Natural Selection and Adaptation

#1 Resources in an environment tend to be limited

#2 All species are capable of producing more offspring than can be supported by their environment

INFERENCE: Individuals in a population compete for survival. Only a small fraction of all organisms survive each generation.

#3 Individuals in populations vary

#4 Variation is heritable

INFERENCE: Survival in the struggle for existence is not random, but depends on the genetic constitution of the individuals. Those individuals who inherited those traits that best fit them to their environment are more likely to leave offspring in the next generation

INFERENCE: This unequal ability of individuals to survive and reproduce will lead to gradual changes in the population, with favorable characteristics accumulating over generations.

1 HOMO HABILIS ~ NICKNAME: Handyman LIVED: 2.4 to 1.6 million years ago HABITAT: Tropical Africa DIET: Omnivorous – nuts, seeds, tubers, fruits, some meat2 HOMO SAPIEN ~ NICKNAME: Human LIVED: 200,000 years ago to present HABITAT: All DIET: Omnivorous - meat, vegetables, tubers, nuts, pizza, sushi3 HOMO FLORESIENSIS ~ NICKNAME: Hobbit LIVED: 95,000 to 13,000 years ago HABITAT: Flores, Indonesia (tropical) DIET: Omnivorous - meat included pygmy stegodon, giant rat4 HOMO ERECTUS ~ NICKNAME: Erectus LIVED: 1.8 million years to 100,000 years ago HABITAT: Tropical to temperate - Africa, Asia, Europe DIET: Omnivorous - meat, tubers, fruits, nuts5 PARANTHROPUS BOISEI ~ NICKNAME: Nutcracker man LIVED: 2.3 to 1.4 million years ago HABITAT: Tropical Africa DIET: Omnivorous - nuts, seeds, leaves, tubers, fruits, maybe some meat6 HOMO HEIDELBERGENSIS ~ NICKNAME: Goliath LIVED: 700,000 to 300,000 years ago HABITAT: Temperate and tropical, Africa and Europe DIET: Omnivorous - meat, vegetables, tubers, nuts7 HOMO NEANDERTHALENSIS ~ NICKNAME: Neanderthal LIVED: 250,000 to 30,000 years ago HABITAT: Europe and Western Asia DIET: Relied heavily on meat, such as bison, deer and musk ox

Illustration: Ivan Allen

Who are we, anyways?

• Kingdom-animalia

– Phylum—chordata

• Class—mammalia

– Order—primate

» Suborder—anthropoidea

--Family—hominidae

--genus—homo

--species—sapiens

Chimpanzees (our closest relative) is family Pongidae, although some researchers believe chimpanzees and humans should be in the same family and genus

A broad picture of our family tree

A look at our family tree

Once We Were Not Alone

Paranthropus (Australopithicus) boisei, Homo rudolfensis, Homo habilis and Homo ergaster foraged in the same area around Lake Turkana.

From “Once We Were Not Alone” by Ian Tattersall in Scientific American 2003

Human Skull evolution

Some distinguishing physical characteristics of humans

Skull Features:

• Flat face

• Prominent Chin

• Modified teeth

• Large brain case (~1300 cc)—early hominids/chimpanzees ~450 cc

• Reduced brow ridges

• Smaller cheek bones

Other skeletal features

• Adapted for bipedal locomotion—changes in pelvis, foot

A Tour Through 7 Million Years of Human Evolution

No clear fossil evidence of last common ancestor between the line that would lead to chimps and the line that would lead to modern humans has been found yet

However, many other intermediates have been found.....

African Ancestors

Sahelanthropus chadensis: About 7 million years old, status as human ancestor unclear

Ardipithecus: 4.4 million years ago

Australopithecus afarensis: 3.5 million years ago

Homo habilis:2.4 million years ago

First clear use of stone tools

Homo erectus: 1.8 millionyears ago

Relationship between modern humans, Neandertals, and Denisova

Neandertal modern human

Neandertals:

350,000 to 30,000 bp

Gibraltar Child: A Neandertal Child

Modern humans: ~200,000 years ago

What else have we learned from the Neandertal genome?

1. People from Eurasia share 1-4% of their genomic variations with Neandertals:

“It may not sound like a lot -- between 1 and 4 percent. But that's the equivalent of one great-great-great grandparent's DNA contribution. In the case of the Neandertal contribution, more than 1500 generations ago, it's an enduring legacy of an ancient group of people, spread across many lines of the genealogies of living people.”--from John Hawk's (Associate Professor of Anthropology, U. of Wisconsin) weblog, May 6, 2010

2. Comparison of the modern human genome with the neandertal genome suggests that many human genes have been positively selected (relative to Neandertals) at 212 sites

--genes involved in metabolism, neuronal and skeletal functions

3. So far, only 88 single amino acid changes have been found between the protein sets of modern humans and Neandertals

Various scenarios explaining presence of neandertal genomic traits in modern humans

Evolution in tool making

Homo habilis (Oldowan stone tool industry)

Stone tools from Dmanisi site and insitu fossil

Early Homo georgicus (transitionBetween Homo habilis and Homo erectus)

Homo erectus

Trends in Brain Evolution

http://www.colorado.edu/intphys/Class/IPHY3730/05cns.html

Human Brain evolution

Recent Human Brain Evolution

Absolute Increase in brain volume

http://cas.bellarmine.edu/tietjen/Laboratories/Bio%20Pix%204%20U/Bio%20Pix.htm

Brain evolution trends (brain mass to body mass ratio)

Virtual endocasts (red) and crania (transparent) of four hominid taxa in comparison to visualize the differences in shape and relative position.

Comparative cranial configuration of monkeys, chimpanzees, and man. A: Monkey B: Chimpanzee and C: Man

Comparison of the Taung child endocast with apes and man. A. Frontal lobe of an ape. B. Taung specimen (A. africanus). C. Frontal lobe of a human. The simplicity and what seems to show sulcal pattern shows that the Taung resembles the chimpanzee.

Human and chimpanzee brains

Bradbury, molecular insights into human brain evolution, PLOS Biology (2005), Volume 3, Issue 3, 367

The variations between human and bonobo brains

Three-dimensional reconstruction of a reference bonobo (pygmy chimpanzee) brain (A) and a reference human brain (B) after magnetic resonance imaging and normalisation of absolute brain sizes. The virtual bonobo brain has been transformed into the virtual human brain using an elastic deformation algorithm. The local deformation vectors are colour-coded and projected onto the virtual human brain (C). The most dramatic changes in brain shape occur in (1) the ventro-orbital prefrontal cortex, (2) the ventral stream of the visual cortex, and (3) the hypothalamic neuroendocrine region.

Bradbury, molecular insights into human brain evolution, PLOS Biology (2005), Volume 3, Issue 3, 367

Why the increase in brain size?

• Consumption of meat

• Cooking

• Development of hunting

• Development of proto-language

• Increased social ability (cooperative living)

• Sexual selection

• General use (tool construction an use improvement helps over-all survival—may require bigger brains)

Genes involved in brain evolution?

• Microcephalin—mutations result in small brain size

– Certain mutations found in about 70% of humans arrived in the human genome about 37,000 years ago

• ASPM—mutations result in small brain size

Protein involved in spindle-formation (used during mitosis), so perhaps controls neuron division rate

Certain variants found in a quarter of people, arose around 5800 years ago

• Nde1—mutations result in premature neuron differentiation (in other words, less neurons and smaller brains—in mice)

• Glutamate dehydrogenase

Bradbury, molecular insights into human brain evolution, PLOS Biology (2005), Volume 3, Issue 3, 367

Evans et al., Science 9 September 2005: Vol. 309. no. 5741, pp. 1717 - 1720

Distribution of the haplogroup D variant of Microcephalin

Introgression of Microcephalin Haplogroup D into modern human populations

From Evans et al, http://www.pnas.orgcgidoi10.1073pnas.0606966103

Neandertals

Modern hum

ans out of A

frica

37,000 years

Questions about our genetic heritage that ancient DNA can help answer

• How are modern humans (Homo sapiens) related to Neanderthals (Homo neanderthalensis)?

– While it is unlikely that modern human evolved directly from Neanderthals, was there any interbreeding between modern humans and Neandertals?

– Has the Neanderthal genome made any contribution to the genome of modern humans?

Noonan et al. suggest that the original Homo sapiens/Neandertal split took place 706,000 years ago

and there was no genetic mixing after that time

Noonan et al , Science 314, 1113 (2006)

http://www.mnh.si.edu/anthro/humanorigins/ha/a_tree.html

Neandertal modern human

Gibraltar Child

Neandertal flute?

Neandertal Hybrid ? Modern Human (Cro-Magnon)

Erik Trinkaus (Washington University) thinks he has detected definite skeletal evidence of hybridizationPublished in PNAS, 2007

Trinkaus and team reported previously a possible hybrid on the Iberian peninsula in 1999 (Lagar-Velho 1)