Ardi

How did bipedalism evolve?
Dr.Raichlen and colleagues asserted that, from their studies on walking energetics and biomechanics among adult chimpanzees and humans, bipedalism reduced the energy cost of walking compared to our ape-like ancestors. Bipedal walking is 75% less costly than qaudrupedal knucklewalking.

Furthermore, Dr. Lovejoy, in the article Reexamining Human Origins in Light of Ardipithecus Ramidus, explains how bipedalism permits many advantages in the lifestyle and survival of early hominids. It allowed for the transport of food across long distances, permitted the use of tools, facilitated female sexual selection on mates in exchange for valuable food, and might have played a pivotal role in male parental investment.

What forces led to the evolution of larger brain size in our early primate ancestors?

Certainly, bipedalism played a crucial role. Free hands allowed for multitasking and thus improved neural connections and signaling in the brain. Moreover, ovulatory crypsis and other reproductive characters(proliferation of sex-related traits for mate selection etc.) have often been believed to intensify social behaviors and also allowed the rapid development of the "unusually enegry-thirsty brain." Conversely, the invention/acquisition of fire, or any other simple physical capacity does not solely explain the enlargment of the brain because they are believed to have proceeded or occurred in relation to such unique reproductive and behavioral strategies.

Genesis

In Conceit of Hindsight, Dawkins warns us against a pair of temptations. First, he briefly mentioned that we should not always seek for patterns when looking at evolutionary history, as if it aims to arrive at a certain destination or abide with certain rules. Albeit the fact that there are indeed some unifying theories, these concepts vary and we should still be cautious not to shrink it as such. Second, we should avoid seeing the past through the lens of our own existence. The laws of physics do not necessarily suggest that the universe was created so that we house in it; in fact Smolin theorized that our universe may have been a product of a random “mutation.” Also, all the different organisms throughout evolutionary history did not exist just to foreshadow us. We should avoid thinking that all species are “progressing” towards one main line of evolution, towards humans or any other modern species.

In Eve’s Tale, the Y-chromosome and mitochondrial DNA make tracing our ancestors easy. The non-recombining portion of the Y-chromosome always passes through the main line while the mitochondria exclusively passes along the female line, and thus these allow for studying a male or female line of ancestry plausible. However, these methods are limiting, because we could still trace ancestry lines without being confined to strict gender lines. Reliance on a single gene can be misleading. There are genes outside the Y-chromosome and the mitochondria that can still be passed from generation to generation.

Templeton was able to date back human migrations out of Africa through analyzing 13 haplotypes ( a long-lived recognizable chunk of DNA), coupled with fossil calibrations. He was able make inferences of our genetic history over the past 2M years and he found out that there were 3 major migrations out of the continent.