evolution of bipedalism and larger brain size

One factor that led to bipedalism in early hominids is the ability to carry objects. This would give an advantage because high quality food may have been difficult to find and so being able to collect and carry food would have led to greater survival. The reduction of canine size also played a role in the evolution of bipedalism because it allowed less aggressive males more access to females who were looking for more male parental investment in offspring. Males may have presented females with food as a gift in exchange for mating rights. This reduced a females search time for food and allowed her more time to devote to offspring. By providing the female food while she is caring for young, the male ensures the female will be able to reproduce again more quickly than if she were finding food for herself. This raises reproductive success of both the male and female which would have led to natural selection of bipedalism. The evolution of a larger brain size was favored by decreased canine size and an increased need for tool use. With the canines reduced for social and reproductive reasons the morphology of the cranium allowed more space for the brain. Fully terrestrial bipeds would have used tools to find/acquire food or may have used tools to fight for mates. Fighting for mating rights is done with use of canines in most modern apes and since the canines were already reduced in early Homo ancestors, fighting for mates would have to be done with sheer strength or tools.

Ancestors tale

In the first chapter of Ancestor's Tale, Dawkins presents two misconceptions to avoid. One is avoiding looking at the past from a future standpoint. The first chapter looks backwards from an evolutionary standpoint and Dawkins explains that evolution does not happen to reach a goal, it happens to better individual species and help them survive better. If, on looking back at evolutionary 'transitions', you have the notion that certain adaptations arose as a stepping stone to a certain goal then that is something you should avoid thinking. Another misconception Dawkins advises to avoid is looking for repeating patterns in history. While looking at the evolutionary tree you should not try to find recurring events or patterns since evolution does not happen on a schedule. Different lineages took different steps along history to result in the different species we have today and if patterns were common then all species would look similar.
Dawkins also tells how scientists determine when and how human ancestors migrated out of Africa. Dawkins explains the two main theories on the subject, 'out of Africa' and 'separate origins'. Scientists are trying to trace genes back to determine which theory is more correct. One way it is done is tracing haplotypes backwards through lineages. Some of these haplotypes include mitochondrial DNA and Y-chromosomes. Y-chromosome Adam tells us that all males have one common ancestor, Adam, and he is the first male (therefore has the first Y-chromosome). Since all males have a Y-chromosome all males must be descended from Adam. mtDNA Eve is the common ancestor to all females since mtDNA is passed on through the female line. Y-chromosome Adam and mtDNA Eve do not explain the whole story because there are many other genes to consider when considering earliest common ancestors.

Altruism is often explained by benefits of altruism going to a related individual. This is called kin selection and explains why seemingly altruistic behaviors are observed between individuals. One way altruism can evolve when benefits are not directed towards kin is being able to recognize faces. Knowing who you are interacting with may change the way you interact with that individual. This means you must also remember past interactions, which is another way altruism can evolve. If you know that the individual you are interacting with has helped you in the past, you will be more likely to help them. Vice versa, if you have helped an individual in the past, that individual will be more likely to help you in future interactions. This explains why vampire bats give blood meals to each other. They help each other survive, even though they are not related. If one individual A gave a blood meal to individual B, then when individual A asks individual B for a blood meal, individual B should oblige. This helps individuals survive and keeps them healthy, keeping group numbers up and helping everyone stay safe from predators (safety in numbers). Also, this means that offspring of one individual will have a better chance of finding a healthy mate, since the offspring of other individuals will most likely be mate choices. Altruism toward an unrelated individual may help offspring or other related individuals indirectly so it is best to be kind to others, even if they are not related to you.

The idea of kin selection is one that has been gone over many times by many authors. It explains why individuals help out family members for things such as raising young. But what explains the queen and her workers? Traditionally the queen is the only one that gets to lay eggs, the workers are unable to reproduce because they have not had any opportunities to fertilize their eggs. So why, if there is no chance for reproduction for the workers, do the workers diligently help the queen by raising the young and finding food for the hive. Dawkins brings up relatedness among social insects (excluding termites); according to him, workers are more closely related to the eggs the queen is producing than to the queen herself if that queen was the one who produced all the workers in the group. This means that it is benefiting the workers to care for the eggs since they share 3/4 of genes. In this way the queen wins because she is needed to keep producing more eggs. Dawkins explains social insects as a fully functioning body, the individuals of the group acting as parts of the body helping it function as a whole. If this is the case for most social insects then it is in every individuals best interest to work, to find food, and to protect other individuals so that each other individual will do the same. In this way the workers win because they each are taking care of themselves along with all the other workers who are participating and so in terms of individual survival the workers are more valuable to other workers than the queen.

Week 4

Darwin is probably most famous for his idea of natural selection and many people probably do not know Darwin also described sexual selection. Darwin describes natural selection as something that is always taking place to better the individual; maintaining changes that help the individual survive in it's environment. Darwin says that every change that is accumulated throughout an organisms life will probably effect the later life stages of the organism. These same changes will appear in the offspring at the same life stages they first appeared in the parent. Natural selection works to better the individual and eventually, should the change be beneficial to the organism, will better the population. Darwin describes sexual selection as maintaining changes that help males compete for females. In other words, sexual selection favors males with the characteristics that females look for in a mate. The males with these characteristics have better reproductive success and therefore offspring are more likely to have the desirable characteristics. Darwin credits sexual selection as the reason some species are sexually dimorphic (although he does not use that term).
Dawkins also describes both natural selection and sexual selection. Dawkins brings up the female point of view on sexual selection; how do I have offspring with the best genes? Answer: mate with the best male who presumably has the best genes. This puts pressure on the males to have the best genes to get the most mates. Dawkins explains natural selection in a more gene based way. Changes that are good for the individual will be maintained because they will help the gene machine survive and have better reproductive success. Natural selection, according to Dawkins, also includes changes that may not be helpful on their own but that are helpful to other genes and therefore helpful to the individual.

Dawkins introduces the idea of ESS (evolutionarily stable strategy) and offers an explanation for what this means. Dawkins says that organisms will choose a strategy that is unable to be improved by any other member of a population. He also explains that most members of the population must have this same strategy; with no alternate strategy able to better the chosen strategy it is stable and will lead to evolution. Along with the ESS is a population ratio that maintains the stability of the strategy. For Fisher, this population ratio is the ratio of males to females. Fisher argues that a stable sex ratio is 50:50 and that this is maintained and favored through natural selection. In terms of humans, cytoplasmic elements would be biased toward a 0:100 (males:females) ratio. Think of mitochondria and how mitochondrial DNA is inherited from the mother only. This type of inheritance would favor an all female sex ratio because males aren't needed to pass that type of information down generations. Autosomal chromosomes would be biased toward a 50:50 ratio because half of the information comes from the father and half comes from the mother. This implies that the population should have an equal sex ratio to produce the next generation and have all the same genetic variability (possibly more if mutation occurs) as the parental generation. Likewise, the sex chromosomes would favor a 50:50 ratio because there are only two options for a phenotype. This is not to say that because there are only two phenotypic options that each will be present in equal frequency, I mean to imply that natural selection will favor an equal population to keep the same (or more) variability. Like Dawkins' example of hawks and doves, there is a favored ratio and for sex chromosomes a 50:50 ratio will be favored.

Week 2

Dawkins and Mayhew have two different ideas on how the first replicating molecules developed into functioning organisms. Dawkins proposes the first replicator started out as a mutation and then more and more mutations created replicators that were different enough to be called different molecules. Although he does not say how, Dawkins says DNA molecules are "modern descendants" of the original replicators. Gene machines arose when replicators were competing for resources; the replicators that survived the competition "built survival machines for themselves to live in". These survival machines would have been the first organisms to arise. The organisms eventually developed into more complex organisms and led to what Dawkins calls the gene machine. On the other hand, Mayhew describes a more structured transition from replicator to organism. Mayhew postulates that the replicators came together to form chromosomes, the chromosomes being made up of more specialized DNA and RNA molecules. These organisms eventually give rise to multicellular organisms; later sexual reproduction is favored to asexual reproduction and finally plants and animals are formed. The most likely scenario is the one proposed by Mayhew. Mayhew gets into heterotrophic versus autotrophic origins and Dawkins sort of overlooks this debate in his description of how organisms arose. Mayhew recommends the idea of chemo-autotrophy as the first energy source and his reasons make sense. Mayhew says early cell membranes probably couldn't handle a heterotrophic lifestyle (devouring other organisms and excreting the waste), and that photosynthesis is a complicated process and had probably been developed after the first organisms existed. Dawkins' idea of molecule competition, and the idea that things happened strictly by accident is a little to chaotic for me. Mayhew describes a more structured set of events that are likely to occur. This is not to say that nothing happened by accident, I simply favor the more structured of the two arguments.