Evolution

Evolution

Sverker [email protected] http://home.hj.se/~lsj/

School of Education & Communication

Högskolan i Jönköping

“Nothing in biology makes sense except in the light of

evolution”

Theodosius Dobzhansky

What is evolution?

Several closely related, but distinct, concepts:1. The historical fact that life on Earth has evolved and

changed over geological time2. Microevolution – small genetic changes from

generation to generation, observable both in nature and in the laboratory

3. Evolutionary theory – explanations for how evolution happens, and which processes and causal factors are involved

4. Macroevolution – combination of theory (3), experiment (2) and fossil patterns (1), to explain evolutionary history and the major transitions in evolution

Basic principles of evolution

Postulate that:

1. A set of entities exist, not all identical.2. These entities vary in their fecundity and/or longevity.3. The differences in reproduction and longevity are not

totally random, but are correlated with other features of the individual entities.

4. These different features are to some extent inherited in reproduction, so that there is a correlation between features of parent and offspring.

These postulates lead to Darwinian evolution!

• Entities with “good” features (giving long life and lots of offspring) will produce more than their share of the next generation.

• For each generation, a larger and larger fraction will be descendants of parents with “good” features, and will have inherited some of those features. The frequency of “good” features will increase in the population.

• Given enough time, the “best” features, giving maximum reproduction, will dominate the population.

Nota Bene: “good” means only good at surviving and reproducing, not “good” in any more general normative sense.

Problem: This process would seem to run out of steam after a while, when only descendants of the best remain, all identical.

Solution 1: The environment need not be constant. What’s “best” may change over time.

Solution 2: Other entities are part of the environment. Competion, “arms races”, and other forms of coevolution provides variation in what’s “best”.

Solution 3: New variation is generated -- mutations.

Furthermore…

• New variations generated no limit to how far the process may lead.

• Different environment in different locations evolution can go in different directions among different populations what used to be a coherent population may split up into several.

”Survival of the fittest”

• Literal struggle for existence, killing off competition – rare!

• Being better att getting food or otherwise more ”economically” efficient

• Being able to exploit new sources of food

• Being better at not becoming food

… so far it’s all about your own survival…

…but at least as important is reproduction…

How to make sure your genes are well represented in the next generation?

• Being attractive for the opposite sex• Driving off competitors of the same sex• Offspring quantity or quality?

– Get lots and lots of kids, and maybe a few will survive– Get a few kids, but protect them and provide for them so they

get a good start in life and give you many grandkids

Best way to spread your genes need not be total egoism

• Cooperating in a group can benefit every member (herd animals, multicellularity)

• Parents support their kids, that’s where the parental genes are being passed on...

• … but it can also be evolutionarily profitable to help sibling and other relatives -- they carry copies of your genes too!

• Cooperation between different species for mutual benefit (symbiosis) very common.

Limitations and misunderstandings 1

• Evolution does not plan ahead. Only features that are good here-and-now are favored.

• Very common that features change function, or acquire added functions. Circumvents problem with “useless” early stages.

• Evolution can easily get stuck in local optima, solutions that are good enough but not perfect.

• Evolution doesn’t care about “the good of the species” or “harmony of nature” or any other “higher” goal. The only thing that matters is which genes are spread most widely.

• Evolution, like any other science, has absolutely nothing to say about right and wrong in any moral sense. “Survival of the fittest” does not mean that the fittest has a better right to survive, just that the fittest as a matter of fact does more often survive.

Limitations and misunderstandings 2

• Evolution does not repeat itself. Only superficial similarities between different solutions to same problem. Corollary: same feature in two related species same features existed in common ancestor.

• Evolution is not about climbing up a ladder towards a goal.– No such thing as “up” and “down” in any general sense, no

“higher” or “lower” animals.– Family tree branching all the time, more bush than ladder.– Evolution does not have a goal in mind, does not look

forward, and never reaches a finish line.

How do we know that evolution is behind the diversity of life?

Evolutionary theory predicts patterns in nature:

1. All species, living fossil, should be connected in a single family tree

a) Newly discovered fossils should fit in the tree, occur at the right time and not connect distant branches

b) Different ways of making family trees should agree:i. Anatomy of living species

ii. Embryology

iii. Fossil evolutionary chains

iv. DNA

2. More embryologi: Features that are supposed to have a common origin should have a common embryology

3. ”Fossil features” in living species should be common, remains of ancestral structures no longer in use (hipbones in snakes & whales, tooth

genes in chicken, vitamin-C-gene in humans)4. Biogeography: geographic occurrence of

ancestors and descendants should make sense together.

5. ”Cul-de-sac” evolution, organs that are OK but not perfect, and no easy way out. (Human

retina & childbirth & spine & …)

Evolution of more than just the body

• The evolution of beavers is as much about dams as about teeth and fur!

• A beaver who builds better dams is more fit, and can ”win” the evolutionary race.

• How about humans who build better dams?

What evolves in language evolution?

• Biological adaptations of the human body for language use is certainly part of the story, but absolutely not the whole story.

Many parallel interacting processes:

• Biological exaptations (recycling of features that evolved for other purposes than language)

• Evolutionary processes in ontogeny

• Evolution of human social and cultural systems

and last but not least

• Evolution of language itself, as a cultural entity

Cultural evolution

• Our thoughts and concepts and ideas live inside our heads, and reproduce by spreading from person to person.

• Some ideas spread more easily than others.

• Ideas that spread more easily become more and more common among people.

• This looks a lot like Darwinian evolution!

• How much can be made of this analogy between ideas and animals?

Can evolutionary thinking be a fruitful tool in the study of languge

origins and language change?

• On one hand:– Hard to pin down the relevant entities that evolve,

and what features they have.– Easy to over-extend and abuse biological analogies,

something that has happened repeatedly in the history of the field.

– Many of the assumptions behind biological evolution of dubious validity in cultural contexts.

• On the other hand:– Language more thoroughly analysed and better

understood than other cultural and social system.– Many of the objections against cultural evolution do not

fully apply to language:• Concepts not well defined• Weak inheritance, low fidelity• “Mutations” under conscious control• Acquired features can be inherited (Lamarckian evolution)• Reticulate evolution, mixing features from different ancestral lines

Evolutionary thinking may well be fruitful in linguistics, but care is

needed.

Biological creatures versus linguistic “creatures”

• Genes, individuals, groups, species … and a lot of other biological concepts– are well-defined in most biological concepts– are the basis of biological theory – are needed for using the well-developed analytical

toolbox of evolutionary biology

• Corresponding linguistic concepts, if they can be identified, operationalised, and applied, will open the biological toolbox for the linguist

Gene-level

• The smallest unit that behaves as a coherent unit in transmission and reproduction

• The smallest unit that can carry a feature

• Possible linguistic equivalents: all those linguistic concepts that end in -eme:– Morpheme– Phoneme– etc…

and also– Grammatical rules and parameters– Phrases and fixed expressions

Replicator – Interactor

• Genes are copied in reproduction, but do not interact with the world directly. It is not the genes as such that succed or fail in the struggle for the existence.

• What directly interacts with the world is a system, an entity build by a set of genes to meet the world, an interactor..

• In biology, the interactor is normally an individual organism.

• Which linguistic entity interacts with the world as a coherent system in this manner?

Organism level

• The level that directly interacts with the world: – With other linguistic organisms– With people– With other relevant systems

• The lowest level at which all parts of language work together as a coherent system:

• The level at which language normally reproduces:

• The idiolect of an individual language user corresponds most closely to this description.

Species level

What is a species?• From an individual perspective:

A set of individual who can reproduce with each other.

• From a gene perspective: A gene pool within which genes spread freely.

• From a family tree perspective:An isolated branch in the family tree, separate from other branches.

• From each of these perspectives, it is clear that the linguistic equivalent of a species has to be something close to what we normally call a language, like Swedish, English, Japanese, or Cebuano

• Two idiolects belong to the same language, if a kid growing up hearing both does not become bilingual but integrates both into a single native language.

What can the different levels be used for?

1) Genes

• Gene level:– Useful for studies of linguistic “microevolution”, diachronic

language change– Possibly useful for studies of the interaction between

language features, and features of language learners, e.g. learning biases.

– Less useful for language origins, or for more general studies of the interaction with other evolving systems.

What can the different levels be used for?

2) Species

• Species level:– Useful for the study of language phylogeny, the historical

evolution of language families– Possibly useful for studies of bilingualism– Less useful for language origins, or for more general

studies of the interaction with other evolving systems.

Vad kan de olika nivåerna användas till?

2) Organisms:

• Organism level:– Alternative perspective on language: symbiosis between a

human and a linguistic organism– Theoretical analyses of symbiotic relations in biology can

be used.– Language acquisition – is it a kid acquiring a language, or

is it a language acquiring a new host? Same process, two perspectives may yield fresh insights.

– Coevolution between languages and their human hosts – who is adapting to whom? What impact does this have in the innateness debate?

– The human brain as an ecosystem, inhabited by both linguistic organisms and other cultural critters.

Conclusions

• Regarding humans and language as host and symbiont may provide fresh perspective on a variety of linguistic phenomena.

• Theoretical work from evolutionary biology may be applicable to some linguistic problems, and can generate predictions to test the host-symbiont perspective

• Linguistics is not biology. Analogies have limits, and must be handled with care.