giraffe," agreed with Pincher's objections, but argued that height provided giraffes with improved thermoregulation and a better ability to avoid, detect and fend off predators.

The question of whether height provides a feeding advantage to giraffes is further complicated by the variant feeding patterns of giraffes in different habitats. In South Africa's Kruger National Park, for instance, male giraffes tend to feed at a greater height than females, who in turn feed at a higher level than young. Average feeding height is between 1.7 and 3.7 m, again with males tending to feed higher. This places female and young Kruger Park giraffes in direct competition with kudus, whose feeding height range is between 1 and 2 m. 

But in Kenya's Tsavo National Park, giraffes spend about 50 percent of their feeding time browsing below a height of 2 m. And in the Serengeti, they mostly feed on low-growing Grewia bushes.

On balance, then, it appears that, at least in Kruger Park, height provides giraffes with only a marginal feeding advantage. A marginal advantage is certainly good enough for natural selection to work with, but it doesn't explain why giraffes grow to an average height of 5 m when an average feeding height of 3 m would be all that's needed.

Yet another team of giraffe researchers argued that long necks are driven by sexual advantage rather than feeding advantage. Male giraffes frequently use their necks as weapons in defense of females in estrus, as well as in dominance contests with other males. Thus, there would be sexual selection for long necks in males, and female offspring would inherit the trait without really "needing" it.

But then, here we are again (potentially) indulging the adaptationist fallacy that current use is necessarily related to evolutionary origin. It might be that giraffe height has nothing to do with any of these clear adaptive advantages. Or, it might be the product of all of them at the same time. As Darwin noted, "(t)he preservation of each species can rarely be determined by any one advantage, but by the union of all, great and small." Or, it could be a side-effect of pleiotropy.

The bottom line is, we just don't know for sure why giraffes evolved to be so tall. And it'll probably stay that way for a long time. Until it's figured out, we should avoid the temptation to take at their word anyone speaking authoritatively about the importance of specific traits... even Charles Darwin. Truth is, in such situations, they're claiming to know more than they possibly could.

References:
  • Brownlee, A. 1963. Evolution of the giraffe. Nature 200: 1022.
  • Du Toit, J.T. 1990. Feeding-height stratification among African browsing ruminants. African Journal of Ecology 28: 55–61.
  • Leuthold, B.M. & Leuthold, W. Food habits of giraffe in Tsavo National Park, Kenya. East African Wildlife Journal 10: 129–141.
  • Mitchell G, Skinner JD: On the origin, evolution and phylogeny of giraffes Giraffa camelopardalisTrans Roy Soc S Afr 2003, 58:51-73. OpenURL
  • Pellew, R.A. 1983a. The giraffe and its food resource in the Serengeti. I. Composition, biomass and production of available browse. African Journal of Ecology 21:241-267. 2. Response of the giraffe population to changes in the food supply. African Journal of Ecology 21:269–283.
  • Pincher, C. 1949. Evolution of the giraffe. Nature 164 (4157): 29–30.
  • Simmons, R.E. & Altwegg, R. 2010. Necks-for-sex or competing browsers? A critique of ideas on the  evolution of giraffe. Journal of Zoology 282: 6-12.
  • Simmons, R.E. & Scheepers, L. 1996. Winning by a neck: sexual selection in the evolution of giraffe. The American Naturalist 148(5): 771–786.